TcPat: Typechecking patterns
\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/Commentary/CodingStyle#Warnings
--- for details
-
-module TcPat ( tcLetPat, tcLamPat, tcLamPats, tcOverloadedLit,
- addDataConStupidTheta, badFieldCon, polyPatSig ) where
+module TcPat ( tcLetPat, TcSigFun, TcSigInfo(..), TcPragFun
+ , LetBndrSpec(..), addInlinePrags, warnPrags
+ , tcPat, tcPats, newNoSigLetBndr, newSigLetBndr
+ , addDataConStupidTheta, badFieldCon, polyPatSig ) where
#include "HsVersions.h"
-import {-# SOURCE #-} TcExpr( tcSyntaxOp )
+import {-# SOURCE #-} TcExpr( tcSyntaxOp, tcInferRho)
import HsSyn
import TcHsSyn
import Inst
import Id
import Var
-import CoreFVs
import Name
-import TcSimplify
import TcEnv
import TcMType
import TcType
-import VarSet
import TcUnify
import TcHsType
import TysWiredIn
-import TcGadt
-import Type
import Coercion
import StaticFlags
import TyCon
import DataCon
-import DynFlags
import PrelNames
import BasicTypes hiding (SuccessFlag(..))
+import DynFlags
import SrcLoc
-import ErrUtils
import Util
-import Maybes
import Outputable
import FastString
+import Control.Monad
\end{code}
%************************************************************************
\begin{code}
-tcLetPat :: (Name -> Maybe TcRhoType)
- -> LPat Name -> BoxySigmaType
- -> TcM a
+tcLetPat :: TcSigFun -> LetBndrSpec
+ -> LPat Name -> TcSigmaType
+ -> TcM a
-> TcM (LPat TcId, a)
-tcLetPat sig_fn pat pat_ty thing_inside
- = do { let init_state = PS { pat_ctxt = LetPat sig_fn,
- pat_reft = emptyRefinement,
- pat_eqs = False }
- ; (pat', ex_tvs, res) <- tc_lpat pat pat_ty init_state (\ _ -> thing_inside)
-
- -- Don't know how to deal with pattern-bound existentials yet
- ; checkTc (null ex_tvs) (existentialExplode pat)
-
- ; return (pat', res) }
+tcLetPat sig_fn no_gen pat pat_ty thing_inside
+ = tc_lpat pat pat_ty penv thing_inside
+ where
+ penv = PE { pe_lazy = True
+ , pe_ctxt = LetPat sig_fn no_gen }
-----------------
-tcLamPats :: [LPat Name] -- Patterns,
- -> [BoxySigmaType] -- and their types
- -> BoxyRhoType -- Result type,
- -> ((Refinement, BoxyRhoType) -> TcM a) -- and the checker for the body
- -> TcM ([LPat TcId], a)
+tcPats :: HsMatchContext Name
+ -> [LPat Name] -- Patterns,
+ -> [TcSigmaType] -- and their types
+ -> TcM a -- and the checker for the body
+ -> TcM ([LPat TcId], a)
-- This is the externally-callable wrapper function
-- Typecheck the patterns, extend the environment to bind the variables,
-- 1. Initialise the PatState
-- 2. Check the patterns
--- 3. Apply the refinement to the environment and result type
--- 4. Check the body
--- 5. Check that no existentials escape
-
-tcLamPats pats tys res_ty thing_inside
- = tc_lam_pats (zipEqual "tcLamPats" pats tys)
- (emptyRefinement, res_ty) thing_inside
+-- 3. Check the body
+-- 4. Check that no existentials escape
-tcLamPat :: LPat Name -> BoxySigmaType
- -> (Refinement,BoxyRhoType) -- Result type
- -> ((Refinement,BoxyRhoType) -> TcM a) -- Checker for body, given its result type
- -> TcM (LPat TcId, a)
-tcLamPat pat pat_ty res_ty thing_inside
- = do { ([pat'],thing) <- tc_lam_pats [(pat, pat_ty)] res_ty thing_inside
- ; return (pat', thing) }
+tcPats ctxt pats pat_tys thing_inside
+ = tc_lpats penv pats pat_tys thing_inside
+ where
+ penv = PE { pe_lazy = False, pe_ctxt = LamPat ctxt }
+
+tcPat :: HsMatchContext Name
