2 module TcImprove ( tcImprove ) where
4 #include "HsVersions.h"
7 import Class ( Class, FunDep, className, classExtraBigSig )
8 import Unify ( unifyTyListsX, matchTys )
9 import Subst ( mkSubst, substTy )
10 import TcEnv ( tcGetInstEnv, classInstEnv )
12 import TcType ( TcType, TcTyVar, TcTyVarSet, zonkTcType, zonkTcTypes )
13 import TcUnify ( unifyTauTyLists )
14 import Inst ( LIE, Inst, LookupInstResult(..),
15 lookupInst, getFunDepsOfLIE, getIPsOfLIE,
16 zonkLIE, zonkFunDeps {- for debugging -} )
17 import VarSet ( VarSet, emptyVarSet, unionVarSet )
18 import VarEnv ( emptyVarEnv )
19 import FunDeps ( instantiateFdClassTys )
21 import List ( elemIndex, nub )
25 tcImprove :: LIE -> TcM s ()
26 -- Do unifications based on functional dependencies in the LIE
28 = tcGetInstEnv `thenNF_Tc` \ inst_env ->
30 nfdss, clas_nfdss, inst_nfdss, ip_nfdss :: [(TcTyVarSet, Name, [FunDep TcType])]
31 nfdss = ip_nfdss ++ clas_nfdss ++ inst_nfdss
33 cfdss :: [(Class, [FunDep TcType])]
34 cfdss = getFunDepsOfLIE lie
35 clas_nfdss = [(emptyVarSet, className c, fds) | (c,fds) <- cfdss]
37 classes = nub (map fst cfdss)
38 inst_nfdss = [ (free, className c, instantiateFdClassTys c ts)
40 (free, ts, i) <- classInstEnv inst_env c
43 ip_nfdss = [(emptyVarSet, n, [([], [ty])]) | (n,ty) <- getIPsOfLIE lie]
46 class C a b c | a->b where ...
49 Given the LIE FD C (Int->t)
50 we get clas_nfdss = [({}, C, [Int->t, t->Int])
51 inst_nfdss = [({c}, C, [Int->Bool, Bool->Int])]
53 Another way would be to flatten a bit
54 we get clas_nfdss = [({}, C, Int->t), ({}, C, t->Int)]
55 inst_nfdss = [({c}, C, Int->Bool), ({c}, C, Bool->Int)]
57 iterImprove then matches up the C and Int, and unifies t <-> Bool
64 iterImprove :: [(VarSet, Name, [FunDep TcType])] -> TcM s ()
65 iterImprove [] = returnTc ()
67 = selfImprove pairImprove cfdss `thenTc` \ change2 ->
68 if {- change1 || -} change2 then
73 -- ZZ this will do a lot of redundant checking wrt instances
74 -- it would do to make this operate over two lists, the first
75 -- with only clas_nfds and ip_nfds, and the second with everything
76 -- control would otherwise mimic the current loop, so that the
77 -- caller could control whether the redundant inst improvements
79 -- you could then also use this to check for consistency of new instances
81 -- selfImprove is really just doing a cartesian product of all the fds
82 selfImprove f [] = returnTc False
83 selfImprove f (nfds : nfdss)
84 = mapTc (f nfds) nfdss `thenTc` \ changes ->
85 selfImprove f nfdss `thenTc` \ rest_changed ->
86 returnTc (or changes || rest_changed)
88 pairImprove (free1, n1, fds1) (free2, n2, fds2)
90 checkFds (free1 `unionVarSet` free2) fds1 fds2
94 checkFds free [] [] = returnTc False
95 checkFds free (fd1 : fd1s) (fd2 : fd2s) =
96 checkFd free fd1 fd2 `thenTc` \ change ->
97 checkFds free fd1s fd2s `thenTc` \ changes ->
98 returnTc (change || changes)
99 --checkFds _ _ = returnTc False
101 checkFd free (t_x, t_y) (s_x, s_y)
102 -- we need to zonk each time because unification
103 -- may happen at any time
104 = zonkUnifyTys free t_x s_x `thenTc` \ msubst ->
107 let t_y' = map (substTy (mkSubst emptyVarEnv subst)) t_y
108 s_y' = map (substTy (mkSubst emptyVarEnv subst)) s_y
110 zonkEqTys t_y' s_y' `thenTc` \ eq ->
112 -- they're the same, nothing changes...
115 -- ZZ what happens if two instance vars unify?
116 unifyTauTyLists t_y' s_y' `thenTc_`
117 -- if we get here, something must have unified
123 = mapTc zonkTcType ts1 `thenTc` \ ts1' ->
124 mapTc zonkTcType ts2 `thenTc` \ ts2' ->
125 returnTc (ts1' == ts2')
127 zonkMatchTys ts1 free ts2
128 = mapTc zonkTcType ts1 `thenTc` \ ts1' ->
129 mapTc zonkTcType ts2 `thenTc` \ ts2' ->
130 -- pprTrace "zMT" (ppr (ts1', free, ts2')) $
131 case matchTys free ts2' ts1' of
132 Just (subst, []) -> -- pprTrace "zMT match!" empty $
133 returnTc (Just subst)
134 Nothing -> returnTc Nothing
136 zonkUnifyTys free ts1 ts2
137 = mapTc zonkTcType ts1 `thenTc` \ ts1' ->
138 mapTc zonkTcType ts2 `thenTc` \ ts2' ->
139 -- pprTrace "zMT" (ppr (ts1', free, ts2')) $
140 case unifyTyListsX free ts2' ts1' of
141 Just subst -> returnTc (Just subst)
142 Nothing -> returnTc Nothing