Commit 7fde87b3 authored by simonpj's avatar simonpj
Browse files

[project @ 2001-07-25 15:55:30 by simonpj]

-----------------------------------------
	Fix a bug in the monomorphism restriction
	------------------------------------------

Thanks for Koen for reporting this bug.

In tcSimplifyRestricted, I wrongly called tcSimpifyToDicts,
whereas actually we have to simplfy further than simply to
a dictionary.

The test for this is in typecheck/should_compile/tc132.hs
parent 92428681
......@@ -722,16 +722,22 @@ tcSimplifyRestricted doc tau_tvs wanted_lie
-- foo = f (3::Int)
-- We want to infer the polymorphic type
-- foo :: forall b. b -> b
tcSimplifyToDicts wanted_lie `thenTc` \ (dicts, _) ->
let
constrained_tvs = tyVarsOfInsts dicts
wanteds = lieToList wanted_lie
try_me inst = ReduceMe -- Reduce as far as we can. Don't stop at
-- dicts; the idea is to get rid of as many type
-- variables as possible, and we don't want to stop
-- at (say) Monad (ST s), because that reduces
-- immediately, with no constraint on s.
in
simpleReduceLoop doc try_me wanteds `thenTc` \ (_, _, constrained_dicts) ->
-- Next, figure out the tyvars we will quantify over
zonkTcTyVarsAndFV (varSetElems tau_tvs) `thenNF_Tc` \ tau_tvs' ->
tcGetGlobalTyVars `thenNF_Tc` \ gbl_tvs ->
let
qtvs = (tau_tvs' `minusVarSet` oclose (predsOfInsts dicts) gbl_tvs)
constrained_tvs = tyVarsOfInsts constrained_dicts
qtvs = (tau_tvs' `minusVarSet` oclose (predsOfInsts constrained_dicts) gbl_tvs)
`minusVarSet` constrained_tvs
in
......@@ -752,7 +758,7 @@ tcSimplifyRestricted doc tau_tvs wanted_lie
reduceContext doc try_me [] wanteds' `thenTc` \ (no_improvement, frees, binds, irreds) ->
ASSERT( no_improvement )
ASSERT( null irreds )
-- No need to loop because tcSimplifyToDicts will have
-- No need to loop because simpleReduceLoop will have
-- already done any improvement necessary
returnTc (varSetElems qtvs, mkLIE frees, binds)
......
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