+ -> LPat Name -> TcSigmaType
+ -> TcM a -- Checker for body, given
+ -- its result type
+ -> TcM (LPat TcId, a)
+tcPat ctxt pat pat_ty thing_inside
+ = tc_lpat pat pat_ty penv thing_inside
+ where
+ penv = PE { pe_lazy = False, pe_ctxt = LamPat ctxt }
+
-----------------
-tc_lam_pats :: [(LPat Name,BoxySigmaType)]
- -> (Refinement,BoxyRhoType) -- Result type
- -> ((Refinement,BoxyRhoType) -> TcM a) -- Checker for body, given its result type
- -> TcM ([LPat TcId], a)
-tc_lam_pats pat_ty_prs (reft, res_ty) thing_inside
- = do { let init_state = PS { pat_ctxt = LamPat, pat_reft = reft, pat_eqs = False }
+data PatEnv
+ = PE { pe_lazy :: Bool -- True <=> lazy context, so no existentials allowed
+ , pe_ctxt :: PatCtxt -- Context in which the whole pattern appears
+ }
- ; (pats', ex_tvs, res) <- tcMultiple tc_lpat_pr pat_ty_prs init_state $ \ pstate' ->
- refineEnvironment (pat_reft pstate') (pat_eqs pstate') $
- if (pat_eqs pstate' && (not $ isRigidTy res_ty))
- then failWithTc (nonRigidResult res_ty)
- else thing_inside (pat_reft pstate', res_ty)
+data PatCtxt
+ = LamPat -- Used for lambdas, case etc
+ (HsMatchContext Name)
- ; let tys = map snd pat_ty_prs
- ; tcCheckExistentialPat pats' ex_tvs tys res_ty
+ | LetPat -- Used only for let(rec) bindings
+ -- See Note [Let binders]
+ TcSigFun -- Tells type sig if any
+ LetBndrSpec -- True <=> no generalisation of this let
- ; returnM (pats', res) }
+data LetBndrSpec
+ = LetLclBndr -- The binder is just a local one;
+ -- an AbsBinds will provide the global version
+ | LetGblBndr TcPragFun -- There isn't going to be an AbsBinds;
+ -- here is the inline-pragma information
------------------
-tcCheckExistentialPat :: [LPat TcId] -- Patterns (just for error message)
- -> [TcTyVar] -- Existentially quantified tyvars bound by pattern
- -> [BoxySigmaType] -- Types of the patterns
- -> BoxyRhoType -- Type of the body of the match
- -- Tyvars in either of these must not escape
- -> TcM ()
--- NB: we *must* pass "pats_tys" not just "body_ty" to tcCheckExistentialPat
--- For example, we must reject this program:
--- data C = forall a. C (a -> Int)
--- f (C g) x = g x
--- Here, result_ty will be simply Int, but expected_ty is (C -> a -> Int).
-
-tcCheckExistentialPat pats [] pat_tys body_ty
- = return () -- Short cut for case when there are no existentials
-
-tcCheckExistentialPat pats ex_tvs pat_tys body_ty
- = addErrCtxtM (sigPatCtxt pats ex_tvs pat_tys body_ty) $
- checkSigTyVarsWrt (tcTyVarsOfTypes (body_ty:pat_tys)) ex_tvs
-
-data PatState = PS {
- pat_ctxt :: PatCtxt,
- pat_reft :: Refinement, -- Binds rigid TcTyVars to their refinements
- pat_eqs :: Bool -- <=> there are GADT equational constraints
- -- for refinement
- }
-
-data PatCtxt
- = LamPat
- | LetPat (Name -> Maybe TcRhoType) -- Used for let(rec) bindings
-
-patSigCtxt :: PatState -> UserTypeCtxt
-patSigCtxt (PS { pat_ctxt = LetPat _ }) = BindPatSigCtxt
-patSigCtxt other = LamPatSigCtxt
+makeLazy :: PatEnv -> PatEnv
+makeLazy penv = penv { pe_lazy = True }
+
+patSigCtxt :: PatEnv -> UserTypeCtxt
+patSigCtxt (PE { pe_ctxt = LetPat {} }) = BindPatSigCtxt
+patSigCtxt (PE { pe_ctxt = LamPat {} }) = LamPatSigCtxt
+
+---------------
+type TcPragFun = Name -> [LSig Name]
+type TcSigFun = Name -> Maybe TcSigInfo
+
+data TcSigInfo
+ = TcSigInfo {
+ sig_id :: TcId, -- *Polymorphic* binder for this value...
