[mercury-users] Re: Mercury Tutorial / Functions

[Goncalo Jorge Coelho e Silva]

> > read_strings_2(RevSs, Ss, IO0, IO) :-
> >         io__read_line_as_string(Result, IO0, IO1),
> >         (
> >                 Result = ok(S),
> >                 %io__write_string(S,IO0, IO1),
> >                 read_strings_2([S | RevSs], Ss, IO1, IO)
> >         ;
> >                 Result = eof,
> 
> Here I omitted the goal
> 
>                   IO     = IO1,
> 
> which is necessary to ensure that IO is instantiated (as we promise in
> the mode declaration) when read_strings_2/4 terminates.

Before:

inter.m:043: In clause for `read_strings_2(in, out, di, uo)':
inter.m:043:   mode error in conjunction. The next 3 error messages
inter.m:043:   indicate possible causes of this error.
inter.m:043: In clause for `read_strings_2(in, out, di, uo)':
inter.m:043:   mode mismatch in disjunction.
inter.m:043:   `IO' :: unique, free, not_reached.
inter.m:030: In clause for `read_strings_2(in, out, di, uo)':
inter.m:030:   in argument 2 of clause head:
inter.m:030:   mode error in unification of `HeadVar__2' and `Ss'.
inter.m:030:   Variable `HeadVar__2' has instantiatedness `free',
inter.m:030:   variable `Ss' has instantiatedness `free'.
inter.m:030: In clause for `read_strings_2(in, out, di, uo)':
inter.m:030:   in argument 4 of clause head:
inter.m:030:   mode error in unification of `HeadVar__4' and `IO'.
inter.m:030:   Variable `HeadVar__4' has instantiatedness `free',
inter.m:030:   variable `IO' has instantiatedness `free'.
make: *** [run] Error 1


After I inserted the goad 'IO = IO'  :

inter.m:024:   warning: variable `Ss' occurs only once in this scope.
inter.m:043: In clause for `read_strings_2(in, out, di, uo)':
inter.m:043:   mode error in conjunction. The next 3 error messages
inter.m:043:   indicate possible causes of this error.
inter.m:037: In clause for `read_strings_2(in, out, di, uo)':
inter.m:037:   in argument 3 of call to predicate
`inter:read_strings_2/4':
inter.m:037:   mode error: variable `IO1' has instantiatedness `ground',
inter.m:037:   expected instantiatedness was `unique'.
inter.m:030: In clause for `read_strings_2(in, out, di, uo)':
inter.m:030:   in argument 2 of clause head:
inter.m:030:   mode error in unification of `HeadVar__2' and `Ss'.
inter.m:030:   Variable `HeadVar__2' has instantiatedness `free',
inter.m:030:   variable `Ss' has instantiatedness `free'.
inter.m:030: In clause for `read_strings_2(in, out, di, uo)':
inter.m:030:   in argument 4 of clause head:
inter.m:030:   mode error in unification of `HeadVar__4' and `IO'.
inter.m:030:   Variable `HeadVar__4' has instantiatedness `free',
inter.m:030:   variable `IO' has instantiatedness `free'.


 Not only the problem persists, it still has this
to add:

inter.m:037:   mode error: variable `IO1' has instantiatedness `ground',
inter.m:037:   expected instantiatedness was `unique'.


 Reporting to the problem:

mode error in unification of `HeadVar__2' and `Ss'.
inter.m:030:   Variable `HeadVar__2' has instantiatedness `free',
inter.m:030:   variable `Ss' has instantiatedness `free'.

 I tried adding a goal 'forcing' the unification of Ss
(since it's said to be 'free', when it should be ground).
but it didn't do anything.

 Tips?

Thanks.

Cheers,
Goncalo
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