 




				  ECMA

	      EUROPEAN COMPUTER MANUFACTURERS ASSOCIATION
	      ___________________________________________







			    STANDARD ECMA-55


			     Minimal BASIC


































			      January 1978



























       +--------------------------------------------------------+
       |                                                        |
       |  Free copies of this ECMA standard are available from  |
       |  ECMA European Computer Manufacturers Association      |
       |  114 Rue du Rhône    -   1204 Geneva (Switzerland)     |
       |                                                        |
       +--------------------------------------------------------+







				  ECMA

	      EUROPEAN COMPUTER MANUFACTURERS ASSOCIATION
	      ___________________________________________







			    STANDARD ECMA-55


			     Minimal BASIC


































			      January 1978

BRIEF HISTORY
_____________

The first version of the language BASIC, acronym for _Beginner's
_All-purpose _Symbolic _Instruction _Code, was produced in 1964 at
the Dartmouth College in the USA. This version of the language
was oriented towards interactive use. Subsequently, a number of
implementations of the language were prepared, that differed in
part from the original one.

In 1974, the ECMA General Assembly recognized the need for a
standardized version of the language, and in September 1974 the
first meeting of the ECMA Committee TC 21, BASIC, took place.
In January 1974, a corresponding committee, X3J2, had been found-
ed in the USA.

Through a strict co-operation it was possible to maintain full
compatibility between the ANSI and ECMA draft standards. The ANSI
one was distributed for public comments in January 1976, and a
number of comments were presented by ECMA.

A final version of the ECMA Standard was prepared at the meeting
of June 1977 and adopted by the General Assembly of ECMA on
Dec. 14, 1977 as Standard ECMA-55.

			       _T_A_B_L_E_ _O_F_ _C_O_N_T_E_N_T_S
                                                              _P_a_g_e

1.  SCOPE                                                       1

2.  REFERENCES                                                  1

3.  DEFINITIONS                                                 1

    3.1  BASIC                                                  1
    3.2  Batch Mode                                             1
    3.3  End-of-Line                                            2
    3.4  Error                                                  2
    3.5  Exception                                              2
    3.6  Identifier                                             2
    3.7  Interactive Mode                                       2
    3.8  Keyword                                                2
    3.9  Line                                                   2
    3.10 Nesting                                                2
    3.11 Print Zone                                             3
    3.12 Rounding                                               3
    3.13 Significant Digits                                     3
    3.14 Truncation                                             3

4.  CHARACTERS AND STRINGS                                      3

5.  PROGRAMS                                                    5

6.  CONSTANTS                                                   6

7.  VARIABLES                                                   8

8.  EXPRESSIONS                                                 9

9.  IMPLEMENTATION SUPPLIED FUNCTIONS                          11

10. USER DEFINED FUNCTIONS                                     13

11. LET STATEMENT                                              14

12. CONTROL STATEMENTS                                         15

13. FOR AND NEXT STATEMENTS                                    17

14. PRINT STATEMENT                                            19

15. INPUT STATEMENT                                            21

16. READ AND RESTORE STATEMENTS                                23

17. DATA STATEMENT                                             24

18. ARRAY DECLARATIONS                                         25

19. REMARK STATEMENT                                           26

20. RANDOMIZE STATEMENT                                        26

TABLE 1 - BASIC Character Set                                  28

TABLE 2 - BASIC Code                                           29

APPENDIX 1  -  Organization of the Standard                    30

APPENDIX 2  -  Method of Syntax Specification                  32

APPENDIX 3  -  Conformance                                     34

APPENDIX 4  -  Implementation-defined Features                 35

				 - 1 -

1.  _S_C_O_P_E
    This Standard ECMA-55 is designed to promote the interchangeabi-
    lity of BASIC programs among a variety of automatic data process-
    ing systems. Subsequent Standards for the same purpose will de-
    scribe extensions and enhancements to this Standards. Programs
    conforming to this Standard, as opposed to extensions or enhance-
    ments of this Standard, will be said to be written in "Minimal
    BASIC".

    This Standard establishes:

    - the syntax of a program written in Minimal BASIC.

    - The formats of data and the precision and range of numeric re-
      presentations which are acceptable as input to an automatic
      data processing system being controlled by a program written
      in Minimal BASIC.

    - The semantic rules for interpreting the meaning of a program
      written in Minimal BASIC.

    - The errors and exceptional circumstances which shall be detect-
      ed and also the manner in which such errors and exceptional cir-
      cumstance shall be handled.

    Although the BASIC language was originally designed primarily for
    interactive use, this Standard describes a language that is not
    so restricted.

    The organization of the Standard is outlined in Appendix 1. The
    method of syntax specification used is explained in Appendix 2.

2.  _R_E_F_E_R_E_N_C_E_S

    ECMA-6  :  7-Bit Input/Output Coded Character Set, 4th Edition

    ECMA-53 :  Representation of Source Programs

3.  _D_E_F_I_N_I_T_I_O_N_S

    For the purposes of this Standard, the following terms have the
    meanings indicated.

 3.1  _B_A_S_I_C

      A term applied as a name to members of a special class of lan-
      guages which possess similar syntaxes and semantic meanings;
      acronym for Beginner's All-purpose Symbolic Instruction Code.

 3.2  _B_a_t_c_h_-_m_o_d_e

      The processing of programs in an environment where no provision
      is made for user interaction.

				 - 2 -

3.3  _E_n_d_-_o_f_-_l_i_n_e

     The character(s) or indicator which identifies the termination
     of a line. Lines of three kinds may be identified in Minimal
     BASIC: program lines, print lines and input reply lines.
     End-of-line may vary between the three cases and may also vary
     depending upon context. Thus, for example, an end of input
     line may vary on a given system depending on the terminal being
     used in interactive or batch mode.

     Typical examples of end-of-line are carriage-return, carriage-
     return line-feed, and end of record (such as end of card).

3.4  _E_r_r_o_r

     A flaw in the syntax of a program which causes the program to
     be incorrect.

3.5  _E_x_c_e_p_t_i_o_n

     A circumstance arising in the course of executing a program
     which results from faulty data or computations or from exceed-
     ing some resource constraint. Where indicated certain excep-
     tions (non-fatal exceptions) may be handled by the specified
     procedures; if no procedure is given (fatal exceptions) or if
     restrictions imposed by the hardware or operating environment
     make it impossible to follow the given procedure, then the ex-
     ception shall be handled by terminating the program.

3.6  _I_d_e_n_t_i_f_i_e_r

     A character string used to name a variable or a function.

3.7  _I_n_t_e_r_a_c_t_i_v_e_ _m_o_d_e

     The processing of programs in an environment which permits the
     user to respond directly to the actions of individual programs
     and to control the commencement and termination of those pro-
     grams.

3.8  _K_e_y_w_o_r_d

     A character string, usually with the spelling of a commonly
     used or mnemonic word, which provides a distinctive identifi-
     cation of a statement or a component of a statement of a pro-
     gramming language.

     The keywords in Minimal BASIC are: BASE, DATA, DEF, DIM, END,
     FOR, GO, GOSUB, GOTO, IF, INPUT, LET, NEXT, ON, OPTION, PRINT,
     RANDOMIZE, READ, REM, RESTORE, RETURN, STEP, STOP, SUB, THEN
     and TO.

3.9  _L_i_n_e

     A single transmission of characters which terminates with an
     end-of-line.

3.10 _N_e_s_t_i_n_g

     A set of statements is nested within another set of statements
     when:

				 - 3 -

      - the nested set is physically contiguous, and
      - the nesting set (divided by the nested set) is non-null.

 3.11 _P_r_i_n_t_ _z_o_n_e

      A contiguous set of character positions in a printed output
      line which may contain an evaluated print statement element.

 3.12 _R_o_u_n_d_i_n_g

      The process by which the representation of a value with lower
      precision is generated from a representation of higher preci-
      sion taking into account the value of that portion of the ori-
      ginal number which is to be omitted.

 3.13 _S_i_g_n_i_f_i_c_a_n_t_ _d_i_g_it_s

      The contiguous sequence of digits between the high-order non-
      zero digit and the low-order non-zero digit, without regard
      for the location of the radix point. Commonly, in a normalized
      floating point internal representation, only the significant
      digits of a representation are maintained in the significance.

      NOTE: The Standard requires that the ability of a conforming
            implementation to accept numeric representations be
            measured in terms of significant digits rather than the
            actual number of digits (that is including leading or
            trailing zeroes) in the representation.