+
+ sig_scoped :: [Name], -- Scoped type variables
+ -- 1-1 correspondence with a prefix of sig_tvs
+ -- However, may be fewer than sig_tvs;
+ -- see Note [More instantiated than scoped]
+ sig_tvs :: [TcTyVar], -- Instantiated type variables
+ -- See Note [Instantiate sig]
+
+ sig_theta :: TcThetaType, -- Instantiated theta
+
+ sig_tau :: TcSigmaType, -- Instantiated tau
+ -- See Note [sig_tau may be polymorphic]
+
+ sig_loc :: SrcSpan -- The location of the signature
+ }
+
+instance Outputable TcSigInfo where
+ ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
+ = ppr id <+> ptext (sLit "::") <+> ppr tyvars <+> pprThetaArrowTy theta <+> ppr tau
\end{code}
+Note [sig_tau may be polymorphic]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Note that "sig_tau" might actually be a polymorphic type,
+if the original function had a signature like
+ forall a. Eq a => forall b. Ord b => ....
+But that's ok: tcMatchesFun (called by tcRhs) can deal with that
+It happens, too! See Note [Polymorphic methods] in TcClassDcl.
+
+Note [Let binders]
+~~~~~~~~~~~~~~~~~~
+eg x :: Int
+ y :: Bool
+ (x,y) = e
+
+...more notes to add here..
+
+
+Note [Existential check]
+~~~~~~~~~~~~~~~~~~~~~~~~
+Lazy patterns can't bind existentials. They arise in two ways:
+ * Let bindings let { C a b = e } in b
+ * Twiddle patterns f ~(C a b) = e
+The pe_lazy field of PatEnv says whether we are inside a lazy
+pattern (perhaps deeply)
+
+If we aren't inside a lazy pattern then we can bind existentials,
+but we need to be careful about "extra" tyvars. Consider
+ (\C x -> d) : pat_ty -> res_ty
+When looking for existential escape we must check that the existential
+bound by C don't unify with the free variables of pat_ty, OR res_ty
+(or of course the environment). Hence we need to keep track of the
+res_ty free vars.
%************************************************************************
%************************************************************************
\begin{code}
-tcPatBndr :: PatState -> Name -> BoxySigmaType -> TcM TcId
-tcPatBndr (PS { pat_ctxt = LamPat }) bndr_name pat_ty
- = do { pat_ty' <- unBoxPatBndrType pat_ty bndr_name
- -- We have an undecorated binder, so we do rule ABS1,
- -- by unboxing the boxy type, forcing any un-filled-in
- -- boxes to become monotypes
- -- NB that pat_ty' can still be a polytype:
- -- data T = MkT (forall a. a->a)
- -- f t = case t of { MkT g -> ... }
- -- Here, the 'g' must get type (forall a. a->a) from the
- -- MkT context
- ; return (Id.mkLocalId bndr_name pat_ty') }
-
-tcPatBndr (PS { pat_ctxt = LetPat lookup_sig }) bndr_name pat_ty
- | Just mono_ty <- lookup_sig bndr_name
- = do { mono_name <- newLocalName bndr_name
- ; boxyUnify mono_ty pat_ty
- ; return (Id.mkLocalId mono_name mono_ty) }
-
