%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[TcPatSyn]{Typechecking pattern synonym declarations}
\begin{code}
module TcPatSyn (tcPatSynDecl) where
import HsSyn
import TcPat
import TcRnMonad
import TcEnv
import TcMType
import TysPrim
import Name
import SrcLoc
import PatSyn
import NameSet
import Panic
import Outputable
import FastString
import Var
import Id
import IdInfo( IdDetails( VanillaId ) )
import TcBinds
import BasicTypes
import TcSimplify
import TcType
import VarSet
import Data.Monoid
import Bag
import TcEvidence
import BuildTyCl
import TypeRep
#include "HsVersions.h"
\end{code}
\begin{code}
tcPatSynDecl :: Located Name
-> HsPatSynDetails (Located Name)
-> LPat Name
-> HsPatSynDir Name
-> TcM (PatSyn, LHsBinds Id)
tcPatSynDecl lname@(L _ name) details lpat dir
= do { traceTc "tcPatSynDecl {" $ ppr name $$ ppr lpat
; tcCheckPatSynPat lpat
; pat_ty <- newFlexiTyVarTy openTypeKind
; let (arg_names, is_infix) = case details of
PrefixPatSyn names -> (map unLoc names, False)
InfixPatSyn name1 name2 -> (map unLoc [name1, name2], True)
; ((lpat', args), wanted) <- captureConstraints $
tcPat PatSyn lpat pat_ty $
mapM tcLookupId arg_names
; let named_taus = (name, pat_ty):map (\arg -> (getName arg, varType arg)) args
; traceTc "tcPatSynDecl::wanted" (ppr named_taus $$ ppr wanted)
; (qtvs, req_dicts, _mr_bites, ev_binds) <- simplifyInfer True False named_taus wanted
; (ex_vars, prov_dicts) <- tcCollectEx lpat'
; let univ_tvs = filter (not . (`elemVarSet` ex_vars)) qtvs
ex_tvs = varSetElems ex_vars
prov_theta = map evVarPred prov_dicts
req_theta = map evVarPred req_dicts
; univ_tvs <- mapM zonkQuantifiedTyVar univ_tvs
; ex_tvs <- mapM zonkQuantifiedTyVar ex_tvs
; prov_theta <- zonkTcThetaType prov_theta
; req_theta <- zonkTcThetaType req_theta
; pat_ty <- zonkTcType pat_ty
; args <- mapM zonkId args
; traceTc "tcPatSynDecl: ex" (ppr ex_tvs $$
ppr prov_theta $$
ppr prov_dicts)
; traceTc "tcPatSynDecl: univ" (ppr univ_tvs $$
ppr req_theta $$
ppr req_dicts $$
ppr ev_binds)
; let theta = prov_theta ++ req_theta
; traceTc "tcPatSynDecl: type" (ppr name $$
ppr univ_tvs $$
ppr (map varType args) $$
ppr pat_ty)
; (matcher_id, matcher_bind) <- tcPatSynMatcher lname lpat' args
univ_tvs ex_tvs
ev_binds
prov_dicts req_dicts
prov_theta req_theta
pat_ty
; m_wrapper <- tcPatSynWrapper lname lpat dir args
univ_tvs ex_tvs theta pat_ty
; let binds = matcher_bind `unionBags` maybe emptyBag snd m_wrapper
; traceTc "tcPatSynDecl }" $ ppr name
; let patSyn = mkPatSyn name is_infix
(map varType args)
univ_tvs ex_tvs
prov_theta req_theta
pat_ty
matcher_id (fmap fst m_wrapper)
; return (patSyn, binds) }
\end{code}
\begin{code}
tcPatSynMatcher :: Located Name
-> LPat Id
-> [Var]
-> [TcTyVar] -> [TcTyVar]
-> TcEvBinds
-> [EvVar] -> [EvVar]
-> ThetaType -> ThetaType
-> TcType