 3.14 _T_r_u_n_c_a_t_i_o_n

      The process by which the representation of a value with lower
      precision is generated from a representation of higher preci-
      sion by merely deleting the unwanted low order digits of the
      original representation.

4.  _C_H_A_R_A_C_T_E_R_S_ _A_N_D_ _S_T_R_I_N_G_S

 4.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

      The character set for BASIC is contained in the ECMA 7-bit
      coded character set. Strings are sequences of characters and
      are used in BASIC programs as comments (see 19), as string con-
      stants (see 6), or as data (see 15).

 4.2  _S_y_n_t_a_x

      1. letter           = A/B/C/D/E/F/G/H/I/J/K/L/M/N/O/P/Q/R/S/T/
                            U/V/W/X/Y/Z
      2. digit            = 0/1/2/3/4/5/6/7/8/9
      3. string-character = quotation-mark / quoted-string-character
      4. quoted-string-   = exclamation-mark / number-sign / dollar-
         character          sign / percent-sign / ampersand /
                            apostrophe / left-parenthesis / right-
                            parenthesis / asterisk / comma / solidus /
                            colon / semi-colon / less-than-sign /
                            equals-sign / greater-than-sign /
                            question-mark / circumflex-accent /
                            underline / unquoted-string-character
      5. unquoted-string- = space / plain-string-character
         character

				 - 4 -

      6. plain-string-    = plus-sign / minus-sign / full-stop /
         character          digit / letter
      7. remark-string    = string-character*
      8. quoted-string    = quotation-mark quoted-string-character*
                            quotation-mark
      9. unquoted-string  = plain-string-character /
                            plain-string-character
                            unquoted-string-character*
                            plain-string-character

 4.3  _E_x_a_m_p_l_e_s

      ANY CHARACTERS AT ALL (?!*!!) CAN BE USED IN A "REMARK".
      "SPACES AND COMMAS CAN OCCUR IN QUOTED STRINGS."
      COMMAS CANNOT OCCUR IN UNQUOTED STRINGS.

 4.4  _S_e_m_a_n_t_i_c_s

      The letters shall be the set of upper-case Roman letters con-
      tained in the ECMA 7-bit coded character set in positions 4/1
      to 5/10.

      The digits shall be the set of arabic digits contained in the
      ECMA 7-bit coded character set in positions 3/0 to 3/9.

      The remaining string-characters shall correspond to the remain-
      ing graphic characters in position 2/0 to 2/15, 3/10 to 3/15
      and in positions 5/14, 5/15 of the ECMA 7-bit coded character
      set.

      The names of characters are specified in Table 1.

      The coding of characters is specified in Table 2; however, this
      coding applies only when programs and/or input/output data are
      exchanged by means of coded media.

 4.5  _E_x_c_e_p_t_i_o_n_s

      None.

 4.6  _R_e_m_a_r_k_s

      Other characters from the ECMA 7-bit coded character set (in-
      cluding control characters) may be accepted by an implementation
      and may have a meaning to some other processor (such as an editor)
      but have no prescribed meaning within this Standard. Programs
      containing characters other than the string-characters described
      above are not standard-conforming programs.

      The several kinds of characters and strings described by the
      syntax correspond to the various uses of strings in a BASIC
      program. Remark-strings may be used in remark-statements (see
      19). Quoted-strings may be used as string-constants (see 6).
      Unquoted-strings may be used in addition to quoted-strings as
      data elements (see 17) without being enclosed in quotation marks;
      unquoted-strings cannot contain leading or trailing spaces.

				 - 5 -
5.  _P_R_O_G_R_A_M_S
 5.1   _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n
       BASIC is a line-oriented language. A BASIC program is a sequence
       of lines, the last of which shall be an end-line and each of
       which contains a keyword. Each line shall contain a unique line-
       number which serves as a label for the statement contained in
       that line.

 5.2   _S_y_n_t_a_x
       1. program          = block* end-line
       2. block            = (line/for-block)*
       3. line             = line-number statement end-of-line
       4. line-number      = digit digit? digit? digit?
       5. end-of-line      = [implementation defined]
       6. end-line         = line-number end-statement end-of-line
       7. end-statement    = END
       8. statement        = data-statement / def-statement /
                             dimension -statement / gosub-statement /
                             goto-statement / if-then-statement /
                             input-statement / let-statement /
                             on-goto-statement / option-statement /
                             print-statement / randomize-statement /
                             read-statement / remark-statement /
                             restore-statement / return-statement /
                             stop statement

 5.3   _E_x_a_m_p_l_e_s

       999 END

 5.4   _S_e_m_a_n_t_i_c_s

       A BASIC program shall be composed of a sequence of lines order-
       ed by line-numbers, the last of which contains an end-statement.
       Program lines shall be executed in sequential order, starting
       with the first line, until

       - some other action is dictated by a control statement, or
       - an exception condition occurs, which results in a termination
         of the program, or
       - a stop-statement or end-statement is executed.

       Special conventions shall be observed regarding spaces. With
       the following exceptions, spaces may occur anywhere in a BASIC
       program without affecting the execution of that program and
       may be used to improve the appearance and readability of the
       program.

       Spaces shall not appear:

       - at the beginning of a line
       - within keywords
       - within numeric constants
       - within line numbers
       - within function or variable names
       - within two-character relation symbols

				 - 6 -

       All keywords in a program shall be preceded by at least one
       space and, if not at the end of a line, shall be followed by
       at least one space.

       Each line shall begin with a line-number. The values of the
       integers represented by the line-numbers shall be positive
       nonzero; leading zeroes shall have no effect. Statements shall
       occur in ascending line-number order.

       The manner in which the end of a statement line is detected is
       determined by the implementation; e.g. the end-of-line may be
       a carriage-return character, a carriage-return character follow-
       ed by a line-feed character, or the end of a physical record.

       Lines in a standard-conforming program may contain up to 72
       characters; the end-of-line indicator is not included within
       this 72 character limit.

       The end-statement serves both to mark the physical end of the
       main body of a program and to terminate the execution of the
       program when encountered.

  5.5  _E_x_c_e_p_t_i_o_n_s

       None.

  5.6  _R_e_m_a_r_k_s

       Local editing facilities may allow for the entry of statement
       lines in any order and also allow for duplicate line-numbers
       and lines containing only a line-number. Such editing facili-
       ties usually sort the program into the proper order and in the
       case of duplicate line-numbers, the last line entered with
       that line-number is retained. In many implementations, a line
       containing only a line-number (without trailing spaces) is
       usually deleted from the program.

 6.  _C_O_N_S_T_A_N_T_S

  6.1  _G_e_n_e_r_a_l_ _d_e_s_c_r_i_p_t_i_o_n

       Constants can denote both scalar numeric values and string
       values.

       A numeric-constant is a decimal representation in positional
       notation of a number. There are four general syntactic forms
       of (optionally signed) numeric constants:

       - implicit point representation              sd...d
       - explicit point unscaled representation     sd..drd..d
       - explicit point scaled representation       sd..drd..dEsd..d
       - implicit point scaled representation       sd..dEsd..d

       where:

       d is a decimal digit,
       r is a full-stop
       s is an optional sign, and
       E is the explicit character E.

				 - 7 -
       A string-constant is a character string enclosed in quotation
       marks (see 4).

  6.2  _S_y_n_t_a_x

       1. numeric-constant  = sign? numeric-rep
       2. sign              = plus-sign / minus-sign
       3. numeric-rep       = significand exrad?
       4. significand       = integer full-stop? / integer? fraction
       5. integer           = digit digit*
       6. fraction          = full-stop digit digit*
       7. exrad             = E sign? integer
       8. string-constant   = quoted-string

  6.3  _E_x_a_m_p_l_e_s

       1        500          -21.         .255        1E10
       5E-1     .4E+1
       "XYZ"              "X - 3B2"            "1E10"

  6.4  _S_e_m_a_n_t_i_c_s

       The value of a numeric-constant is the number represented by
       that constant. "E" stands for "times ten to the power"; if no
       sign follows the symbol "E", then a plus sign is understood.
       Spaces shall not occur in numeric-constants.

