[mercury-users] Translating from Prolog

[Fergus Henderson]

On 10-Jun-2004, hanberg at ruc.dk <hanberg at ruc.dk> wrote:
> I hope it went well at the contest!
> 
> I'm still not on track, so if you would help me to a working example I will be
> more than greatfull since I have used quite a bit of time that I don't really
> have on it.
> 
> I'm trying this:
> 
> :- type &(A, B) ---> A & B.
> :- type ~(A) ---> ~(A).

You need "&" and "~" to be constructors for the same type.
So I think you want instead something like this:

	:- type expr ---> atomic_expr(...)
			; (expr & expr)
			; ~(expr).

with some appropriate stuff in the "..." part.
Or alternatively, use parametric polymorphism:

	:- type expr(T) ---> atomic_expr(T)
			; (expr(T) & expr(T))
			; ~(expr(T)).

> :- pred closes(_).

That should be

	:- pred closes(expr).

or

	:- pred closes(expr(T)).

depending on which solution you chose from the above.

-- 
Fergus Henderson                    |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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