Re: [m-users.] Problem with DCG producing false negative

Volker Wysk <[email protected]> Mon, 17 Oct 2022 10:52:02 +0200

Newsgroups	gmane.comp.lang.mercury.general
Message-ID	<[email protected]>

Hi

I don't fully understand what you're doing here. But you should try to make
the DCG rules det or semidet. Then you can let the compiler spot your
errors, when it doesn't agree with the determinism category which you have
declared.

Hope that helps,
Volker


Am Montag, dem 17.10.2022 um 00:14 +0530 schrieb Razetime:
> I have created the following predicate tls to match lines that satisfy
> the conditions given in Advent of Code Day 7:
> https://adventofcode.com/2016/day/7 (Spoilers)
> 
> For some reason during testing ,the DCG fails when given
> L="fslvgbiibdkhchajyb[zpbhqrokrbfuqrowop]gqqzoqvfsdfcjcdurrs[xhqfcfytbbekivnvod]jxjwuxivnyhppvfhaol[evfnrmrjnnhychtpv]emiyjcjsnojxexs",
> tls(X,Y,to_char_list(L),[])
> and I am not sure why it is giving that result. What is done wrong here?
> 
> :- pred tls(list(cl)::out,list(cl)::out,cl::in,cl::out) is nondet.
> tls([X],[])        --> {alp(X)},seq(X).
> tls([X0|X],[Y0|Y]) --> {alp(X0),alp(Y0),\+abba(Y0)},
> 
> seq(X0),['['],seq(Y0),[']'],tls(X,Y),{any_true(abba,[X0|X])}.
> 
> :- pred seq(list(T),list(T),list(T)).
> :- mode seq(out,in,out) is multi.
> seq([])     --> [].
> seq([E|Es]) --> [E], seq(Es).
> 
> :- pred alp(cl::in) is semidet.
> alp(L):-all_true(is_alpha,L).
> 
> :- pred abba(cl::in) is semidet.
> abba([A,B,B,A|L]):-A\=B.
> abba([_,A,B,C|L]):-abba([A,B,C|L]).
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