       A program may contain numeric representations which have an
       arbitrary number of digits, though implementations may round
       the values of such representations to an implementation-defined
       precision of not less than six significant decimal digits. Numeric
       constants can also have an arbitrary number of digits in the ex-
       rad, though nonzero constants whose magnitude is outside an im-
       plementation-defined range will be treated as exceptions. The
       implementation-defined range shall be at least 1E-38 to 1E+38.
       Constants whose magnitudes are less than machine infinitesimal
       shall be replaced by zero, while constants whose magnitudes are
       larger than machine infinity shall be diagnosed as causing an
       overflow.

       A string-constant has as its value the string of all characters
       between the quotation marks; spaces shall not be ignored. The
       length of a string-constant, i.e. the number of characters con-
       tained between the quotation-marks, is limited only by the length
       of a line.

  6.5  _E_x_c_e_p_t_i_o_n_s

       The evaluation of a numeric constant causes an overflow (non-
       fatal, the recommended recovery procedure is to supply machine
       infinity with the appropriate sign and continue).

  6.6  _R_e_m_a_r_k_s

       Since this Standard does not require that strings with more
       than  18 characters be assignable to string variables (see 7),
       conforming programs can use string constants with more than
       18 characters only as elements in a print-list.

				 - 8 -
       It is recommended that implementations report constants whose
       magnitudes are less than machine infinitesimal as underflows
       and continue.

 7.  _V_A_R_I_A_B_L_E_S

  7.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       Variables in BASIC are associated with either numeric or
       string values and, in the case of numeric variables, may be
       either simple variables or references to elements of one or
       two dimensional arrays; such references are called subscript-
       ed variables.

       Simple numeric variables shall be named by a letter followed
       by an optional digit.

       Subscripted numeric variables shall be named by a letter fol-
       lowed by one or two numeric expressions enclosed within pa-
       rentheses.

       String variables shall be named by a letter followed by a
       dollar sign.

       Explicit declarations of variable types are not required; a
       dollar-sign serves to distinguish string from numeric variab-
       les, and the presence of a subscript distinguishes a sub-
       scripted variable from a simple one.

  7.2  _S_y_n_t_a_x

       1. variable               = numeric-variable / string-variable
       2. numeric-variable       = simple-numeric-variable /
                                   numeric-array-element
       3. simple-numeric-        = letter digit?
          variable
       4. numeric-array-element  = numeric-array-name subscript
       5. numeric-array-name     = letter
       6. subscript              = left-parenthesis numeric-expression
                                   (comma numeric-expression)? right-
                                   parenthesis
       7. string-variable        = letter dollar-sign

  7.3  _E_x_a_m_p_l_e_s

       X         A5        V(3)        W(X,X+Y/2)
       S$        C$

  7.4  _S_e_m_a_n_t_i_c_s

       At any instant in the execution of a program, a numeric-
       variable is associated with a single numeric value and a
       string-variable is associated with a single string value.
       The value associated with a variable may be changed by the
       execution of statements in the program.

				 - 9 -

       The length of the character string associated with a string-
       variable can vary during the execution of a program from a
       length of zero characters (signifying the null or empty string)
       to 18 characters.

       Simple-numeric-variables and string-variables are declared im-
       plicitly through their appearance in a program.

       A subscripted variable refers to the element in the one or two
       dimensional array selected by the value(s) of the subscript(s).
       The value of each subscript is rounded to the nearest integer.
       Unless explicitly declared in a dimension statement, subscript-
       ed variables are implicitly declared by their first appearance
       in a program. In this case the range of each subscript is from
       zero to ten inclusive, unless the presence of an option-state-
       ment indicates that the range is from one to ten inclusive. Sub-
       script expressions shall have values within the appropriate range
       (see 18).

       The same letter shall not be the name of both a simple variable
       and an array, nor the name of both a one-dimensional and a two-
       dimensional array.

       There is no relationship between a numeric-variable and a string-
       variable whose names agree except for the dollar-sign.

       At the initiation of execution the values associated with all
       variables shall be implementation-defined.

  7.5  _E_x_c_e_p_t_i_o_n_s

       A subscript is not in the range of the explicit or implicit
       dimensioning bounds (fatal).

  7.6  _R_e_m_a_r_k_s

       Since initialization of variables is not specified, and hence
       may vary from implementation to implementation, programs that
       are intended to be transportable should explicitly assign a
       value to each variable before any expression involving that
       variable is evaluated.

       There are many commonly used alternatives for associating im-
       plementation-defined initial values with variables; it is re-
       commended that all variables are recognizably undefined in the
       sense that an exception will result from any attempt to access
       the value of any variable before that variable is explicitly
       assigned a value.

 8.  _E_X_P_R_E_S_S_I_O_N_S

  8.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       Expressions shall be either numeric-expressions or string-
       expressions.

       Numeric-expressions may be constructed from variables, constants,
       and function references using the operations of addition, sub-
       traction, multiplication, division and involution.

				 - 10 -

       String-expressions are composed of either a string-variable or
       a string-constant.

  8.2  _S_y_n_t_a_x

       1. expression         = numeric-expression / string-expression
       2. numeric-expression = sign? term (sign term)*
       3. term               = factor (multiplier factor)*
       4. factor             = primary (circumflex-accent primary)*
       5. multiplier         = asterisk / solidus
       6. primary            = numeric-variable / numeric-rep / numeric-
                               function-ref / left-parenthesis numeric-
                               expression
                               right-parenthesis
       7. numeric-function-  = numeric-function-name
          ref                  argument-list?
       8. numeric-function-  = numeric-defined-function /
          name                 numeric-supplied-function
       9. argument-list      = left-parenthesis argument
                               right-parenthesis
      10. argument           = string-expression
      11. string-expression  = string-variable / string-constant
      
  8.3  _E_x_a_m_p_l_e_s

       3*X - Y^2        A(1)+A(2)+A(3)         2^(-X)
       -X/Y             SQR(X^2+Y^2)

  8.4  _S_e_m_a_n_t_i_c_s

       The formation and evaluation of numeric-expressions follows the
       normal algebraic rules. The symbols circumflex-accent, asterisk,
       solidus, plus-sign and minus-sign represent the operations of
       involution, multiplication, division, addition and subtraction,
       respectively. Unless parentheses dictate otherwise, involutions
       are performed first, then multiplications and divisions, and
       finally additions and subtractions. In the absence of parenthe-
       ses, operations of the same precedence are associated to the
       left.

       A-B-C is interpreted as (A-B)-C, A^B^C as (A^B)^C, A/B/C as
       (A/B)/C and -A^B as -(A^B).

       If an underflow occurs in the evaluation of a numeric expression
       then the value generated by the operation which resulted in the
       underflow shall be replaced by zero.

       0^0 is defined to be 1, as in ordinary mathematical usage.

       When the order of evaluation of an expression is not constrained
       by the use of parentheses, and if the mathematical use of opera-
       tors is associative, commutative, or both, then full use of these
       properties may be made in order to revise the order of evalua-
       tion of the expression.

       In a function reference, the number of arguments supplied shall
       be equal to the number of parameters required by the definition
       of the function.

				 - 11 -

       A function reference is a notation for the invocation of a pre-
       defined algorithm, into which the argument value, if any, is
       substituted for the parameter (see 9 and 10) which is used in
       the function definition. All functions referenced in an express-
       ion shall either be implementation-supplied or be defined in a
       def-statement. The result of the evaluation of the function,
       achieved by the execution of the defining algorithm, is a scalar
       numeric value which replaces the function reference in the ex-
       pression.

  8.5  _E_x_c_e_p_t_i_o_n_s

       - Evaluation of an expression results in division by zero
         (nonfatal, the recommended recovery procedure is to supply
         machine infinity with the sign of the numerator and continue)

       - Evaluation of an expression results in an overflow (nonfatal,
         the recommended recovery procedure is to supply machine in-
         finity with the algebraically correct sign and continue).

       - Evaluation of the operation of involution results in a nega-
         tive number being raised to a non-integral power (fatal).

       - Evaluation of the operation of involution results in a zero be-
         ing raised to a negative value (nonfatal, the recommended re-
         covery procedure is to supply positive machine infinity and
         continue).

  8.6  _R_e_m_a_r_k_s

       The accuracy with which the evaluation of an expression takes
       place will vary from implementation to implementation. While no
       minimum accuracy is specified for the evaluation of numeric-
       expressions, it is recommended that implementations maintain at
       least six significant decimal digits of precision.

       The method of evaluation of the operation of involution may
       depend upon whether or not the exponent is an integer. If it
       is, then the indicated number of multiplications may be per-
       formed; if it is not, then the expression may be evaluated
       using the LOG and EXP functions (see 9).

