[m-users.] String comparison when compiling to C

[Sean Charles (emacstheviking)]

Hi Richard,

All sorted thanks, I already had `string` imported. I think working with Python has dulled my brain sometimes.
The Mercury `way` is a much better fit for how I intend to work it going forward, I am writing a strongly typed FORTH with Mercury as a rapid application tool for another project.

I have this code now, so far, but eventually I plan to support all the Mercury numerical types, different bases etc as FORTH allows, it won't be a strict standards compliant FORTH but rather, my interpretation of it guided by Mercury...

%
% Comparison operators.
%
core("<",           stack('<')).

:- pred '<'(opstate::in, opstate::out, dstk::in, dstk::out) is det.
    % [ V2, V1 ] <=> ( n1 n2 -- flag ) ie TOS is n2, is V1, global rule!
'<'(!Mode, !Stk) :-
    ( if [ V2, V1 | Rest ] = !.Stk then
        !:Stk = Rest,
        ( if V1 = int(N1), V2 = int(N2) then
            ( if compare(<, N1, N2)
            then push_true(!Mode, !Stk)
            else push_false(!Mode, !Stk)
            )
        else if V1 = str(S1), V2 = str(S2) then
            trace [io(!IO)] (
                io.format("> %s %s\n", [s(string(V1)),s(string(V2))],!IO)
            ),
            ( if compare(<, S1, S2)
            then push_true(!Mode, !Stk)
            else push_false(!Mode, !Stk)
            )
        else
            seterr("> requires two objects of the same type.", !Mode)
        )
    else stkerr(">", 2, !.Stk, !Mode)).

Once all the types I want are in the above code, then I will find a way to reduce the code, `compare/3` is great in that respect as it is a uniform interface across types.

I hope to find a way to generalise the call to `compare/3`, I will experiment!!! As much as Mercury sometimes makes my head want to explode at times, I can't help thinking that if the worldf at large used it, the world might be a better place, well, at least less global tech issues, e.g. Crowdstrike.

It's a bunch of fun so far at times (sarcasm emoji) but what else would one be doing?

Thanks again,
Sean.


> On 24 Aug 2024, at 06:56, Richard O'Keefe <raoknz at gmail.com> wrote:
> 
> Does
> :- import_module string.
> ...
>    compare(>, S1, S2)
> 
> work for you?
> 
> On Sat, 24 Aug 2024 at 02:53, Sean Charles (emacstheviking)
> <objitsu at gmail.com> wrote:
>> 
>> 
>> % The builtin comparison operation on strings is also implementation
>> % dependent. The current implementation performs string comparison using
>> %
>> % - C's strcmp() function, when compiling to C;
>> 
>> Guided by the text, "The builtin comparison operation on strings "... I assumed that >, <, >= etc would work fork string types but my code:
>> 
>>    615 op_greater_than(!Mode, !Stk) :-
>>    616     ( if [ V1, V2 | Rest ] = !.Stk then
>>    617         !:Stk = Rest,
>>    618
>>    619         ( if V1 = int(N1), V2 = int(N2) then
>>    620             trace [io(!IO)] (
>>    621                 io.format("> %s %s\n", [s(string(V1)),s(string(V2))],!IO)
>>    622             ),
>>    623             ( if N1 > N2
>>    624             then push_true(!Mode, !Stk)
>>    625             else push_false(!Mode, !Stk)
>>    626             )
>>    627
>>    628         else if V1 = str(S1), V2 = str(S2) then
>>    629             trace [io(!IO)] (
>>    630                 io.format("> %s %s\n", [s(string(V1)),s(string(V2))],!IO)
>>    631             ),
>>    632             ( if S1 > S2
>>    633             then push_true(!Mode, !Stk)
>>    634             else push_false(!Mode, !Stk)
>>    635             )
>>    636         else
>>    637             seterr("> requires two objects of the same type.", !Mode)
>> 
>> gets these errors:
>> 
>> dstack.m:632: In clause for predicate `op_greater_than'/4:
>> dstack.m:632:   in call to predicate `int.>'/2:
>> dstack.m:632:   in argument 1:
>> dstack.m:632:     variable `S1' has type
>> dstack.m:632:       string,
>> dstack.m:632:     expected type was
>> dstack.m:632:       int;
>> dstack.m:632:   in argument 2:
>> dstack.m:632:     variable `S2' has type
>> dstack.m:632:       string,
>> dstack.m:632:     expected type was
>> dstack.m:632:       int.
>> 
>> 
>> So what is the 'way' to do string comparisons? I find it odd in all the code I've written, I have never needed to do this before!
>> 
>> Thanks,
>> Sean.
>> 
>> _______________________________________________
>> users mailing list
>> users at lists.mercurylang.org
>> https://lists.mercurylang.org/listinfo/users

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