[mercury-users] typeclass constraint on type definition... wrong

[Robert Bossy]

Hello,

I tried the following

:- typeclass foo(T) where [].
:- type bar(T) ---> bar(T) <= foo(T).


I meant a declaration of the type bar, parametric on the type variable T since T is an instance of typeclass foo.
And it didn't work...
Is it semantically wrong? If not how to write it?

The error is "undefined type foo/1"... so what does

:- type foo(T) ---> foo(T).
:- type bar(T) ---> bar(T) <= foo(T).

mean?



Thanks,

Robert Bossy
bossy at ccr.jussieu.fr


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