       It is recommended that implementations report underflow as an
       exception and continue.

 9.  _I_M_P_L_E_M_E_N_A_T_A_T_I_ON_ _S_U_P_P_L_I_E_D_ _F_U_N_C_T_I_O_N_S

  9.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       Predefined algorithms are supplied by the implementation for
       the evaluation of commonly used numeric functions.

  9.2  _S_y_n_t_a_x

       1. numeric-supplied-function = ABS / ATN / COS / EXP / INT /
                                      LOG / RND / SGN / SIN / SQR / TAN
  9.3  _E_x_a_m_p_l_e_s

       None.

				 - 12 -
  9.4  _S_e_m_a_n_t_i_c_s

       The values of the implementation-supplied functions, as well as
       the number of arguments required for each function, are described
       below. In all cases, X stands for a numeric expression.

       _F_u_n_c_t_i_o_n          _F_u_n_c_t_i_o_n_ _v_a_l_u_e

       ABS(X)            The absolute value of X.

       ATN(X)            The arctangent of X in radians, i.e. the angle
                         whose tangent is X. The range of the function
                         is
                               -(pi/2) < ATN(X) < (pi/2)
                         where pi is the ratio of the circumference of
                         a circle to its diameter.

       COS(X)            The cosine of X, where X is in radians.

       EXP(X)            The exponential of X, i.e. the value of the
                         base of natural logarithms (e = 2,71828...)
                         raised to the power X; if EXP(X) is less than
                         machine infinitesimal, then its value shall
                         be replaced by zero.

       INT(X)            The largest integer not greater than X; e.g.
                         INT(1.3) = 1 and INT(-1.3) = -2.

       LOG(X)            The natural logarithm of X; X must be greater
                         than zero.

       RND               The next pseudo-random  number in an implemen-
                         tation-supplied sequence of pseudo-random num-
                         bers uniformly distributed in the range 0 <=
                         RND < 1 (see also 20).

       SGN(X)            The sign of X: -1 if X < 0, 0 if X = 0 and
                         +1 if X > 0.

       SIN(X)            The sine of X, where X is in radians.

       SQR(X)            The nonnegative square root of X; X must be
                         nonnegative.

       TAN(X)            The tangent of X, where X  is in radians.

  9.5  _E_x_c_e_p_t_i_o_n_s

       - The value of the argument of the LOG function is zero or ne-
         gative (fatal).

       - The value of the argument of the SQR function is negative
         (fatal).

       - The magnitude of the value of the exponential or tangent
         function is larger than machine infinity (nonfatal, the re-
         commended recovery procedure is to supply machine infinity
         with the appropriate sign and continue).

				 - 13 -

  9.6  _R_e_m_a_r_k_s

       The RND function in the absence of a randomize-statement (see
       20) will generate the same sequence of pseudo-random numbers
       each time a program is run. This convention is chosen so that
       programs employing pseudo-random numbers can be executed se-
       veral times with the same result.

       It is recommended that, if the value of the exponential function
       is less than machine infinitesimal, implementations report this
       as an underflow and continue.


10.  _U_S_E_R_ _D_E_F_I_N_E_D_ _F_U_N_C_T_I_O_N_S

 10.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       In addition to the implementation supplied functions provided
       for the convenience of the programmer (see 9), BASIC allows
       the programmer to define new functions within a program.

       The general form of statements for defining functions is

                    DEF FNx = expression
       or           DEF FNx (parameter) = expression

       where x is a single letter and a parameter is a simple numeric-
       variable.

 10.2  _S_y_n_t_a_x

       1. def-statement      = DEF numeric-defined-function
                               parameter-list? equals-sign
                               numeric-expression
       2. numeric-defined-
          function           = FN letter
       3. parameter-list     = left-parenthesis parameter
                               right-parenthesis
       4. parameter          = simple-numeric-variable

 10.3  _E_x_a_m_p_l_e_s

       DEF FNF(X) = X^4 - 1    DEF FNP = 3.14159
       DEF FNA(X) = A*X + B

 10.4  _S_e_m_a_n_t_i_c_s

       A function definition specifies the means of evaluation the
       function in terms of the value of an expression involving the
       parameter appearing in the parameter-list and possibly other
       variables or constants. When the function is referenced, i.e.
       when an expression involving the function is evaluated, then
       the expression in the argument list for the function reference,
       if any, is evaluated and its value is assigned to the parameter
       in the parameter-list for the function definition (the number
       of arguments shall correspond exactly to the number of para-
       meters). The expression in the function definition is then eva-
       luated, and this value is assigned as the value of the function.

				 - 14 -

       The parameter appearing in the parameter-list of a function
       definition is local to that definition, i.e. it is distinct
       from any variable with the same name outside of the function
       definition. Variables which do not appear in the parameter-
       list are the variables of the same name outside the function
       definition.

       A function definition shall occur in a lower numbered line
       than that of the first reference to the function. The expres-
       sion in a def-statement is not evaluated unless the defined
       function is referenced.

       If the execution of a program reaches a line containing a
       def-statement, then it shall proceed to the next line with no
       other effect.

       A function definition may refer to other defined functions,
       but not to the function being defined. A function shall be de-
       fined at most once in a program.

 10.5  _E_x_c_e_p_t_i_o_n_s

       None.

11.  _L_E_T_ _S_T_A_T_E_M_E_N_T

 11.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       A let-statement provides for the assignment of the value of
       an expression to a variable. The general syntactic form of
       the let-statement shall be

                     LET variable = expression

 11.2  _S_y_n_t_a_x

       1. let-statement           = numeric-let-statement /
                                    string-let-statement
       2. numeric-let-statement   = LET numeric-variable equals-sign
                                    numeric-expression
       3. string-let-statement    = LET string-variable equals-sign
                                    string-expression

 11.3  _E_x_a_m_p_l_e_s

       LET P = 3.14159
       LET A(X,3) = SIN(X)*Y + 1

       LET A$ = "ABC"
       LET A$ = B$

 11.4  _S_e_m_a_n_t_i_c_s

       The expression is evaluated (see 8) and its value is assigned
       to the variable to the left of the equals sign.

 11.5  _E_x_c_e_p_t_i_o_n_s

       A string datum contains too many characters (fatal).

				 - 15 -

12.  _C_O_N_T_R_O_L_ _S_T_A_T_E_M_E_N_T_S

 12.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       Control statements allow for the interruption of the normal
       sequence of execution of statements by causing execution to
       continue at a specified line, rather than at the one with the
       next higher line number.

       The goto-statement

                     GO TO line-number

       allows for an unconditional transfer.

       The if-then-statement

                     IF exp1 rel exp2 THEN line-number

       where "exp1" and "exp2" are expressions and "rel" is a relation-
       al operator, allows for a conditional transfer.

       The gosub and return statements

                     GO SUB line-number
                     RETURN

       allow for subroutine calls.

       The on-goto-statement

                     ON expression GO TO line-number, ..., line-number

       allows control to be transferred to a selected line.

       The stop-statement

                     STOP

       allows for program termination.

 12.2  _S_y_n_t_a_x

       1. goto-statement           = GO space* TO line-number
       2. if-then-statement        = IF relational-expression THEN
                                     line-number
       3. relational-expression    = numeric-expression relation
                                     numeric-expression / string-
                                     expression equality-relation
                                     string-expression
       4. relation                 = equality-relation / less-than-
                                     sign / greater-than-sign / not-
                                     less / not-greater
       5. equality-relation        = equals-sign / not-equals
       6. not-less                 = greater-than-sign equals-sign
       7. not-greater              = less-than-sign equals-sign
       8. not-equals               = less-than-sign  greater-than-sign
       9. gosub-statement          = GO space* SUB line-number
      10. return-statement         = RETURN
      11. on-goto-statement        = ON numeric-expression GO space*
                                     TO line-number (comma line-number)*

				 - 16 -

      12. stop-statement           = STOP

 12.3  _E_x_a_m_p_l_e_s

       GO TO 999                   IF X > Y+83 then 200
       IF A$ <> B$ THEN 550        ON L+1 GO TO 300,400,500

 12.4  _S_e_m_a_n_t_i_c_s

       A goto-statement indicates that execution of the program is to
       be continued at the specified line-number.