+tcPatBndr :: PatEnv -> Name -> TcSigmaType -> TcM (Coercion, TcId)
+-- (coi, xp) = tcPatBndr penv x pat_ty
+-- Then coi : pat_ty ~ typeof(xp)
+--
+tcPatBndr (PE { pe_ctxt = LetPat lookup_sig no_gen}) bndr_name pat_ty
+ | Just sig <- lookup_sig bndr_name
+ = do { bndr_id <- newSigLetBndr no_gen bndr_name sig
+ ; coi <- unifyPatType (idType bndr_id) pat_ty
+ ; return (coi, bndr_id) }
+
| otherwise
- = do { pat_ty' <- unBoxPatBndrType pat_ty bndr_name
- ; mono_name <- newLocalName bndr_name
- ; return (Id.mkLocalId mono_name pat_ty') }
+ = do { bndr_id <- newNoSigLetBndr no_gen bndr_name pat_ty
+ ; return (mkReflCo pat_ty, bndr_id) }
+
+tcPatBndr (PE { pe_ctxt = _lam_or_proc }) bndr_name pat_ty
+ = do { bndr <- mkLocalBinder bndr_name pat_ty
+ ; return (mkReflCo pat_ty, bndr) }
+
+------------
+newSigLetBndr :: LetBndrSpec -> Name -> TcSigInfo -> TcM TcId
+newSigLetBndr LetLclBndr name sig
+ = do { mono_name <- newLocalName name
+ ; mkLocalBinder mono_name (sig_tau sig) }
+newSigLetBndr (LetGblBndr prags) name sig
+ = addInlinePrags (sig_id sig) (prags name)
+
+------------
+newNoSigLetBndr :: LetBndrSpec -> Name -> TcType -> TcM TcId
+-- In the polymorphic case (no_gen = False), generate a "monomorphic version"
+-- of the Id; the original name will be bound to the polymorphic version
+-- by the AbsBinds
+-- In the monomorphic case there is no AbsBinds, and we use the original
+-- name directly
+newNoSigLetBndr LetLclBndr name ty
+ =do { mono_name <- newLocalName name
+ ; mkLocalBinder mono_name ty }
+newNoSigLetBndr (LetGblBndr prags) name ty
+ = do { id <- mkLocalBinder name ty
+ ; addInlinePrags id (prags name) }
+
+----------
+addInlinePrags :: TcId -> [LSig Name] -> TcM TcId
+addInlinePrags poly_id prags
+ = tc_inl inl_sigs
+ where
+ inl_sigs = filter isInlineLSig prags
+ tc_inl [] = return poly_id
+ tc_inl (L loc (InlineSig _ prag) : other_inls)
+ = do { unless (null other_inls) (setSrcSpan loc warn_dup_inline)
+ ; return (poly_id `setInlinePragma` prag) }
+ tc_inl _ = panic "tc_inl"
+
+ warn_dup_inline = warnPrags poly_id inl_sigs $
+ ptext (sLit "Duplicate INLINE pragmas for")
+
+warnPrags :: Id -> [LSig Name] -> SDoc -> TcM ()
+warnPrags id bad_sigs herald
+ = addWarnTc (hang (herald <+> quotes (ppr id))
+ 2 (ppr_sigs bad_sigs))
+ where
+ ppr_sigs sigs = vcat (map (ppr . getLoc) sigs)
+-----------------
+mkLocalBinder :: Name -> TcType -> TcM TcId
+mkLocalBinder name ty
+ = do { checkUnboxedTuple ty $
+ ptext (sLit "The variable") <+> quotes (ppr name)
+ ; return (Id.mkLocalId name ty) }
+
+checkUnboxedTuple :: TcType -> SDoc -> TcM ()
+-- Check for an unboxed tuple type
+-- f = (# True, False #)
+-- Zonk first just in case it's hidden inside a meta type variable
+-- (This shows up as a (more obscure) kind error
+-- in the 'otherwise' case of tcMonoBinds.)
