Hi Richard,
Thanks for looking into this!
On Mon, 9 Sep 2013, Richard Eisenberg wrote:
I took a look here and would like to help, but I'm confused: What makes
you think the dictionary for (Eq [b]) would be in scope? I can see where
the (Eq b) comes from (the theta that pops out of patSynSig), but where
does (Eq [b]) come from?
pattern P b b' = (MkT b b', ())
f (P x y) = [x] == [y]
I thought when I call 'thing_inside' in tcPatSynPat, it would (eventually)
get to typechecking the right-hand side, which has a dependency on (Eq
[b]). I thought this dependency is captured somewhere around here so that
it(s solution) can be added to the pat_binds field of the ConPatOut.
Otherwise, I don't see where it should be created -- and as you can see
from the warning emitted by GHC, it is assumed later on to be there:
WARNING: file compiler/coreSyn/CoreSubst.lhs, line 272
CoreSubst.lookupIdSubst simpleOptExpr $dEq_an7{v} [lid]
InScope [(00, wild_00{v} [lid]), (X6, wild_X6{v} [lid]),
(Xb, wild_Xb{v} [lid]), (amr, x{v amr} [lid]),
(ams, y{v ams} [lid]), (amR, b{tv amR} [tv]),
(an5, $dEq_an5{v} [lid]), (an8, cobox_an8{v} [lid]),
(dnk, ds_dnk{v} [lid]), (dnl, ds_dnl{v} [lid]),
(dnm, ds_dnm{v} [lid]), (dnr, cobox{v dnr} [lid]),
(rgK, main:ConstrEx.f{v rgK} [lidx])]
here, $dEq_an5 is (Eq b), and $dEq_an7 is (Eq [b]).
So it seems the emitted core expects this (Eq [b]) to be there (bound to
the parametrised instance (Eq[] (Eq b))).
Thanks,
Gergo
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