       If the value of the relational-expression in an if-then-state-
       ment is true, then execution of the program shall continue from
       the specified line-number; if the value of the relational-ex-
       pression is false, then execution shall be continued in sequence,
       i.e. with the statement on the line following that containing
       the if-then-statement.

       The relation "less than or equal to" shall be denoted by <=.
       Similarly, "greater than or equal to" shall be denoted by >=,
       while "not equal to" shall be denoted by <>.

       The relation of equality holds between two strings if and only
       if the two strings have the same length and contain identical
       sequences of characters.

       The execution of the gosub-statement and the return-statement
       can be described in terms of a stack of line-numbers (but may
       be implemented in some other fashion). Prior to execution of
       the first gosub-statement by the program, this stack is empty.
       Each time a gosub-statement is executed, the line-number of
       the gosub-statement is placed on top of the stack and execution
       of the program is continued at the line specified in the gosub-
       statement. Each time a return-statement is executed, the line-
       number on top of the stack is removed from the stack and exe-
       cution of the program is continued at the line following the
       one with that line-number.

       It is not necessary that equal numbers of gosub-statements and
       return-statements be executed before termination of the program.

       The expression in an on-goto-statement shall be evaluated and
       rounded to obtain an integer, whose value is then used to select
       a line-number from the list following the GOTO (the line-numbers
       in the list are indexed from left to right, starting with 1).
       Execution of the program shall continue at the statement with
       the selected line-number.

       All line-numbers in control-statements shall refer to lines in
       the program.

       The stop-statement causes termination of the program.

 12.5  _E_x_c_e_p_t_i_o_n_s

       - An attempt is made to execute a return-statement without
         having executed a corresponding gosub-statement (fatal).

				 - 17 -

       - The integer obtained as the value of an expression in an
         on-goto-statement is less than one or greater than the
         number of line-numbers in the list (fatal).

13.  _F_O_R_ _A_N_D_ _N_E_X_T_ _S_T_A_T_E_M_E_N_T_S

 13.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       The for-statement and next-statement provide for the contruct-
       ion of loops. The general syntactic form of the for-statement
       and next-statement is

                    FOR v = initial-value TO limit STEP increment
                    NEXT v

       where "v" is a simple numeric variable and the "initial-value",
       "limit" and "increment" are numeric expressions; the clause
       "STEP increment" is optional.

 13.2  _S_y_n_t_a_x

       1. for-block                = for-line for-body
       2. for-body                 = block next-line
       3. for-line                 = line-number for-statement end-of-
                                     line
       4. next-line                = line-number next-statement end-
                                     of-line
       5. for-statement            = FOR control-variable equals-sign
                                     initial-value TO limit (STEP
                                     increment)?
       6. control-variable         = simple-numeric-variable
       7. initial-value            = numeric-expression
       8. limit                    = numeric-expression
       9. increment                = numeric-expression
      10. next-statement           = NEXT control-variable

 13.3  _E_x_a_m_p_l_e_s

       FOR I = 1 TO 10             FOR I = A TO B STEP -1
       NEXT I                      NEXT I

 13.4  _S_e_m_a_n_t_i_c_s

       The for-statement and the next-statement are defined in con-
       junction with each other. The physical sequence of statements
       beginning with a for-statement and continuing up to and in-
       cluding the first next-statement with the same control variable
       is termed a "for-block". For-blocks can be physically nested,
       i.e. one can contain another, but they shall not be interleaved,
       i.e. a for-block which contains a for-statement or a next-
       statement shall contain the entire for-block begun or ended by
       that statement.

       Furthermore, physically nested for-blocks shall not use the
       same control variable.

				 - 18 -

       In the absence of a STEP clause in a for-statement, the incre-
       ment is assumed to be +1.

       The action of the for-statement and the next-statement is de-
       fined in terms of other statements, as follows:

              FOR v = initial-value TO limit STEP increment
              (block)
              NEXT v

       is equivalent to:

              LET own1 = limit
              LET own2 = increment
              LET v = initial-value
       line1  IF (v-own1) * SGN (own2) > 0 THEN line2
              (block)
              LET v = v + own2
              GOTO line1
       line2  REM continued in sequence

       Here v is any simple-numeric-variable, own1 and own2 are va-
       riables associated with the particular for-block and not ac-
       cessible to the programmer, and line1 and line2 are line-numbers
       associated with the particular for-block and not accessible to
       the programmer. The variables own1 and own2 are distinct from
       similar variables associated with other for-blocks. A program
       shall not transfer control into a for-body by any statement
       other than a return statement (see 12).

 13.5  _E_x_c_e_p_t_i_o_n_s

       None.

 13.6  _R_e_m_a_r_k_s

       Where arithmetic is approximate (as with decimal fractions in a
       binary machine), the loop will be executed within the limits of
       machine arithmetic. No presumptions about approximate achieve-
       ment of the end test are made. It is noted that in most ordinary
       situations where machine arithmetic is truncated (rather than
       rounded), such constructions as

               FOR X = 0 TO 1 STEP 0.1

       will work as the user expects, even though 0.1 is not represent-
       able exactly in a binary machine. If this is indeed the case,
       then the construction

               FOR X = 1 TO 0 STEP -0.1

       will probably not work as expected.

       As specified above, the value of the control-variable upon
       exit from a for-block via its next-statement is the first va-
       lue not used; if exit is via a control-statement, the control-
       variable retains the value it has when the control-statement
       is executed.

       The variables "own1" and "own2" associated with a for-block are
       assigned values only upon entry to the for-block through its
       for-statement.

				 - 19 -

14.  _P_R_I_N_T_ _S_T_A_T_E_M_E_N_T

 14.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       The print-statement is designed for generation of tabular out-
       put in a consistent format.

       The general syntactic form of the print-statement is

                PRINT item p item p ... p item

       where each item is an expression, a tab-call, or null, and
       each punctuation mark p is either a comma or a semi-colon.

 14.2  _S_y_n_t_a_x

       1. print-statement       = PRINT print-list?
       2. print-list            = (print-item? print-separator)*
                                  print_item?
       3. print-item            = expression / tab-call
       4. tab-call              = TAB left-parenthesis numeric-expres-
                                  sion right-parenthesis
       5. print-separator       = comma / semicolon

 14.3  _E_x_a_m_p_l_e_s

       PRINT X                           PRINT "X EQUALS", 10
       PRINT X; (X+Z)/2                  PRINT X, Y
       PRINT                             PRINT ,,,X
       PRINT TAB(10); A$; "IS DONE."

 14.4  _S_e_m_a_n_t_i_c_s

       The execution of a print-statement generates a string of char-
       acters for transmission to an external device. This string of
       characters is determined by the successive evaluation of each
       print-item and print-separator in the print-list.

       Numeric-expressions shall be evaluated to produce a string of
       characters consisting of a leading space if the number is po-
       sitive or a leading minus-sign if the number is negative fol-
       lowed by the decimal representation of the absolute value of
       the number and a trailing space. The possible formats for the
       decimal representation of a number are the same as those des-
       cribed for numeric-constants in 6 and are used as follows.

       Each implementation shall define two quantities, a significance-
       width d to control the number of significant decimal digits
       printed in numeric representations, and an exrad-width e to con-
       trol the number of digits printed in the exrad component of a
       numeric representation. The value of d shall be at least six
       and the value of e shall be at least two.

       Each number that can be represented exactly as an integer with
       d or fewer decimal digits is output using the implicit point
       unscaled representation.

       All other numbers shall be output using either explicit point
       unscaled notation or explicit point scaled notation. Numbers
       which can be represented with d or fewer digits in the unscaled
       format no less accurately than they can be represented in the
       scaled format shall be output using the unscaled format. For
       example, if d = 6, then 10^(-6) is output as .000001 and

				 - 20 -

       10^(-7) is output as 1.E-7.

       Numbers represented in the explicit point unscaled notation shall
       be output with up to d significant decimal digits and a full-
       stop; trailing zeroes in the fractional part may be omitted.
       A number with magnitude less than 1 shall be represented with
       no digits to the left of the full-stop. This form requires up
       to d+3 characters counting the sign, the full-stop and the
       trailing space.

       Numbers represented in the explicit point scaled notation shall
       be output in the format

               significand E sign integer

       where the value x of the significand is in the range 1 <= x < 10
       and is to be represented with exactly d digits of precision, and
       where the exrad component has one to e digits. Trailing zeroes
       may be omitted in the fractional part of the significand and
       leading zeroes may be omitted from the exrad. This form re-
       quires up to d+e+5 characters counting the two signs, the full-
       stop, the "E" and a trailing space.

