[m-users.] Determinism Woes...

[M McDonough]

> To paraphrase Neo, "I know Prolog".

> but I don't know Mercury and I am struggling to figure out this error....I
> am porting some old SWI code and it boils down to the fact that I obvuisly
> don't truly understand what "det" means! Here is the code both as discrete
> disjunctive clauses and a single big disjunct:
>
> :- pred char_type(char::in, chartype::out) is det.
>
> char_type(')', p_open).
> char_type('(', p_close).
> char_type(_, c_general).
>
> char_type(C, T) :-
>    (
>         C = '(', T = p_open
>     ;   C = ')', T = p_close
>     ;   C = _,   T = c_general
>     ).

What you probably want is to use if/then/conditionals instead of a
disjunction. When Mercury sees the C = _, you're telling it that literally
all characters should yield c_general, including the characters '(' and
')'. That means that for the inputs of ( and ), there are two solutions.
Both the p_* solution, and c_general.

If you also have those rules above, then you're also doubling the solutions
(which you won't want to do in most situations).
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