\begin{code}
module FunDeps (
+ Equation, pprEquation, pprEquationDoc,
oclose, grow, improve, checkInstFDs, checkClsFD, pprFundeps
) where
#include "HsVersions.h"
-import Var ( TyVar )
+import Name ( getSrcLoc )
+import Var ( Id, TyVar )
import Class ( Class, FunDep, classTvsFds )
-import Type ( Type, ThetaType, PredType(..), predTyUnique, tyVarsOfTypes, tyVarsOfPred )
import Subst ( mkSubst, emptyInScopeSet, substTy )
-import Unify ( unifyTyListsX )
-import Outputable ( Outputable, SDoc, interppSP, ptext, empty, hsep, punctuate, comma )
+import TcType ( Type, ThetaType, SourceType(..), PredType,
+ predTyUnique, mkClassPred, tyVarsOfTypes, tyVarsOfPred,
+ unifyTyListsX, unifyExtendTysX, tcEqType
+ )
+import PprType ( )
import VarSet
import VarEnv
+import Outputable
import List ( tails )
+import Maybes ( maybeToBool )
import ListSetOps ( equivClassesByUniq )
\end{code}
-- In our example, tv_fds will be [ ({x,y}, {z}), ({x,p},{q}) ]
-- Meaning "knowing x,y fixes z, knowing x,p fixes q"
tv_fds = [ (tyVarsOfTypes xs, tyVarsOfTypes ys)
- | Class cls tys <- preds, -- Ignore implicit params
+ | ClassP cls tys <- preds, -- Ignore implicit params
let (cls_tvs, cls_fds) = classTvsFds cls,
fd <- cls_fds,
let (xs,ys) = instFD fd cls_tvs tys
\begin{code}
grow :: [PredType] -> TyVarSet -> TyVarSet
grow preds fixed_tvs
- | null pred_sets = fixed_tvs
- | otherwise = loop fixed_tvs
+ | null preds = fixed_tvs
+ | otherwise = loop fixed_tvs
where
loop fixed_tvs
| new_fixed_tvs `subVarSet` fixed_tvs = fixed_tvs
\begin{code}
----------
-type Equation = (Type,Type) -- These two types should be equal
- -- INVARIANT: they aren't already equal
+type Equation = (TyVarSet, Type, Type) -- These two types should be equal, for some
+ -- substitution of the tyvars in the tyvar set
+ -- For example, ({a,b}, (a,Int,b), (Int,z,Bool))
+ -- We unify z with Int, but since a and b are quantified we do nothing to them
+ -- We usually act on an equation by instantiating the quantified type varaibles
+ -- to fresh type variables, and then calling the standard unifier.
+ --
+ -- INVARIANT: they aren't already equal
+ --
+
+
+pprEquationDoc (eqn, doc) = vcat [pprEquation eqn, nest 2 doc]
+
+pprEquation (qtvs, t1, t2) = ptext SLIT("forall") <+> braces (pprWithCommas ppr (varSetElems qtvs))
+ <+> ppr t1 <+> ptext SLIT(":=:") <+> ppr t2
----------
-improve :: InstEnv a -- Gives instances for given class
- -> [PredType] -- Current constraints
- -> [Equation] -- Derived equalities that must also hold
+improve :: InstEnv Id -- Gives instances for given class
+ -> [(PredType,SDoc)] -- Current constraints; doc says where they come from
+ -> [(Equation,SDoc)] -- Derived equalities that must also hold
-- (NB the above INVARIANT for type Equation)
+ -- The SDoc explains why the equation holds (for error messages)
type InstEnv a = Class -> [(TyVarSet, [Type], a)]
-- This is a bit clumsy, because InstEnv is really
\begin{code}
improve inst_env preds
- = [ eqn | group <- equivClassesByUniq predTyUnique preds,
+ = [ eqn | group <- equivClassesByUniq (predTyUnique . fst) preds,
eqn <- checkGroup inst_env group ]
----------
-checkGroup :: InstEnv a -> [PredType] -> [Equation]
+checkGroup :: InstEnv Id -> [(PredType,SDoc)] -> [(Equation, SDoc)]
-- The preds are all for the same class or implicit param
-checkGroup inst_env (IParam _ ty : ips)
+checkGroup inst_env (p1@(IParam _ ty, _) : ips)
= -- For implicit parameters, all the types must match
- [(ty, ty') | IParam _ ty' <- ips, ty /= ty']
+ [ ((emptyVarSet, ty, ty'), mkEqnMsg p1 p2)
+ | p2@(IParam _ ty', _) <- ips, not (ty `tcEqType` ty')]
-checkGroup inst_env clss@(Class cls tys : _)
+checkGroup inst_env clss@((ClassP cls _, _) : _)
= -- For classes life is more complicated
-- Suppose the class is like
-- classs C as | (l1 -> r1), (l2 -> r2), ... where ...
