
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 knockon refactoring; in particular the type renamer now returns the free variables just like the term renamer. Kindchecking types: mainly TcHsType ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A major change is that instead of kindchecking types in two passes, we now do one. Under the old scheme, the first pass did kindchecking 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. Typechecking 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 unsatisfying 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 reversedcomparison 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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