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Simon Peyton Jones authored
which (finally) fills out the functionality of polymorphic kinds. It also fixes numerous bugs. Main changes are: Renaming stuff ~~~~~~~~~~~~~~ * New type in HsTypes: data HsBndrSig sig = HsBSig sig [Name] which is used for type signatures in patterns, and kind signatures in types. So when you say f (x :: [a]) = x ++ x or data T (f :: k -> *) (x :: *) = MkT (f x) the signatures in both cases are a HsBndrSig. * The [Name] in HsBndrSig records the variables bound by the pattern, that is 'a' in the first example, 'k' in the second, and nothing in the third. The renamer initialises the field. * As a result I was able to get rid of RnHsSyn.extractHsTyNames :: LHsType Name -> NameSet and its friends altogether. Deleted the entire module! This led to some knock-on refactoring; in particular the type renamer now returns the free variables just like the term renamer. Kind-checking types: mainly TcHsType ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A major change is that instead of kind-checking types in two passes, we now do one. Under the old scheme, the first pass did kind-checking and (hackily) annotated the HsType with the inferred kinds; and the second pass desugared the HsType to a Type. But now that we have kind variables inside types, the first pass (TcHsType.tc_hs_type) can go straight to Type, and zonking will squeeze out any kind unification variables later. This is much nicer, but it was much more fiddly than I had expected. The nastiest corner is this: it's very important that tc_hs_type uses lazy constructors to build the returned type. See Note [Zonking inside the knot] in TcHsType. Type-checking type and class declarations: mainly TcTyClsDecls ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ I did tons of refactoring in TcTyClsDecls. Simpler and nicer now. Typechecking bindings: mainly TcBinds ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ I rejigged (yet again) the handling of type signatures in TcBinds. It's a bit simpler now. The main change is that tcTySigs goes right through to a TcSigInfo in one step; previously it was split into two, part here and part later. Unsafe coercions ~~~~~~~~~~~~~~~~ Usually equality coercions have exactly the same kind on both sides. But we do allow an *unsafe* coercion between Int# and Bool, say, used in case error Bool "flah" of { True -> 3#; False -> 0# } --> (error Bool "flah") |> unsafeCoerce Bool Int# So what is the instantiation of (~#) here? unsafeCoerce Bool Int# :: (~#) ??? Bool Int# I'm using OpenKind here for now, but it's un-satisfying that the lhs and rhs of the ~ don't have precisely the same kind. More minor ~~~~~~~~~~ * HsDecl.TySynonym has its free variables attached, which makes the cycle computation in TcTyDecls.mkSynEdges easier. * Fixed a nasty reversed-comparison bug in FamInstEnv: @@ -490,7 +490,7 @@ lookup_fam_inst_env' match_fun one_sided ie fam tys n_tys = length tys extra_tys = drop arity tys (match_tys, add_extra_tys) - | arity > n_tys = (take arity tys, \res_tys -> res_tys ++ extra_tys) + | arity < n_tys = (take arity tys, \res_tys -> res_tys ++ extra_tys) | otherwise = (tys, \res_tys -> res_tys)
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