+checkUnboxedTuple ty what
+ = do { zonked_ty <- zonkTcTypeCarefully ty
+ ; checkTc (not (isUnboxedTupleType zonked_ty))
+ (unboxedTupleErr what zonked_ty) }
-------------------
-bindInstsOfPatId :: TcId -> TcM a -> TcM (a, LHsBinds TcId)
+{- Only needed if we re-add Method constraints
+bindInstsOfPatId :: TcId -> TcM a -> TcM (a, TcEvBinds)
bindInstsOfPatId id thing_inside
| not (isOverloadedTy (idType id))
- = do { res <- thing_inside; return (res, emptyLHsBinds) }
+ = do { res <- thing_inside; return (res, emptyTcEvBinds) }
| otherwise
- = do { (res, lie) <- getLIE thing_inside
- ; binds <- bindInstsOfLocalFuns lie [id]
+ = do { (res, lie) <- captureConstraints thing_inside
+ ; binds <- bindLocalMethods lie [id]
; return (res, binds) }
-
--------------------
-unBoxPatBndrType ty name = unBoxArgType ty (ptext SLIT("The variable") <+> quotes (ppr name))
-unBoxWildCardType ty = unBoxArgType ty (ptext SLIT("A wild-card pattern"))
-
-unBoxArgType :: BoxyType -> SDoc -> TcM TcType
--- In addition to calling unbox, unBoxArgType ensures that the type is of ArgTypeKind;
--- that is, it can't be an unboxed tuple. For example,
--- case (f x) of r -> ...
--- should fail if 'f' returns an unboxed tuple.
-unBoxArgType ty pp_this
- = do { ty' <- unBox ty -- Returns a zonked type
-
- -- Neither conditional is strictly necesssary (the unify alone will do)
- -- but they improve error messages, and allocate fewer tyvars
- ; if isUnboxedTupleType ty' then
- failWithTc msg
- else if isSubArgTypeKind (typeKind ty') then
- return ty'
- else do -- OpenTypeKind, so constrain it
- { ty2 <- newFlexiTyVarTy argTypeKind
- ; unifyType ty' ty2
- ; return ty' }}
- where
- msg = pp_this <+> ptext SLIT("cannot be bound to an unboxed tuple")
+-}
\end{code}
+Note [Polymorphism and pattern bindings]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When is_mono holds we are not generalising
+But the signature can still be polymoprhic!
+ data T = MkT (forall a. a->a)
+ x :: forall a. a->a
+ MkT x = <rhs>
+So the no_gen flag decides whether the pattern-bound variables should
+have exactly the type in the type signature (when not generalising) or
+the instantiated version (when generalising)
%************************************************************************
%* *
This does not work so well for the ErrCtxt carried by the monad: we don't
want the error-context for the pattern to scope over the RHS.
-Hence the getErrCtxt/setErrCtxt stuff in tc_lpats.
+Hence the getErrCtxt/setErrCtxt stuff in tcMultiple
\begin{code}
--------------------
type Checker inp out = forall r.
inp
- -> PatState
- -> (PatState -> TcM r)
- -> TcM (out, [TcTyVar], r)
+ -> PatEnv
+ -> TcM r
+ -> TcM (out, r)
tcMultiple :: Checker inp out -> Checker [inp] [out]
-tcMultiple tc_pat args pstate thing_inside
+tcMultiple tc_pat args penv thing_inside
= do { err_ctxt <- getErrCtxt
- ; let loop pstate []
- = do { res <- thing_inside pstate
- ; return ([], [], res) }
+ ; let loop _ []
+ = do { res <- thing_inside
+ ; return ([], res) }
- loop pstate (arg:args)
- = do { (p', p_tvs, (ps', ps_tvs, res))
- <- tc_pat arg pstate $ \ pstate' ->
+ loop penv (arg:args)
+ = do { (p', (ps', res))
+ <- tc_pat arg penv $
setErrCtxt err_ctxt $
- loop pstate' args
+ loop penv args
-- setErrCtxt: restore context before doing the next pattern
-- See note [Nesting] above
- ; return (p':ps', p_tvs ++ ps_tvs, res) }
+ ; return (p':ps', res) }
- ; loop pstate args }
+ ; loop penv args }
--------------------
-tc_lpat_pr :: (LPat Name, BoxySigmaType)
- -> PatState
- -> (PatState -> TcM a)
- -> TcM (LPat TcId, [TcTyVar], a)
-tc_lpat_pr (pat, ty) = tc_lpat pat ty
-
tc_lpat :: LPat Name
- -> BoxySigmaType
- -> PatState
- -> (PatState -> TcM a)
- -> TcM (LPat TcId, [TcTyVar], a)
-tc_lpat (L span pat) pat_ty pstate thing_inside
- = setSrcSpan span $
- maybeAddErrCtxt (patCtxt pat) $
- do { let mb_reft = refineType (pat_reft pstate) pat_ty
- pat_ty' = case mb_reft of { Just (_, ty') -> ty'; Nothing -> pat_ty }
-
- -- Make sure the result type reflects the current refinement
- -- We must do this here, so that it correctly ``sees'' all
- -- the refinements to the left. Example:
- -- Suppose C :: forall a. T a -> a -> Foo
- -- Pattern C a p1 True
- -- So p1 might refine 'a' to True, and the True
- -- pattern had better see it.