- -- Then FOR EACH PAIR (Class c tys1, Class c tys2) in the list clss
+ -- Then FOR EACH PAIR (ClassP c tys1, ClassP c tys2) in the list clss
-- we check whether
-- U l1[tys1/as] = U l2[tys2/as]
-- (where U is a unifier)
-- NOTE that we iterate over the fds first; they are typically
-- empty, which aborts the rest of the loop.
- pairwise_eqns :: [(Type,Type)]
+ pairwise_eqns :: [(Equation,SDoc)]
pairwise_eqns -- This group comes from pairwise comparison
- = [ eqn | fd <- cls_fds,
- Class _ tys1 : rest <- tails clss,
- Class _ tys2 <- rest,
- eqn <- checkClsFD emptyVarSet fd cls_tvs tys1 tys2
+ = [ (eqn, mkEqnMsg p1 p2)
+ | fd <- cls_fds,
+ p1@(ClassP _ tys1, _) : rest <- tails clss,
+ p2@(ClassP _ tys2, _) <- rest,
+ eqn <- checkClsFD emptyVarSet fd cls_tvs tys1 tys2
]
- instance_eqns :: [(Type,Type)]
+ instance_eqns :: [(Equation,SDoc)]
instance_eqns -- This group comes from comparing with instance decls
- = [ eqn | fd <- cls_fds,
- (qtvs, tys1, _) <- cls_inst_env,
- Class _ tys2 <- clss,
- eqn <- checkClsFD qtvs fd cls_tvs tys1 tys2
+ = [ (eqn, mkEqnMsg p1 p2)
+ | fd <- cls_fds,
+ (qtvs, tys1, dfun_id) <- cls_inst_env,
+ let p1 = (mkClassPred cls tys1,
+ ptext SLIT("arising from the instance declaration at") <+> ppr (getSrcLoc dfun_id)),
+ p2@(ClassP _ tys2, _) <- clss,
+ eqn <- checkClsFD qtvs fd cls_tvs tys1 tys2
]
-
+mkEqnMsg (pred1,from1) (pred2,from2)
+ = vcat [ptext SLIT("When using functional dependencies to combine"),
+ nest 2 (sep [ppr pred1 <> comma, nest 2 from1]),
+ nest 2 (sep [ppr pred2 <> comma, nest 2 from2])]
+
----------
-checkClsFD :: TyVarSet -- The quantified type variables, which
- -- can be instantiated to make the types match
+checkClsFD :: TyVarSet -- Quantified type variables; see note below
-> FunDep TyVar -> [TyVar] -- One functional dependency from the class
-> [Type] -> [Type]
-> [Equation]
checkClsFD qtvs fd clas_tvs tys1 tys2
+-- 'qtvs' are the quantified type variables, the ones which an be instantiated
+-- to make the types match. For example, given
+-- class C a b | a->b where ...
+-- instance C (Maybe x) (Tree x) where ..
+-- and an Inst of form (C (Maybe t1 t2),
+-- then we will call checkClsFD with
+--
+-- qtvs = {x}, tys1 = [Maybe x, Tree x]
+-- tys2 = [Maybe t1, t2]
+--
+-- We can instantiate x to t1, and then we want to force
+-- Tree x [t1/x] :=: t2
+
-- We use 'unify' even though we are often only matching
-- unifyTyListsX will only bind variables in qtvs, so it's OK!
= case unifyTyListsX qtvs ls1 ls2 of
Nothing -> []
- Just unif -> [(sr1, sr2) | (r1,r2) <- rs1 `zip` rs2,
- let sr1 = substTy full_unif r1,
- let sr2 = substTy full_unif r2,
- sr1 /= sr2]
+ Just unif -> -- pprTrace "checkFD" (vcat [ppr_fd fd,
+ -- ppr (varSetElems qtvs) <+> (ppr ls1 $$ ppr ls2),
+ -- ppr unif]) $
+ [ (qtvs', substTy full_unif r1, substTy full_unif r2)
+ | (r1,r2) <- rs1 `zip` rs2,
+ not (maybeToBool (unifyExtendTysX qtvs unif r1 r2))]
+ -- Don't include any equations that already hold
+ -- taking account of the fact that any qtvs that aren't
+ -- already instantiated can be instantiated to anything at all
+ -- NB: qtvs, not qtvs' because unifyExtendTysX only tries to
+ -- look template tyvars up in the substitution
where
full_unif = mkSubst emptyInScopeSet unif
-- No for-alls in sight; hmm
+
+ qtvs' = filterVarSet (\v -> not (v `elemSubstEnv` unif)) qtvs
+ -- qtvs' are the quantified type variables
+ -- that have not been substituted out
where
(ls1, rs1) = instFD fd clas_tvs tys1
(ls2, rs2) = instFD fd clas_tvs tys2
projects / ghc-hetmet.git / blobdiff