       String-expressions shall be evaluated to generate a string of
       characters.

       The evaluation of the semicolon separator shall generate the
       null string, i.e. a string of zero length.

       The evaluation of a tab-call or a comma separator depends upon
       the string of characters already generated by the current or
       previous print-statements. The "current line" is the (possibly
       empty) string of characters generated since the last end-of-
       line was generated. The "margin" is the number of characters,
       excluding the end-of-line character, that can be output on one
       line and is defined by the implementation. The "columnar posi-
       tion" of the current line is the print position that will be
       occupied by the next character output to that line; print posi-
       tions are numbered consecutively from the left, starting with
       position one.

       Each print-line is divided into a fixed number of print zones,
       where the number of zones and the length of each zone is im-
       plementation defined. All print zones, except possibly the last
       one on a line, shall have the same length. This length shall
       be at least d+e+6 characters in order to accommodate the print-
       ing of numbers in explicit point scaled notation as des-
       cribed above and to allow the comma separator to move the print-
       ing mechanism to the next zone as described below.

       The purpose of the tab-call is to set the columnar position of
       the current line to the specified value prior to printing the
       next print-item. More precisely, the argument of the tab-call
       is evaluated and rounded to the nearing integer n. IF n is less
       than one, an exception occurs. If n is greater than the margin
       m, then n is reduced by an integral multiple of m so that it
       is in the range 1 <= n <= m; i.e. n is set equal to

				 - 21 -

                 n - m * INT ((n-1)/m).

       If the columnar position of the current line is less than or
       equal to n, then spaces are generated, if necessary, to set the
       columnar position to n; if the columnar position of the current
       line is greater than n, then an end-of-line is generated follow-
       ed by enough spaces to set the columnar position of the new cur-
       rent line to n.

       The evaluation of the comma-separator generates one or more
       spaces to set the columnar position to the beginning of the
       next print zone, unless the current print zone is the last on
       the line, in which case an end-of-line is generated.

       If the print list does not end in a print-separator, then an
       end-of-line is generated and added to the characters generated
       by the evaluation of the print-list.

       If the evaluation of any print-item in a print-list would cause
       the length of a nonempty line to exceed the margin, then an
       end-of-line is generated prior to the characters generated by
       that print-item. Subsequently, if the evaluation of a print-
       item generates a string whose length is greater than the mar-
       gin, then end-of-lines are inserted after every m characters
       in the string, where m is the margin value.

 14.5  _E_x_c_e_p_t_i_o_n_s

       The evaluation of a tab-call argument generates a value less
       then one (nonfatal; the recommended recovery procedure is to
       supply one and continue).

 14.6  _R_e_m_a_r_k_s

       The comma-separator allows the programmer to tabulate the print-
       ing mechanism to fixed tab settings at the end of each print
       zone.

       A completely empty print-list will generate an end-of-line,
       thereby completing the current line of output. If this line
       contained no characters, then a blank line results.

       A print line on a typical terminal might be divided into five
       print zones of fifteen print positions each.

15.  _I_N_P_U_T_ _S_T_A_T_E_M_E_N_T

 15.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       Input-statements provide for user interaction with a running
       program by allowing variables to be assigned values that are
       supplied by a user. The input-statement enables the entry of
       mixed string and numeric data, with data items being separat-
       ed by commas. The general syntactic form of the input-state-
       ment is

                     INPUT variable, ..., variable

				 - 22 -

 15.2  _S_y_n_t_a_x

       1. input-statement       = INPUT variable-list
       2. variable-list         = variable (comma variable)*
       3. input-prompt          = [implementation defined]
       4. input-reply           = input-list end-of-line
       5. input-list            = padded-datum (comma padded-datum)*
       6. padded-datum          = space* datum space*
       7. datum                 = quoted-string / unquoted-string

 15.3  _E_x_a_m_p_l_e_s

       INPUT X          INPUT X, A$, Y(2)      INPUT A, B, C
       3.14159          2,SMITH,-3             25,0,-15

 15.4  _S_e_m_a_n_t_i_c_s

       An input-statement causes the variables in the variable-list
       to be assigned, in order, values from the input-reply. In the
       interactive mode, the user of the program is informed of the
       need to supply data by the output of an input-prompt. In batch
       mode, the input-reply is requested from the external source
       by an implementation-defined means. Execution of the program
       is suspended until a valid input-reply has been supplied.

       The type of each datum in the input-reply shall correspond to
       the type of the variable to which it is to be assigned; i.e.,
       numeric-constants shall be supplied as input for numeric-
       variables, and either quoted-strings or unquoted-strings shall
       be supplied as input for string-variables. If the response to
       input for a string-variable is an unquoted-string, leading
       and trailing spaces shall be ignored (see 4).

       If the evaluation of a numeric datum causes an underflow, then
       its value shall be replaced by zero.

       Subscript expressions in the variable-list are evaluated after
       value have been assigned to the variables preceding them
       (i.e. to the left of them) in the variable-list.

       No assignment of values in the input-reply shall take place un-
       til the input-reply has been validated with respect to the type
       of each datum, the number of input items, and the allowable
       range for each datum.

 15.5  _E_x_c_e_p_t_i_o_n_s

       - The type of datum does not match the type of the variable to
         which it is to be assigned (nonfatal, the recommended recov-
         ery procedure is to request that the input-reply be re-sup-
         plied).

       - There is insufficient data in the input-list (nonfatal, the
         recommended recovery procedure is to request that the input-
         reply be resupplied).

       - There is too much data in the input-list (nonfatal, the re-
         commended recovery procedure is to request that the input-
         reply be resupplied).

				 - 23 -

       - The evaluation of a numeric datum causes an overflow (non-
         fatal, the recommended recovery procedure is to request that
         the input-reply be resupplied).

       - A string datum contains too many characters (nonfatal, the
         recommended recovery procedure is to request that the input-
         reply be resupplied).

 15.6  _R_e_m_a_r_k_s

       This Standard does not require an implementation to perform
       any editing of the input-reply, though such editing may be per-
       formed by the operating environment.

       It is recommended that the input-prompt consists of a question-
       mark followed by a single space.

       This Standard does not require an implementation to output the
       input-reply.

       It is recommended that implementations report an underflow as
       an exception and allow the input-reply to be resupplied.

16.  _R_E_A_D_ _A_N_D_ _R_E_S_T_O_R_E_ _S_T_A_T_E_M_E_N_T_S

 16.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       The read-statement provides for the assignment of values to
       variables from a sequence of data created from data-statements
       (see 17). The restore-statement allows the data in the program
       to be reread. The general syntactic forms of the read and re-
       store statements are

                 READ variable, ..., variable
                 RESTORE

 16.2  _S_y_n_t_a_x

       1. read-statement        = READ variable-list
       2. restore-statement     = RESTORE

 16.3  _E_x_a_m_p_l_e_s

       READ X, Y, Z           READ X(1), A$, C

 16.4  _S_e_m_a_n_t_i_c_s

       The read-statement causes variables in the variable-list to be
       assigned values, in order, from the sequence of data (see 17).
       A conceptual pointer is associated with the data sequence. At
       the initiation of execution of a program, this pointer points
       to the first datum in the data sequence. Each time a read-state-
       ment is executed, each variable in the variable-list in se-
       quence is assigned the value of the datum indicated by the point-
       er and the pointer is advanced to point beyond that datum.

       The restore-statement resets the pointer for the data sequence
       to the beginning of the sequence, so that the next read-state-
       ment executed will read data from the beginning of the sequence
       once again.

				 - 24 -
       The type of a datum in the data sequence shall correspond to
       the type of the variable to which it is to be assigned; i.e.,
       numeric-variables require unquoted-strings which are numeric-
       constants as data and string-variables require quoted-strings
       or unquoted-strings as data. An unquoted-string which is a
       valid numeric representation may be assigned to either a string-
       variable or a numeric-variable by a read-statement.

       If the evaluation of a numeric datum causes an underflow, then
       its value shall be replaced by zero.

       Subscript expressions in the variable-list are evaluated after
       values have been assigned to the variables preceding them (i.e.
       to the left of them) in the list.

 16.5  _E_x_c_e_p_t_i_o_n_s

       - The variable-list in a read-statement requires more data than
         are present in the remainder of the data-sequence (fatal).