-> TcM (Id, LHsBinds Id)
tcPatSynMatcher (L loc name) lpat args univ_tvs ex_tvs ev_binds prov_dicts req_dicts prov_theta req_theta pat_ty
= do { res_tv <- zonkQuantifiedTyVar =<< newFlexiTyVar liftedTypeKind
; matcher_name <- newImplicitBinder name mkMatcherOcc
; let res_ty = TyVarTy res_tv
cont_ty = mkSigmaTy ex_tvs prov_theta $
mkFunTys (map varType args) res_ty
; let matcher_tau = mkFunTys [pat_ty, cont_ty, res_ty] res_ty
matcher_sigma = mkSigmaTy (res_tv:univ_tvs) req_theta matcher_tau
matcher_id = mkExportedLocalId VanillaId matcher_name matcher_sigma
; traceTc "tcPatSynMatcher" (ppr name $$ ppr (idType matcher_id))
; let matcher_lid = L loc matcher_id
; scrutinee <- mkId "scrut" pat_ty
; cont <- mkId "cont" cont_ty
; let cont' = nlHsApps cont $ map nlHsVar (ex_tvs ++ prov_dicts ++ args)
; fail <- mkId "fail" res_ty
; let fail' = nlHsVar fail
; let args = map nlVarPat [scrutinee, cont, fail]
lwpat = noLoc $ WildPat pat_ty
cases = if isIrrefutableHsPat lpat
then [mkSimpleHsAlt lpat cont']
else [mkSimpleHsAlt lpat cont',
mkSimpleHsAlt lwpat fail']
body = mkLHsWrap (mkWpLet ev_binds) $
L (getLoc lpat) $
HsCase (nlHsVar scrutinee) $
MG{ mg_alts = cases
, mg_arg_tys = [pat_ty]
, mg_res_ty = res_ty
, mg_origin = Generated
}
body' = noLoc $
HsLam $
MG{ mg_alts = [mkSimpleMatch args body]
, mg_arg_tys = [pat_ty, cont_ty, res_ty]
, mg_res_ty = res_ty
, mg_origin = Generated
}
match = mkMatch [] (mkHsLams (res_tv:univ_tvs) req_dicts body') EmptyLocalBinds
mg = MG{ mg_alts = [match]
, mg_arg_tys = []
, mg_res_ty = res_ty
, mg_origin = Generated
}
; let bind = FunBind{ fun_id = matcher_lid
, fun_infix = False
, fun_matches = mg
, fun_co_fn = idHsWrapper
, bind_fvs = emptyNameSet
, fun_tick = Nothing }
matcher_bind = unitBag (noLoc bind)
; traceTc "tcPatSynMatcher" (ppr matcher_bind)
; return (matcher_id, matcher_bind) }
where
mkId s ty = do
name <- newName . mkVarOccFS . fsLit $ s
return $ mkLocalId name ty
tcPatSynWrapper :: Located Name
-> LPat Name
-> HsPatSynDir Name
-> [Var]
-> [TyVar] -> [TyVar]
-> ThetaType
-> TcType
-> TcM (Maybe (Id, LHsBinds Id))
tcPatSynWrapper lname lpat dir args univ_tvs ex_tvs theta pat_ty
= do { let argNames = mkNameSet (map Var.varName args)
; case (dir, tcPatToExpr argNames lpat) of
(Unidirectional, _) ->
return Nothing
(ImplicitBidirectional, Nothing) ->
cannotInvertPatSynErr lpat
(ImplicitBidirectional, Just lexpr) ->
fmap Just $ tc_pat_syn_wrapper_from_expr lname lexpr args univ_tvs ex_tvs theta pat_ty }
tc_pat_syn_wrapper_from_expr :: Located Name
-> LHsExpr Name
-> [Var]
-> [TyVar] -> [TyVar]
-> ThetaType
-> Type
-> TcM (Id, LHsBinds Id)
tc_pat_syn_wrapper_from_expr (L loc name) lexpr args univ_tvs ex_tvs theta pat_ty
= do { let qtvs = univ_tvs ++ ex_tvs
; (subst, wrapper_tvs) <- tcInstSkolTyVars qtvs
