X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypes%2FInstEnv.lhs;h=1abcc183849cae9bb20323b1ff56bd99b29fb9b1;hp=9cb68c80e5dcb19535db16072095dc8b4dfe61aa;hb=ad94d40948668032189ad22a0ad741ac1f645f50;hpb=eb2bf7ad9f967861da2e19ff71a80428c7c2df28 diff --git a/compiler/types/InstEnv.lhs b/compiler/types/InstEnv.lhs index 9cb68c8..1abcc18 100644 --- a/compiler/types/InstEnv.lhs +++ b/compiler/types/InstEnv.lhs @@ -7,6 +7,13 @@ The bits common to TcInstDcls and TcDeriv. \begin{code} +{-# OPTIONS -w #-} +-- The above warning supression flag is a temporary kludge. +-- While working on this module you are encouraged to remove it and fix +-- any warnings in the module. See +-- http://hackage.haskell.org/trac/ghc/wiki/CodingStyle#Warnings +-- for details + module InstEnv ( DFunId, OverlapFlag(..), Instance(..), pprInstance, pprInstanceHdr, pprInstances, @@ -134,7 +141,7 @@ pprInstance :: Instance -> SDoc -- Prints the Instance as an instance declaration pprInstance ispec@(Instance { is_flag = flag }) = hang (pprInstanceHdr ispec) - 2 (ptext SLIT("--") <+> (pprDefnLoc (getSrcLoc ispec))) + 2 (ptext SLIT("--") <+> (pprDefnLoc (getSrcSpan ispec))) -- * pprInstanceHdr is used in VStudio to populate the ClassView tree pprInstanceHdr :: Instance -> SDoc @@ -385,20 +392,41 @@ the env is kept ordered, the first match must be the only one. The thing we are looking up can have an arbitrary "flexi" part. \begin{code} -lookupInstEnv :: (InstEnv -- External package inst-env - ,InstEnv) -- Home-package inst-env - -> Class -> [Type] -- What we are looking for - -> ([(TvSubst, Instance)], -- Successful matches - [Instance]) -- These don't match but do unify - -- The second component of the tuple happens when we look up - -- Foo [a] - -- in an InstEnv that has entries for - -- Foo [Int] - -- Foo [b] - -- Then which we choose would depend on the way in which 'a' - -- is instantiated. So we report that Foo [b] is a match (mapping b->a) - -- but Foo [Int] is a unifier. This gives the caller a better chance of - -- giving a suitable error messagen +type InstTypes = [Either TyVar Type] + -- Right ty => Instantiate with this type + -- Left tv => Instantiate with any type of this tyvar's kind + +type InstMatch = (Instance, InstTypes) +\end{code} + +Note [InstTypes: instantiating types] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +A successful match is an Instance, together with the types at which + the dfun_id in the Instance should be instantiated +The instantiating types are (Mabye Type)s because the dfun +might have some tyvars that *only* appear in arguments + dfun :: forall a b. C a b, Ord b => D [a] +When we match this against D [ty], we return the instantiating types + [Right ty, Left b] +where the Nothing indicates that 'b' can be freely instantiated. +(The caller instantiates it to a flexi type variable, which will presumably + presumably later become fixed via functional dependencies.) + +\begin{code} +lookupInstEnv :: (InstEnv, InstEnv) -- External and home package inst-env + -> Class -> [Type] -- What we are looking for + -> ([InstMatch], -- Successful matches + [Instance]) -- These don't match but do unify + +-- The second component of the result pair happens when we look up +-- Foo [a] +-- in an InstEnv that has entries for +-- Foo [Int] +-- Foo [b] +-- Then which we choose would depend on the way in which 'a' +-- is instantiated. So we report that Foo [b] is a match (mapping b->a) +-- but Foo [Int] is a unifier. This gives the caller a better chance of +-- giving a suitable error messagen lookupInstEnv (pkg_ie, home_ie) cls tys = (pruned_matches, all_unifs) @@ -409,10 +437,11 @@ lookupInstEnv (pkg_ie, home_ie) cls tys (pkg_matches, pkg_unifs) = lookup pkg_ie all_matches = home_matches ++ pkg_matches all_unifs = home_unifs ++ pkg_unifs - pruned_matches - | null all_unifs = foldr insert_overlapping [] all_matches - | otherwise = all_matches -- Non-empty unifs is always an error situation, - -- so don't attempt to pune the matches + pruned_matches = foldr insert_overlapping [] all_matches + -- Even if the unifs is non-empty (an error situation) + -- we still prune the matches, so that the error message isn't + -- misleading (complaining of multiple matches when some should be + -- overlapped away) -------------- lookup env = case lookupUFM env cls of @@ -427,6 +456,12 @@ lookupInstEnv (pkg_ie, home_ie) cls tys -> find [] [] insts -------------- + lookup_tv :: TvSubst -> TyVar -> Either TyVar Type + -- See Note [InstTypes: instantiating types] + lookup_tv subst tv = case lookupTyVar subst tv of + Just ty -> Right ty + Nothing -> Left tv + find ms us [] = (ms, us) find ms us (item@(Instance { is_tcs = mb_tcs, is_tvs = tpl_tvs, is_tys = tpl_tys, is_flag = oflag, @@ -436,7 +471,11 @@ lookupInstEnv (pkg_ie, home_ie) cls tys = find ms us rest | Just subst <- tcMatchTys tpl_tvs tpl_tys tys - = find ((subst,item):ms) us rest + = let + (dfun_tvs, _) = tcSplitForAllTys (idType dfun) + in + ASSERT( all (`elemVarSet` tpl_tvs) dfun_tvs ) -- Check invariant + find ((item, map (lookup_tv subst) dfun_tvs) : ms) us rest -- Does not match, so next check whether the things unify -- See Note [overlapping instances] above @@ -476,8 +515,7 @@ bind_fn tv | isTcTyVar tv && isExistentialTyVar tv = Skolem -- on the grounds that the correct instance depends on the instantiation of 'a' --------------- -insert_overlapping :: (TvSubst, Instance) -> [(TvSubst, Instance)] - -> [(TvSubst, Instance)] +insert_overlapping :: InstMatch -> [InstMatch] -> [InstMatch] -- Add a new solution, knocking out strictly less specific ones insert_overlapping new_item [] = [new_item] insert_overlapping new_item (item:items) @@ -493,7 +531,7 @@ insert_overlapping new_item (item:items) new_beats_old = new_item `beats` item old_beats_new = item `beats` new_item - (_, instA) `beats` (_, instB) + (instA, _) `beats` (instB, _) = overlap_ok && isJust (tcMatchTys (is_tvs instB) (is_tys instB) (is_tys instA)) -- A beats B if A is more specific than B, and B admits overlap