[mercury-users] Re: State variable problem

[Nicholas Nethercote]

On Wed, 31 May 2006, Nicholas Nethercote wrote:

>  type_of(app(Name, Args), app(Name, NArgs), Pos, GSyms, LSyms, !Errs) = T :-
>      T = type_of_app(call, Name, Args, NArgs, Pos, GSyms, LSyms, !Errs).
>
> I get this error message about it:
>
>  typecheck.m:918: In clause for function `typecheck.type_of/7':
>  typecheck.m:918:   warning: variable `Errs' occurs only once in this scope.
>
> I don't see what the problem is.  But if I replace the "!Errs" in the call 
> with "!.Errs, !:Errs", viz:
>
>  type_of(app(Name, Args), app(Name, NArgs), Pos, GSyms, LSyms, !Errs) = T :-
>    T = type_of_app(call, Name, Args, NArgs, Pos, GSyms, LSyms, !.Errs, 
> !:Errs).
>
> I don't get the error.

Oh, I see:  you're not allowed to use !Errs in a function application.

Nick
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