; let wrapper_theta = substTheta subst theta
pat_ty' = substTy subst pat_ty
args' = map (\arg -> setVarType arg $ substTy subst (varType arg)) args
wrapper_tau = mkFunTys (map varType args') pat_ty'
wrapper_sigma = mkSigmaTy wrapper_tvs wrapper_theta wrapper_tau
; wrapper_name <- newImplicitBinder name mkDataConWrapperOcc
; let wrapper_lname = L loc wrapper_name
wrapper_id = mkExportedLocalId VanillaId wrapper_name wrapper_sigma
; let wrapper_args = map (noLoc . VarPat . Var.varName) args'
wrapper_match = mkMatch wrapper_args lexpr EmptyLocalBinds
bind = mkTopFunBind Generated wrapper_lname [wrapper_match]
lbind = noLoc bind
; let sig = TcSigInfo{ sig_id = wrapper_id
, sig_tvs = map (\tv -> (Nothing, tv)) wrapper_tvs
, sig_theta = wrapper_theta
, sig_tau = wrapper_tau
, sig_loc = loc
}
; (wrapper_binds, _, _) <- tcPolyCheck NonRecursive (const []) sig lbind
; traceTc "tcPatSynDecl wrapper" $ ppr wrapper_binds
; traceTc "tcPatSynDecl wrapper type" $ ppr (varType wrapper_id)
; return (wrapper_id, wrapper_binds) }
\end{code}
Note [As-patterns in pattern synonym definitions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The rationale for rejecting as-patterns in pattern synonym definitions
is that an as-pattern would introduce nonindependent pattern synonym
arguments, e.g. given a pattern synonym like:
pattern K x y = x@(Just y)
one could write a nonsensical function like
f (K Nothing x) = ...
or
g (K (Just True) False) = ...
\begin{code}
tcCheckPatSynPat :: LPat Name -> TcM ()
tcCheckPatSynPat = go
where
go :: LPat Name -> TcM ()
go = addLocM go1
go1 :: Pat Name -> TcM ()
go1 (ConPatIn _ info) = mapM_ go (hsConPatArgs info)
go1 VarPat{} = return ()
go1 WildPat{} = return ()
go1 p@(AsPat _ _) = asPatInPatSynErr p
go1 (LazyPat pat) = go pat
go1 (ParPat pat) = go pat
go1 (BangPat pat) = go pat
go1 (PArrPat pats _) = mapM_ go pats
go1 (ListPat pats _ _) = mapM_ go pats
go1 (TuplePat pats _ _) = mapM_ go pats
go1 LitPat{} = return ()
go1 NPat{} = return ()
go1 (SigPatIn pat _) = go pat
go1 (ViewPat _ pat _) = go pat
go1 p@SplicePat{} = thInPatSynErr p
go1 p@QuasiQuotePat{} = thInPatSynErr p
go1 p@NPlusKPat{} = nPlusKPatInPatSynErr p
go1 ConPatOut{} = panic "ConPatOut in output of renamer"
go1 SigPatOut{} = panic "SigPatOut in output of renamer"
go1 CoPat{} = panic "CoPat in output of renamer"
asPatInPatSynErr :: OutputableBndr name => Pat name -> TcM a
asPatInPatSynErr pat
= failWithTc $
hang (ptext (sLit "Pattern synonym definition cannot contain as-patterns (@):"))
2 (ppr pat)
thInPatSynErr :: OutputableBndr name => Pat name -> TcM a
thInPatSynErr pat
= failWithTc $
hang (ptext (sLit "Pattern synonym definition cannot contain Template Haskell:"))
2 (ppr pat)
nPlusKPatInPatSynErr :: OutputableBndr name => Pat name -> TcM a
nPlusKPatInPatSynErr pat
= failWithTc $
