Re: [ooc-compiler] FOR Loops And Structured Variables

[Frank C. <fj...@th...>]

August Karlstrom wrote:

> Why doesn't the following module compile?
> 
>    MODULE Test;
>       VAR a: ARRAY 1 OF LONGINT;
>    BEGIN
>       FOR a[0] := 0 TO 1 DO END
>    END Test.
> 
> I've read that in Modula, loop variables in FOR loops cannot come from 
> structured variables, but I can't find that restriction in the Oberon-2 
> report. Anyway, what's the motivation for the restriction?

 From the Oberon-2 Report:

     ForStatement = FOR ident ":=" Expression TO Expression
                    [BY ConstExpression] DO StatementSequence END.

and 'ident' is defined as:

   1. Identifiers are sequences of letters and digits. The first character
   must be a letter.

     ident = letter {letter | digit}.

   Examples:     x     Scan     Oberon2     GetSymbol     firstLetter

This obviously excludes structured variables as loop variables.

Motivation? You would have to ask Wirth or Gutnecht about that, but my guess 
would be disbelief that anyone sensible would use anything other than a 
simple integer variable as a loop variable.

-- 

TONY RANDALL!  Is YOUR life a PATIO of FUN??