[m-users.] How to user filter_map with a nondet function

[Razetime]

My main question here is "how do I use a nondet predicate inside a
semidet predicate and make it infer as semidet"? changing the mode to
nondet and semidet both don't work, which is why i asked.

On 11/20/22, Volker Wysk <post at volker-wysk.de> wrote:
> Hi
>
> When calling a predicate, the modes must match one of the mode lines of the
> predicate. Since filter_map has only one mode/mode line, the passed
> predicate must match that. This means that the passed predicate must be
> semidet, not cc_nondet.
>
> You might be able to copy the source code of the filter_map predicate,
> rename it to, say, filter_map_1 and add a second mode line, with the
> determinism category cc_nondet of the higher order argument.
>
> However, I don't understand what a cc_nondet predicate would do. I've never
> seen it be used that way. Of course, you can just try it out.
>
> Cheers,
> Volker
>
>
> Am Samstag, dem 19.11.2022 um 22:58 +0530 schrieb Razetime:
>> :- module a10.
>>
>> :- interface.
>> :- import_module io.
>> :- pred main(io::di,io::uo) is det.
>>
>> :- implementation.
>> :- import_module alib.
>> :- import_module list,string,int,char.
>>
>> :- pred go(int::out,int::out,cl::in,cl::out) is nondet.
>> go(X,Y) --> l("value "),num(X),l(" goes to bot "),num(Y).
>>
>> :- pred give(int::out,int::out,int::out,cl::in,cl::out) is nondet.
>> give(X,Y,Z) --> l("bot "),num(X),l(" gives low to bot "),num(Y),l("
>> and high to "),num(Z).
>>
>> main(!IO):-
>>   rlinesc("inp/10",L0,!IO),
>>   filter_map((pred(X::in,{Y,Z}::out) is cc_nondet:-
>>     go(Y,Z,X,[])
>>   ),L0,As,Mo),
>>   print_line(As,!IO)
>>   .
>>
>> alib is here: https://github.com/razetime/aoc/blob/main/16/alib.m
>>
>> I'm trying to use the DCG `go` with filter_map to parse lines which
>> satisfy the predicate. I get the following error:
>>
>> Making Mercury/int3s/a10.int3
>> Making Mercury/ints/a10.int
>> Making Mercury/cs/a10.c
>> For more information, recompile with `-E'.
>> a10.m:019: In clause for `main(di, uo)':
>> a10.m:019:   in argument 1 of call to predicate `list.filter_map'/4:
>> a10.m:019:   mode error: variable `V_14' has instantiatedness
>> a10.m:019:     /* unique */ (pred(in, out) is cc_nondet),
>> a10.m:019:   expected instantiatedness was `(pred(in, out) is semidet)'.
>> a10.m:019: In clause for predicate `main'/2:
>> a10.m:019:   warning: variable `Mo' occurs only once in this scope.
>> ** Error making `Mercury/cs/a10.c'.
>>
>> I do understand that I can change num(X) in alib.m, but I would like
>> to know if i can make the determinism check succeed in other ways.
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>
>