       - An attempt is made to assign a string datum to a numeric
         variable (fatal).

       - The evaluation of a numeric datum causes an overflow (non-
         fatal, the recommended recovery procedure is to supply ma-
         chine infinity with the appropriate sign and continue).

       - A string datum contains too many characters (fatal).

 16.6  _R_e_m_a_r_k_s

       It is recommended that implementations report an underflow as
       exception and continue.

17.  _D_A_T_A_ _S_T_A_T_E_M_E_N_T

 17.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       The data-statement provides for the creation of a sequence of
       representations for data elements for use by the read-statement.
       The general syntactic form of the data-statement is

                DATA datum, ..., datum

       where each datum is either a numeric constant, a string-constant
       or an unquoted string.

 17.2  _S_y_n_t_a_x

       1. data-statement        = DATA data-list
       2. data-list             = datum (comma datum)*

 17.3  _E_x_a_m_p_l_e_s

       DATA 3.14159, PI, 5E-10, ","

 17.4  _S_e_m_a_n_t_i_c_s

       Data from the totality of data-statements in the program are
       collected into a single data sequence. The order in which data
       appear textually in the totality of all data-statements deter-
       mines the order of the data in the data sequence.

				 - 25 -

       If the execution of a program reaches a line containing a
       data-statement, then it shall proceed to the next line with
       no other effect.

 17.5  _E_x_c_e_p_t_i_o_n_s

       None.

18.  _A_R_R_A_Y_ _D_E_C_L_A_R_A_T_I_O_N_S

 18.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       The dimension-statement is used to reserve space for arrays.
       Unless declared otherwise, all array subscripts shall have a
       lower bound of zero and an upper bound of ten. Thus the default
       space allocation reserves space for 11 elements in one-dimen-
       sional arrays and 121 elements in two-dimensional arrays. By
       use of a dimension-statement, the subscript(s) of an array may
       be declared to have an upper bound other than ten. By use of
       an option-statement, the subscripts of all arrays may be de-
       clared to have a lower bound of one.

       The general syntactic form of the dimension-statement is

               DIM declaration, ..., declaration

       where each declaration has the form

               letter (integer)
       or      letter (integer , integer)

       The general syntactic form of the option-statement is

               OPTION BASE n

       where n is either 0 or 1.

 18.2  _S_y_n_t_a_x

       1. dimension-statement   = DIM array declaration
                                  (comma array-declaration)*
       2. array-declaration     = numeric-array-name left-parenthesis
                                  bounds right-parenthesis
       3. bounds                = integer (comma integer)?
       4. option-statement      = OPTION BASE (0/1)

 18.3  _E_x_a_m_p_l_e_s

       DIM A (6), B(10,10)

 18.4  _S_e_m_a_n_t_i_c_s

       Each array-declaration occurring in a dimension-statement de-
       clares the array named to be either one or two dimensional ac-
       cording to whether one or two bounds are listed for the array.
       In addition, the bounds specify the maximum values that sub-
       script expressions for the array can have.

       The declaration for an array, if present at all, shall occur in
       a lower numbered line than any reference to an element of that

				 - 26 -
       array. Arrays that are not declared in any dimension-statement
       are declared implicitly to be one or two dimensional according
       to their use in the program, and to have subscripts with a
       maximum value of ten (see 7).

       The option-statement declares the minimum value for all array
       subscripts; if no option-statement occurs in a program, this
       minimum is zero. An option-statement, if present at all, must
       occur in a lower numbered line than any dimension-statement or
       any reference to an element of an array. If an option-statement
       specifies that the lower bound for array subscripts is one, then
       no dimension-statement in the program may specify an upper bound
       of zero. A program may contain at most one option-statement.

       If the execution of a program reaches a line containing a di-
       mension-statement or an option-statement, then it shall pro-
       ceed to the next line with no other effect.

       An array can be explicitly dimensioned only once.

 18.5  _E_x_c_e_p_t_i_o_n_s

       None.

19.  _R_E_M_A_R_K_ _S_T_A_T_E_M_E_N_T

 19.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       The remark-statement allows program annotation.

 19.2  _S_y_n_t_a_x

       1. remark-statement      = rem remark-string

 19.3  _E_x_a_m_p_l_e_s

       REM FINAL CHECK

 19.4  _S_e_m_a_n_t_i_c_s

       If the execution of a program reaches a line containing a
       remark-statement, then it shall proceed to the next line with
       no other effect.

 19.5  _E_x_c_e_p_t_i_o_n_s

       None.

20.  _R_A_N_D_O_M_I_Z_E_ _S_T_A_T_E_M_E_N_T

 20.1  _G_e_n_e_r_a_l_ _D_e_s_c_r_i_p_t_i_o_n

       The randomize-statement overrides the implementation-predefined
       sequence of pseudo-random numbers as values for the RND func-
       tion, allowing different (and unpredictable) sequences each
       time a given program is executed.

 20.2  _S_y_n_t_a_x

       1. randomize-statement   = RANDOMIZE

 20.3  _E_x_a_m_p_l_e_s

       RANDOMIZE

				 - 27 -
 20.4  _S_e_m_a_n_t_i_c_s

       Execution of the randomize-statement shall generate a new un-
       predictable starting point for the list of pseudo-random num-
       bers used by the RND function (see 9).

 20.5  _E_x_c_e_p_t_i_o_n_s

       None.

 20.6  _R_e_m_a_r_k_s

       In the case of implementations which do not have access to a
       randomizing device such as a real-time clock, the randomize-
       statement may be implemented by means of an interaction with
       the user.

				 - 28 -

       +---------------------------------------+---------------+
       |            NAME                       |    GRAPHIC    |
       +---------------------------------------+---------------+
       |                                       |               |
       | Space                                 |               |
       | Exclamation-mark                      |       !       |
       | Quotation-mark                        |       "       |
       | Number-sign                           |       #       |
       | Dollar-sign                           |       $       |
       | Percent-sign                          |       %       |
       | Ampersand                             |       &       |
       | Apostrophe                            |       '       |
       | Left-parenthesis                      |       (       |
       | Right-parenthesis                     |       )       |
       | Asterisk                              |       *       |
       | Plus-sign                             |       +       |
       | Comma                                 |       ,       |
       | Minus-sign                            |       -       |
       | Full-stop                             |       .       |
       | Solidus                               |       /       |
       | Digits                                |     0 - 9     |
       | Colon                                 |       :       |
       | Semi-colon                            |       ;       |
       | Less-than-sign                        |       <       |
       | Equals-sign                           |       =       |
       | Greater-than-sign                     |       >       |
       | Question-mark                         |       ?       |
       | Letters                               |     A - Z     |
       | Circumflex-accent                     |       ^       |
       | Underline                             |       _       |
       +---------------------------------------+---------------+

				TABLE 1

				 - 29 -

                    +---+---+---+---+---+---+---+---+
                   b|0  |0  |0  |0  |1  |1  |1  |1  |
                    +---+---+---+---+---+---+---+---+
                   b| 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 |
                    +---+---+---+---+---+---+---+---+
        b b b b    b|  0|  1|  0|  1|  0|  1|  0|  1|
       +-+-+-+-+    +---+---+---+---+---+---+---+---+
       |0|0|0|0|    | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
       +=+=+=+=+====+===+===+===+===+===+===+===+===+
       |0|0|0|0| 0  |NUL|DLE| SP| 0 | @ | P | ` | p |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |0|0|0|1| 1  |SOH|DC1| ! | 1 | A | Q | a | q |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |0|0|1|0| 2  |STX|DC2| " | 2 | B | R | b | r |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |0|0|1|1| 3  |ETX|DC3| # | 3 | C | S | c | s |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |0|1|0|0| 4  |EDT|DC4| $ | 4 | D | T | d | t |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |0|1|0|1| 5  |ENQ|NAK| % | 5 | E | U | e | u |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |0|1|1|0| 6  |ACK|SYN| & | 6 | F | V | f | v |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |0|1|1|1| 7  |BEL|ETB| ' | 7 | G | W | g | w |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |1|0|0|0| 8  | BS|CAN| ( | 8 | H | X | h | x |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |1|0|0|1| 9  | HT| EM| ) | 9 | I | Y | i | y |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |1|0|1|0| 10 | LF|SUB| * | : | J | Z | j | z |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |1|0|1|1| 11 | VT|ESC| + | ; | K | [ | k | { |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |1|1|0|0| 12 | FF| FS| , | < | L | \ | l | | |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |1|1|0|1| 13 | CR| GS| - | = | M | ] | m | } |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |1|1|1|0| 14 | SO| RS| . | > | N | ^ | n | ~ |
       +-+-+-+-+----+---+---+---+---+---+---+---+---+
       |1|1|1|1| 15 | SI| US| / | ? | O | _ | o |DEL|
       +-+-+-+-+----+---+---+---+---+---+---+---+---+

				TABLE 2

NOTE: In the 7-bit and in the 8-bit code tables two characters
      are allocated to pos. 2/4, namely $ and box.  In any version
      of the codes a single character is to be allocated to this
      position. The character of the 7-bit or of the 8-bit coded
      character set, which corresponds to the character $ of the
      Minimal BASIC character set is either $ or box (box in the
      International Reference Version).

