Language Definition – Constants

One final item before moving on to the implementation of the Parser. In the Parser, numeric constants are not signed. Any plus or minus sign will be treated as a unary operator as far as token parsing is concerned.  If later during translation, a constant has a unary operator, then it will be folded into the constant. The Parser and/or Translator can't assume that a plus or minus is part of the constant too soon, take the example A‑5, if the constant is ‑5, then this expression would have two tokens, A and ‑5, and would have no operator, which is an error.

Integer constants will be any numeric value that fits in an integer and does not have a decimal point. Double (floating point) constants will have a decimal point, an optional exponent (“e” or “E” followed by an optional sign and some digits), or will not fit in a integer. Integers will be 32‑bit values having a range of ‑2,147,483,648 to 2,147,483,647, however, since there is no sign, the value ‑2,147,483,648 is not possible. Double precision values have a range of approximately 1e‑308 to 1e+308.

String constants start and end with a double quote. There will also be an easy way of putting double quotes in a string constant because using "hello "+CHR$(34)+"world"+CHR$(34) is cumbersome and unintuitive. The C style like "hello \"world\"" (also used by xBasic) is not desirable either. TrueBasic's method is two double quotes like "hello ""world""" is probably the best solution, so that method will be used.

Language Definition – Subroutines

Subroutines are similar to functions except subroutines have no return value and therefore the identifier name does not have a data type symbol. The general syntax for a subroutine is:

    SUB sub_name(arguments)
   ...
    END SUB

The arguments will be optional. Arguments will be called by reference if a variable or array element is used as an argument, otherwise the arguments are by values. The arguments will be treated as local variables, except if called by reference, modifying the local variable was also modify the caller's variable or array element. The by reference call can be prevented by surrounding the argument in the function call by parentheses as in (A). Entire arrays can be passed by reference by using just the array name in the subroutine call.

Subroutines may call themselves recursively. It is up to the programmer to prevent an infinite loop, though eventually memory will run out as each subroutine call will increase the size of the stack.

The subroutine will return upon a RETURN statement or when the END SUB statement is reached. The SUB will not be executed upon reaching the SUB statement, execution will proceed to the after the END SUB statement. The subroutine will be called using a CALL statement as:

    CALL sub_name(arguments)

Updated Saturday January 2, 2010; 9:45am: Looks like most of the BASICs use just "SUB" for subroutine, so I decided to also use just SUB instead of SUBROUTINE.