Re: Dropping some misfeatures in for-loops and `absolute' variables

One can handle nested for loops with REPEAT and WHILE loops, without going into FOR loop contortions:

From a Delphi program I wrote long ago. By using dynamic arrays, you can get around a fixed dimension.

unit ForLoopUnit;

interface

uses Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;

type TForm1 = class(TForm) private { Private declarations } public { Public declarations } end;

var Form1: TForm1;

implementation {$R *.DFM}

const Dim = 3;

type TIndex = array[1..Dim] of Integer;

var F: TextFile; Index, LowerBound, UpperBound: TIndex;

procedure Initialize;

var K: Integer;

begin for K := 1 to Dim do begin LowerBound[K] := 0; UpperBound[K] := 5; //Random(6) + 1; end; end; // Initialize

procedure P(const Index: TIndex); // for testing

var K: Integer; S: string;

begin S := 'Index = ['; for K := 1 to Dim - 1 do S := S + IntToStr(Index[K]) + ', '; S := S + IntToStr(Index[Dim]) + ']'; Writeln(F, S); end; // P

procedure MultiForLoop;

var K: Integer;

begin Index := LowerBound; K := Dim; repeat P(Index); while (K >= 1) and (Index[K] = UpperBound[K]) do Dec(K); if K = 0 then Break; // repeat loop // K >= 1, Index[K] < UpperBound[K], // and Index[J] < UpperBound[J] for all J > K Inc(Index[K]); Inc(K); while K <= Dim do begin Index[K] := LowerBound[K]; Inc(K) end; until False; end;

initialization AssignFile(F, 'For.Pas'); Rewrite(F); Initialize; MultiForLoop; CloseFile(F); end.

Harley Flanders

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Frank D. Engel, Jr. wrote:

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On Jun 29, 2005, at 2:19 AM, Frank Heckenbach wrote:

...

GPC accepts the following program, but produces quite silly results:

program Foo;

var a: array [1 .. 2] of Integer value (0, 0); i: Integer;

begin i := 1; for a[i] := 1 to 10 do begin WriteLn (i, ' ', a[i]); if a[i] = 5 then i := 2 end end.

The problem is that it evaluates the index i each time, not once before the loop. It would be possible to fix it, but do we really want that? Neither BP nor CP/EP allow it, they allow only identifiers in for-loops.

Waldek and I see no need for such a feature. (If it made it possible to nest a compile-time-unknown number of `for' loops, I could see some point, but of course, it doesn't.)

Actually, I think it does (untested, though):

CONST max_depth = 100;

FUNCTION Multi_For(depth, limit : INTEGER) : LONGINT; VAR i : INTEGER; a : ARRAY[1..max_depth] OF INTEGER; v : LONGINT;

BEGIN { setup } i := 1; v := 0;

{ the loops }
FOR a[i] := 1 TO limit DO BEGIN
    IF (i < depth) THEN BEGIN
        INC(i);
        a[i] := 1
    END ELSE BEGIN
        { actual loop stuff }
        v := v + a[i];

        { handle reduction in depth at end of loop }
        IF (a[i] = limit) AND (i > 1) THEN
            DEC(i)
    END
END;

Multi_For := v

END;

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Frank D. Engel, Jr. fde101@fjrhome.net

$ ln -s /usr/share/kjvbible /usr/manual $ true | cat /usr/manual | grep "John 3:16" John 3:16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life. $ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (Darwin)

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