[M3devel] subrange value not constant?

[Mika Nystrom]

Martin, you have one bug: you don't initialize count.  Per 2.6.9 in the
Green Book, NEW returns "an arbitrary value of its type"

Also, for slightly more clarity, count can be a REF ARRAY OF CARDINAL.

INC and DEC would make the code a bit easier to read, perhaps.

Finally, you can dispense with min and max completely by just using
min, initialized to a[0], and re-allocating the array whenever the
new value is greater than min + NUMBER(count^) :-)  But maybe you
already know what min and max are by some means that doesn't involve
scanning the array.

    Mika




Martin Bishop writes:
>By the way, in case anyone cares, here's the proper code:
>
>PROCEDURE Sort(VAR a: ARRAY OF INTEGER; min, max: INTEGER) =
>  VAR range := max - min + 1;
>      count := NEW(REF ARRAY OF INTEGER, range);
>      z := 0;
>  BEGIN
>    FOR i := FIRST(a) TO LAST(a) DO
>      count[a[i] - min] := count[a[i] - min] + 1;
>    END;
>    FOR i := min TO max DO
>      WHILE (count[i - min] > 0) DO
>        a[z] := i;
>        INC(z);
>        count[i - min] := count[i - min] - 1;
>      END;
>    END;
>  END Sort;
>
>Martin Bishop wrote:
>> I've written this procedure (an implementation of counting sort):
>>
>> PROCEDURE Sort(VAR a: ARRAY OF INTEGER; min, max: INTEGER) =
>>  VAR count := ARRAY [min..max] OF INTEGER {0, ..};
>>      z := 0;
>>  BEGIN
>>    FOR i := FIRST(a) TO LAST(a) DO
>>      count[i - min] := count[i - min] + 1;
>>    END;
>>    FOR i := min TO max DO
>>      WHILE count[i - min] > 0 DO
>>        a[z] := i;
>>        INC(z);
>>        count[i - min] := count[i - min] - 1;
>>      END;
>>    END;
>>  END Sort;
>>
>> However, when I try to compile I get:
>>
>> "../Counting.m3", line 8: subrange lower bound is not constant
>> "../Counting.m3", line 8: subrange upper bound is not constant
>>
>> Line 8 is:
>>
>> VAR count := ARRAY [min..max] OF INTEGER {0, ..};
>>
>> I don't see what's wrong?
>>
>>