NAME

Syntax - Pod file describing syntax understood by Language::Basic module

SYNOPSIS

There is no Language::Basic::Syntax module. This is just a pod file describing the syntax that's supported by the Language::Basic module.

DESCRIPTION

Things in italics are objects. Things in boldface are actual strings (reserved words or punctuation). "[]" means optional, "..." means optionally more copies of the same thing, and things between slashes that look like Perl regexps are Perl regexps.

This syntax description probably isn't exactly correct from a computer science standpoint, but the idea is just to show what LB supports.

Line Syntax

Line:

Line_Num Statement [: Statement ...]

Statement Syntax

• DATA Constant [ , Constant ...]

• DIM Var-Name [ Arglist ] [ , Var-Name [ Arglist ] ...]

  Arglist must be made up of constant arithmetic expressions.

• DEF Func-Name ( Var-Name [ , Var-Name ...] ) = Arith-Exp

  Var-Names must be scalar variables.

• END

• FOR Lvalue = Arith-Exp TO Arith-Exp [ STEP Arith-Exp]

• GOTO Arith-Exp

• IF Or-Exp THEN Statement [ : Statement ...] [ ELSE Statement [ : Statement ...]]

  IF Or-Exp THEN Line_Num [ ELSE Line_Num ]

• INPUT [ Str-Const ; ] Lvalue [ , Lvalue ...]

• [LET] Lvalue = Arith-Exp

• NEXT Lvalue

• ON Arith-Exp GOTO/GOSUB Arith-Exp [ , Arith-Exp ...]

• PRINT [ Expression [ Print_Sep ] [ Expression [ Print_Sep ] ...] ]

• READ Lvalue [ , Lvalue ...]

• Comment

Expression Syntax

Note that, unlike C or Perl, Boolean values cannot be "cast" to non-Boolean (string or numeric) values and vice versa.

By the way, the classes in module Language::Basic::Expression rather closely mimic this syntax description.

Expression:

Arith-Exp

Or-Exp

Arithmetic Expression:

Mult-Exp Arith-Op Mult-Exp

String-Exp + String-Exp

Multiplicative Expression:

Unary-Exp Mult-Op Unary-Exp

Unary Expression:

- Unary-Exp

(Arith-Exp)

Lvalue

Function

Constant

Lvalue:

Var-Name [ Arglist ]

Arglist:

( Expression [ , Expression ...] )

Function:

Func-Name Arglist

Constant:

Str-Const

Num-Const

String Expression:

Str-Const

Arith-Exp

The Arith-Exp must be made from Str-Exps.

Logical Or Expression:

And-Exp [ OR Or-Exp ]

Logical And Expression:

Rel-Exp [ AND And-Exp ]

Relational Expression:

NOT Rel-Exp

Arith-Exp Rel-Op Arith-Exp

String-Exp Rel-Op String-Exp

( Or-Exp )

Identifier Syntax

Variable Name:

Numeric Identifier

String Identifier

Function Name:

/FN[A-Z]\w+/

Numeric Identifier:

/[A-Z]\w*/

String Identifier:

/[A-Z]\w*\$/

Token Syntax

Tokens, or atoms, are indivisible pieces of text making up a BASIC program

(Note: Language::Basic only pays attention to case in string constants.)

Line Number:

/\d+/

Comment:

REM /.*/

Note that a comment goes all the way to the end of a line. Colons in a comment do not start a new statement.

Keyword:

DATA | DIM | DEF | END | FOR | GOSUB | GOTO | IF | INPUT | LET | NEXT | ON | PRINT | READ | RETURN | THEN | ELSE | TO | STEP

Numeric Constant:

/(\d*)?\.?\d+/

String Constant:

/".*?"/

Relational Operator:

< | <= | > | >= | = | <>

Arithmetic Operator:

+ | -

Multiplicative Operator:

* | /

Print Separator:

, | ;