[Oberon] Eliminating RETURN statements

[Hans Klaver]

Hi Jörg,

Thanks for your prompt reply.

> Here my proposals to make you code examples simpler:
> 
>      (* Oberon-07 *)
>      PROCEDURE F (x, y: INTEGER): INTEGER;
>        IF x < y THEN x := y – x 
>        ELSE x := x – y 
>        END
>      RETURN x
>      END F;
> 
> In this special case, this is perhaps a little clearer (
>      PROCEDURE F (x, y: INTEGER): INTEGER; RETURN ABS(x-y) END F;

Brilliant!
Inline ABS(x - y) is even clearer (and faster).
It illustrates that the example chosen by prof. Wirth can hardly be called 'real world' ;-)

> Your code
>      (* Oberon-07, right output *)
>      PROCEDURE Fit (i, j: INTEGER): BOOLEAN;
>        VAR k: INTEGER; OK: BOOLEAN;
>      BEGIN 
>        k := 0; OK := TRUE;
>        WHILE (k <= piecemax[i]) & OK DO
>          IF p[i][k] THEN 
>            IF puzzl[j + k] THEN OK := FALSE END
>          END;
>          INC(k)
>        END
>      RETURN OK
>      END Fit;
> 
> My proposal:
>      PROCEDURE Fit (i, j: INTEGER): BOOLEAN;
>        VAR k: INTEGER; OK: BOOELAN;
>      BEGIN 
>        k := 0;
>        WHILE (k <= piecemax[i]) DO
>           OK :=  ~( p[i, k] & puzzl[j + k] ); INC(k)
>        END
>      RETURN OK END Fit;

At first sight to me it looked like a correct rewrite.
Unfortunately this code leads to an "array index out of bounds" runtime exception (Trap 1 in System Oberon) of the puzzl array.

> Your code:
>      (* Oberon-07 *)
>      (...)
>        k := j;  res := 0;  exit := FALSE;
>        WHILE (k <= size) & (~ exit) DO
>          IF ~ puzzl[k] THEN res := k; exit := TRUE
>          ELSE INC(k)
>          END
>        END
>      RETURN res
>      END Place;
> 
> My proposal:
>        k := j;
>        WHILE (k <= size) & puzzl[k] DO INC(k) END;
>        IF k > size THEN k := 0 END
>      RETURN k
>      END Place;

This certainly is an elegant simplification.


Thanks again!

--
Hans Klaver