hang (ptext (sLit "Pattern synonym definition cannot contain n+k-pattern:"))
2 (ppr pat)
tcPatToExpr :: NameSet -> LPat Name -> Maybe (LHsExpr Name)
tcPatToExpr lhsVars = go
where
go :: LPat Name -> Maybe (LHsExpr Name)
go (L loc (ConPatIn conName info))
= do
{ let con = L loc (HsVar (unLoc conName))
; exprs <- mapM go (hsConPatArgs info)
; return $ foldl (\x y -> L loc (HsApp x y)) con exprs }
go (L loc p) = fmap (L loc) $ go1 p
go1 :: Pat Name -> Maybe (HsExpr Name)
go1 (VarPat var)
| var `elemNameSet` lhsVars = return $ HsVar var
| otherwise = Nothing
go1 (LazyPat pat) = fmap HsPar $ go pat
go1 (ParPat pat) = fmap HsPar $ go pat
go1 (BangPat pat) = fmap HsPar $ go pat
go1 (PArrPat pats ptt)
= do { exprs <- mapM go pats
; return $ ExplicitPArr ptt exprs }
go1 (ListPat pats ptt reb)
= do { exprs <- mapM go pats
; return $ ExplicitList ptt (fmap snd reb) exprs }
go1 (TuplePat pats box _)
= do { exprs <- mapM go pats
; return (ExplicitTuple (map Present exprs) box)
}
go1 (LitPat lit) = return $ HsLit lit
go1 (NPat n Nothing _) = return $ HsOverLit n
go1 (NPat n (Just neg) _) = return $ noLoc neg `HsApp` noLoc (HsOverLit n)
go1 (SigPatIn pat (HsWB ty _ _))
= do { expr <- go pat
; return $ ExprWithTySig expr ty }
go1 (ConPatOut{}) = panic "ConPatOut in output of renamer"
go1 (SigPatOut{}) = panic "SigPatOut in output of renamer"
go1 (CoPat{}) = panic "CoPat in output of renamer"
go1 _ = Nothing
cannotInvertPatSynErr :: OutputableBndr name => LPat name -> TcM a
cannotInvertPatSynErr (L loc pat)
= setSrcSpan loc $ failWithTc $
hang (ptext (sLit "Right-hand side of bidirectional pattern synonym cannot be used as an expression"))
2 (ppr pat)
tcCollectEx :: LPat Id -> TcM (TyVarSet, [EvVar])
tcCollectEx = return . go
where
go :: LPat Id -> (TyVarSet, [EvVar])
go = go1 . unLoc
go1 :: Pat Id -> (TyVarSet, [EvVar])
go1 (LazyPat p) = go p
go1 (AsPat _ p) = go p
go1 (ParPat p) = go p
go1 (BangPat p) = go p
go1 (ListPat ps _ _) = mconcat . map go $ ps
go1 (TuplePat ps _ _) = mconcat . map go $ ps
go1 (PArrPat ps _) = mconcat . map go $ ps
go1 (ViewPat _ p _) = go p
go1 (QuasiQuotePat qq) = pprPanic "TODO: tcInstPatSyn QuasiQuotePat" $ ppr qq
go1 con@ConPatOut{} = mappend (mkVarSet (pat_tvs con), pat_dicts con) $
goConDetails $ pat_args con
go1 (SigPatOut p _) = go p
go1 (CoPat _ p _) = go1 p
go1 (NPlusKPat n k geq subtract)
= pprPanic "TODO: NPlusKPat" $ ppr n $$ ppr k $$ ppr geq $$ ppr subtract
go1 _ = mempty
goConDetails :: HsConPatDetails Id -> (TyVarSet, [EvVar])
goConDetails (PrefixCon ps) = mconcat . map go $ ps
goConDetails (InfixCon p1 p2) = go p1 `mappend` go p2
goConDetails (RecCon HsRecFields{ rec_flds = flds })
= mconcat . map goRecFd $ flds
goRecFd :: HsRecField Id (LPat Id) -> (TyVarSet, [EvVar])
goRecFd HsRecField{ hsRecFieldArg = p } = go p
\end{code}