[m-users.] Multi predicate of entire enum
sheganinans at gmail.com
Mon Jul 20 16:00:04 AEST 2020
Very nice Julien!
I just went ahead and went the code generation way. Already works, based
off of some code I wrote a while ago to do some Mercury codegen.
I like this solution a lot, very straightforward and does exactly what I
thought should be possible within type_desc and construct but wasn't sure
On Sun, Jul 19, 2020 at 10:27 PM Julien Fischer <jfischer at opturion.com>
> On Sun, 19 Jul 2020, Ace wrote:
> > So say I have some enum:
> > `:- type ex ---> a; b; c.`
> > And I want to generate a function similar to:
> > ```
> > :- pred ex_mul(ex::out) is multi.
> > ex_mul(a).
> > ex_mul(b).
> > ex_mul(c).
> > ```
> > Any kind of standard library predicate I can use so I don't have to
> > add a new case to the predicate for every instance of the enum?
> You could use RTTI to implement such a predicate, although it will be more
> expensive than than the simple form above, e.g. something like:
> :- pred ex_mul(ex::out) is multi.
> ex_mul(V) :-
> TypeDesc = type_desc.type_of(V),
> NumFunctors = construct.det_num_functors(TypeDesc),
> ( if
> int.nondet_int_in_range(0, NumFunctors - 1, FunctorNum),
> Univ = construct.construct(TypeDesc, FunctorNum, )
> univ.det_univ_to_type(Univ, V)
> error("should not get here")
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