      The same applies to pos. 2/3 for the characters £ and #,
      the latter being the character of the International Refer-
      ence version.

				 - 30 -

			       _A_P_P_E_N_D_I_X_ _1

		      Organization of the Standard
		      ----------------------------

This Standard is organized into a number of sections, each of which
covers a particular feature of BASIC. Sections 4 to 20 are divided
into sub-sections, as follows.

Sub-section 1.  General Description

This sub-section briefly describes the features of BASIC to be treat-
ed and indicates the general syntactic form of these features.

Sub-section 2.  Syntax

The exact syntax of features of the language is described in a modi-
fied context-free grammar or Backus-Naur   Form. The details of this
method of syntax specification are described in Appendix 2.

In order to keep the syntax reasonably simple the syntax specifica-
tion will allow it to describe some constructions which, strictly
speaking, are not legal according to this Standard, e.g. it will
allow the generation of the statement

          100 LET X = A(1) + A(1,2)

in which the array A occurs with differing numbers of subscripts.
Rather than ruling such constructions out by a more complicated syn-
tax, this Standard shall instead rule them out in the semantics.

Sub-section 3.  Examples

A short list of valid examples that can be generated by certain of
the syntax equations in sub-section 2 is given.

Sub-section 4.  Semantics

The semantic rules in this Standard serve two purposes. First, they
rule out certain constructions which are permitted by the syntax,
but which have no valid meaning according to this Standard. Second,
they assign a meaning to the remaining constructions.

Sub-section 5.  Exceptions

An exception occurs when an implementation recognizes that a program
may not perform or is not performing in accordance with this Standard.
All exceptions described in this section shall be reported unless
some mechanism is provided in an enhancement to this Standard that
has been invoked by the user to handle exceptions.

Where indicated, certain exceptions may be handled by the specified
procedures; if no procedure is given, or if restrictions imposed by

				 - 31 -

the hardware or the operating environment make it impossible to
follow the given procedures, then the exception must be handled by
terminating the program. Enhancements to this Standard may describe
mechanisms for controlling the manner in which exceptions are re-
ported and handled, but no such mechanisms are specified in this
Standard.

This Standard does not specify an order in which exceptions shall
be detected or processed.

Sub-section 6.  Remarks

This sub-section contains remarks which point out certain features
of this Standard as well as remarks which make recommendations con-
cerning the implementation of a BASIC language processor in an oper-
ating environment.

				 - 32 -

			       _A_P_P_E_N_D_I_X_ _2

		     Method of Syntax Specification
		     ------------------------------

The syntax, through a series of rewriting rules known as "product-
ions", defines syntactic objects of various types, such as "program"
or "expression", and describes which strings of symbols are objects
of these types.

In the syntax, upper-case letters, digits, and (possibly hyphenated)
lower-case words are used as "metanames", i.e. as names of syntactic
objects. Most of these metanames are defined by rewriting rules in
terms of other metanames. In order that this process terminate, cer-
tain metanames are designated as "terminal" metanames, and rewriting
rules for them are not included in the syntax. All terminal metanames
occur for the first time and are defined in Section 4. It should be
noted in particular that all upper-case letters are terminal meta-
names which denote themselves.

We illustrate further details of the syntax by considering some ex-
amples. In Section 12 we find the production

           gosub-statement = GO space* SUB line-number

which indicates that a "gosub-statement" consists of the letters G,
O, any number of spaces, S, U, and B followed by a line number.

What is a "line-number"? In Section 5, the production

           line-number = digit digit? digit? digit?

indicates that a "line-number" is a "digit" followed by up to three
other "digits" (the question mark is a syntactic operator indicating
that the object it follows may or may not be present).

What is a "digit"? In Section 4, the production

           digit = 0 / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9

indicates that a "digit" is either a "0", a "1", ... or a "9" (the
solidus is a syntactic operator meaning "or" and is used to indicate
that a metaname can be rewritten in one of several ways). Since the
digits are terminal metanames (i.e. they do not occur on the left-
hand side of any production), our decipherment of the syntax for the
"gosub-statement" comes to an end. The semantics in Section 4 iden-
tify the digits in terms of the characters they represent.

An asterisk is a syntactic operator like the question-mark, and it
indicates that the object it follows may occur any number of times,
including zero times, in the production.

For example
           integer = digit digit*

indicates than an "integer" is a "digit" followed by an arbitrary

				 - 33 -

number of other "digits".

Parentheses may be used to group sequences of metanames together.
For example
            variable-list = variable (comma variable)*

defines a "variable-list" to consist of a "variable" followed by an
arbitrary number of other "variables" separated by "commas".

When several syntactic operators occur in the same production, the
operators "?" and "*" take precedence over the operator "/".

Spaces in the syntax are used to separate hyphenated lower-case words
from each other. Special conventions are observed regarding spaces
in BASIC programs (see Section 5). The syntax as described generates
programs which contain no spaces other than those occurring in re-
marks, in certain string constants, or where the presence of a space
is explicitly indicated by the metaname "space".

Additional spaces may be inserted to improve readability provided
that the restrictions imposed in Section 5 are observed.

- 34 -

			      _A_P_P_E_N_D_I_X_ _3

			      _C_o_n_f_o_r_m_a_n_c_e

There are two aspects of conformance to this language Standard :
conformance by a program written in the language, and conformance
by an implementation which processes such programs.

A program is said to conform to this Standard only when

- each statement contained therein is a syntactically valid instance
  of a statement specified in this Standard,

- each statement has an explicitly valid meaning specified herein,

  and

- the totality of statements compose an instance of a valid program
  which has an explicitly valid meaning specified herein.

An implementation is said to conform to this Standard only when

- it accepts and processes programs conforming to this Standard,

- it reports reasons for rejecting any program which does not conform
  to this Standard,

- it interprets errors and exceptional circumstances according to the
  specifications of this Standard,

- its interpretation of the semantics of each statement of a stand-
  ard-conforming program conforms to the specification in this
  Standard.

- its interpretation of the semantics of a standard-conforming pro-
  gram as a whole conforms to the specifications in this Standard,

- it accepts as input, manipulates, and can generate as output numbers
  of at least the precision and range specified in this Standard, and

- it is accompanied by a reference manual which clearly defines the
  actions taken in regard to features which are called "undefined"
  or "implementation-defined" in this Standard.

This Standard does not include requirements for reporting specific
syntactic errors in the text of a program. Implementations conforming
to this Standard my accept programs written in an enhanced language
without having to report all constructs not conforming to this Stand-
ard. However, whenever a statement or other program element does not
conform to the syntactic rules given herein, either an error shall
be reported or the statement or other program element shall have an
implementation-defined meaning.

				 - 35 -

			       _A_P_P_E_N_D_I_X_ _4



		    Implementation-defined Features
                    -------------------------------

A number of the features defined in this Standard have been left
for definition by the implementor. However, this will not affect
portability, provided that the limits recommended in the various
sections are respected. The way these features are implemented
shall be defined in the user- or system-manual of the specific
implementation.

The following is a list of implementation-defined features:

- accuracy of evaluation of numeric expressions (see 8)

- end-of-line (see 5, 14 and 15)

- exrad-width for printing numeric representations (see 14)

- initial value of variables (see 7)

- input-prompt (see 15)

- longest string that can be retained (see 11)

- value of machine infinitesimal (see 6)

- value of machine infinity (see 6)

- margin for output lines (see 14)

- precision for numeric values (see 6)

- print-zone length (see 14)

- pseudo-random number sequence (see 9 and 20)

- significance width for printing numeric representations (see 15)

- means of requesting the input-reply in batch mode (see 15)