-
- ; (pat', tvs, res) <- tc_pat pstate pat pat_ty' thing_inside
- ; let final_pat = case mb_reft of
- Nothing -> pat'
- Just (co,_) -> CoPat (WpCo co) pat' pat_ty
- ; return (L span final_pat, tvs, res) }
+ -> TcSigmaType
+ -> PatEnv
+ -> TcM a
+ -> TcM (LPat TcId, a)
+tc_lpat (L span pat) pat_ty penv thing_inside
+ = setSrcSpan span $
+ do { (pat', res) <- maybeWrapPatCtxt pat (tc_pat penv pat pat_ty)
+ thing_inside
+ ; return (L span pat', res) }
+
+tc_lpats :: PatEnv
+ -> [LPat Name] -> [TcSigmaType]
+ -> TcM a
+ -> TcM ([LPat TcId], a)
+tc_lpats penv pats tys thing_inside
+ = tcMultiple (\(p,t) -> tc_lpat p t)
+ (zipEqual "tc_lpats" pats tys)
+ penv thing_inside
--------------------
-tc_pat :: PatState
- -> Pat Name -> BoxySigmaType -- Fully refined result type
- -> (PatState -> TcM a) -- Thing inside
- -> TcM (Pat TcId, -- Translated pattern
- [TcTyVar], -- Existential binders
- a) -- Result of thing inside
-
-tc_pat pstate (VarPat name) pat_ty thing_inside
- = do { id <- tcPatBndr pstate name pat_ty
- ; (res, binds) <- bindInstsOfPatId id $
- tcExtendIdEnv1 name id $
- (traceTc (text "binding" <+> ppr name <+> ppr (idType id))
- >> thing_inside pstate)
- ; let pat' | isEmptyLHsBinds binds = VarPat id
- | otherwise = VarPatOut id binds
- ; return (pat', [], res) }
-
-tc_pat pstate (ParPat pat) pat_ty thing_inside
- = do { (pat', tvs, res) <- tc_lpat pat pat_ty pstate thing_inside
- ; return (ParPat pat', tvs, res) }
-
-tc_pat pstate (BangPat pat) pat_ty thing_inside
- = do { (pat', tvs, res) <- tc_lpat pat pat_ty pstate thing_inside
- ; return (BangPat pat', tvs, res) }
-
--- There's a wrinkle with irrefutable patterns, namely that we
--- must not propagate type refinement from them. For example
--- data T a where { T1 :: Int -> T Int; ... }
--- f :: T a -> Int -> a
--- f ~(T1 i) y = y
--- It's obviously not sound to refine a to Int in the right
--- hand side, because the arugment might not match T1 at all!
---
--- Nor should a lazy pattern bind any existential type variables
--- because they won't be in scope when we do the desugaring
---
--- Note [Hopping the LIE in lazy patterns]
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--- In a lazy pattern, we must *not* discharge constraints from the RHS
--- from dictionaries bound in the pattern. E.g.
--- f ~(C x) = 3
--- We can't discharge the Num constraint from dictionaries bound by
--- the pattern C!
---
--- So we have to make the constraints from thing_inside "hop around"
--- the pattern. Hence the getLLE and extendLIEs later.
