On Mon, Sep 02, 2002 at 03:11:58AM -0700, Ashley Yakeley wrote: > At 2002-09-02 02:46, Jerzy Karczmarczuk wrote: > > >class Module v s | v->s . > ... > >instance Num s => Module (v->s) s > ... > >instance ...=> Module ((v->s)->(v->s)) s > ... > >But GHCi yells that two instances in view of the functional > >dependency declared are in conflict. > > GHCi is correct. Bear in mind GHC ignores contexts in instance > declarations when calculating conflicts. This is unfortunate, but > apparently fixing it would be hard.
Even taking contexts into account, these two might still conflict: if you had instance Num ((v->s)->v) for some values of v and s, you would get a conflict. GHC (and Hugs) check for potential conflicts like this unless you explicitly allow overlapping instances. --Dylan
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