🚀 go-pugleaf

In <91003.102704BJ020000@NDSUVM1.BITNET> BJ020000@NDSUVM1.BITNET (Dave Mueller) writes:


>I'm trying to write a FOR loop that needs a 'nonconstant' BY, for example:

>IF Case = 1 THEN
>   Begin := 0;
>   End := Length(Line)-1;
>   By := 1;
>ELSE
>   Begin := Length(Line)-1;
>   End := 0;
>   By := -1;
>END;

>FOR Loop := Begin TO End BY By DO
>etc..


>Any suggestions as to how I go about doing this in a FOR Loop???  Or am I gonna
>end up doing it some other way??

My version of PIM (3rd corrected ed.) states:

(Page 158, "Report on The Programming Language Modula-2":)
9.8 For Statements
... Its [the variable's] value should not be changed by the statement
sequence.
... C [the increment/decrement] must be a constant of type INTEGER or
CARDINAL.

(Page 172, "Appendix 1, The Syntax of Modula-2":)
ForStatement = FOR ident ":=" expression TO expression
	[BY ConstExpression] DO StatementSequence END.
	    ^^^^^

So, Your pretty much out of luck. I see two possibilities:
1 You make it two FOR-statements with an IF-statement selecting between
  both (You could put it into the CASE)
2 Use a WHILE-statement:

	replace

  FOR Loop := Begin TO End BY By DO

	by

  Loop := Begin;
  WHILE Loop <= End DO
     <statements>
     INC(Loop, By);
  END;

>Thanx much!

>Dave Mueller

Josef Moellers
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