-
-tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
- = do { (pat', pat_tvs, (res,lie))
- <- tc_lpat pat pat_ty pstate $ \ _ ->
- getLIE (thing_inside pstate)
- -- Ignore refined pstate', revert to pstate
- ; extendLIEs lie
- -- getLIE/extendLIEs: see Note [Hopping the LIE in lazy patterns]
-
- -- Check no existentials
- ; if (null pat_tvs) then return ()
- else lazyPatErr lpat pat_tvs
-
- -- Check that the pattern has a lifted type
- ; pat_tv <- newBoxyTyVar liftedTypeKind
- ; boxyUnify pat_ty (mkTyVarTy pat_tv)
-
- ; return (LazyPat pat', [], res) }
-
-tc_pat pstate (WildPat _) pat_ty thing_inside
- = do { pat_ty' <- unBoxWildCardType pat_ty -- Make sure it's filled in with monotypes
- ; res <- thing_inside pstate
- ; return (WildPat pat_ty', [], res) }
-
-tc_pat pstate (AsPat (L nm_loc name) pat) pat_ty thing_inside
- = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
- ; (pat', tvs, res) <- tcExtendIdEnv1 name bndr_id $
- tc_lpat pat (idType bndr_id) pstate thing_inside
+tc_pat :: PatEnv
+ -> Pat Name
+ -> TcSigmaType -- Fully refined result type
+ -> TcM a -- Thing inside
+ -> TcM (Pat TcId, -- Translated pattern
+ a) -- Result of thing inside
+
+tc_pat penv (VarPat name) pat_ty thing_inside
+ = do { (coi, id) <- tcPatBndr penv name pat_ty
+ ; res <- tcExtendIdEnv1 name id thing_inside
+ ; return (mkHsWrapPatCo coi (VarPat id) pat_ty, res) }
+
+tc_pat penv (ParPat pat) pat_ty thing_inside
+ = do { (pat', res) <- tc_lpat pat pat_ty penv thing_inside
+ ; return (ParPat pat', res) }
+
+tc_pat penv (BangPat pat) pat_ty thing_inside
+ = do { (pat', res) <- tc_lpat pat pat_ty penv thing_inside
+ ; return (BangPat pat', res) }
+
+tc_pat penv lpat@(LazyPat pat) pat_ty thing_inside
+ = do { (pat', (res, pat_ct))
+ <- tc_lpat pat pat_ty (makeLazy penv) $
+ captureConstraints thing_inside
+ -- Ignore refined penv', revert to penv
+
+ ; emitConstraints pat_ct
+ -- captureConstraints/extendConstraints:
+ -- see Note [Hopping the LIE in lazy patterns]
+
+ -- Check there are no unlifted types under the lazy pattern
+ ; when (any (isUnLiftedType . idType) $ collectPatBinders pat') $
+ lazyUnliftedPatErr lpat
+
+ -- Check that the expected pattern type is itself lifted
+ ; pat_ty' <- newFlexiTyVarTy liftedTypeKind
+ ; _ <- unifyType pat_ty pat_ty'
+
+ ; return (LazyPat pat', res) }
+
+tc_pat _ p@(QuasiQuotePat _) _ _
+ = pprPanic "Should never see QuasiQuotePat in type checker" (ppr p)
+
+tc_pat _ (WildPat _) pat_ty thing_inside
+ = do { checkUnboxedTuple pat_ty $
+ ptext (sLit "A wild-card pattern")
+ ; res <- thing_inside
+ ; return (WildPat pat_ty, res) }
+
+tc_pat penv (AsPat (L nm_loc name) pat) pat_ty thing_inside
+ = do { (coi, bndr_id) <- setSrcSpan nm_loc (tcPatBndr penv name pat_ty)
+ ; (pat', res) <- tcExtendIdEnv1 name bndr_id $
+ tc_lpat pat (idType bndr_id) penv thing_inside
-- NB: if we do inference on:
-- \ (y@(x::forall a. a->a)) = e
-- we'll fail. The as-pattern infers a monotype for 'y', which then
-- perhaps be fixed, but only with a bit more work.
--
-- If you fix it, don't forget the bindInstsOfPatIds!
- ; return (AsPat (L nm_loc bndr_id) pat', tvs, res) }
+ ; return (mkHsWrapPatCo coi (AsPat (L nm_loc bndr_id) pat') pat_ty, res) }
+
+tc_pat penv vpat@(ViewPat expr pat _) overall_pat_ty thing_inside
+ = do { checkUnboxedTuple overall_pat_ty $
+ ptext (sLit "The view pattern") <+> ppr vpat
+
+ -- Morally, expr must have type `forall a1...aN. OPT' -> B`
+ -- where overall_pat_ty is an instance of OPT'.
+ -- Here, we infer a rho type for it,
+ -- which replaces the leading foralls and constraints
+ -- with fresh unification variables.
+ ; (expr',expr'_inferred) <- tcInferRho expr
+
+ -- next, we check that expr is coercible to `overall_pat_ty -> pat_ty`
+ -- NOTE: this forces pat_ty to be a monotype (because we use a unification
+ -- variable to find it). this means that in an example like
+ -- (view -> f) where view :: _ -> forall b. b
+ -- we will only be able to use view at one instantation in the
+ -- rest of the view
+ ; (expr_coi, pat_ty) <- tcInfer $ \ pat_ty ->
+ unifyPatType expr'_inferred (mkFunTy overall_pat_ty pat_ty)
+
+ -- pattern must have pat_ty
+ ; (pat', res) <- tc_lpat pat pat_ty penv thing_inside
+
+ ; return (ViewPat (mkLHsWrapCo expr_coi expr') pat' overall_pat_ty, res) }
-- Type signatures in patterns
-- See Note [Pattern coercions] below
-tc_pat pstate (SigPatIn pat sig_ty) pat_ty thing_inside
- = do { (inner_ty, tv_binds) <- tcPatSig (patSigCtxt pstate) sig_ty pat_ty
- ; (pat', tvs, res) <- tcExtendTyVarEnv2 tv_binds $
- tc_lpat pat inner_ty pstate thing_inside
- ; return (SigPatOut pat' inner_ty, tvs, res) }
+tc_pat penv (SigPatIn pat sig_ty) pat_ty thing_inside
+ = do { (inner_ty, tv_binds, wrap) <- tcPatSig (patSigCtxt penv) sig_ty pat_ty
+ ; (pat', res) <- tcExtendTyVarEnv2 tv_binds $
+ tc_lpat pat inner_ty penv thing_inside
-tc_pat pstate pat@(TypePat ty) pat_ty thing_inside
- = failWithTc (badTypePat pat)
+ ; return (mkHsWrapPat wrap (SigPatOut pat' inner_ty) pat_ty, res) }
------------------------
-- Lists, tuples, arrays
-tc_pat pstate (ListPat pats _) pat_ty thing_inside
- = do { elt_ty <- boxySplitListTy pat_ty
- ; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
- pats pstate thing_inside
- ; return (ListPat pats' elt_ty, pats_tvs, res) }
-
-tc_pat pstate (PArrPat pats _) pat_ty thing_inside
- = do { [elt_ty] <- boxySplitTyConApp parrTyCon pat_ty
- ; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
- pats pstate thing_inside
- ; ifM (null pats) (zapToMonotype pat_ty) -- c.f. ExplicitPArr in TcExpr
- ; return (PArrPat pats' elt_ty, pats_tvs, res) }
-
-tc_pat pstate (TuplePat pats boxity _) pat_ty thing_inside
- = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length pats)) pat_ty
- ; (pats', pats_tvs, res) <- tcMultiple tc_lpat_pr (pats `zip` arg_tys)
- pstate thing_inside
+tc_pat penv (ListPat pats _) pat_ty thing_inside
+ = do { (coi, elt_ty) <- matchExpectedPatTy matchExpectedListTy pat_ty
+ ; (pats', res) <- tcMultiple (\p -> tc_lpat p elt_ty)
+ pats penv thing_inside
+ ; return (mkHsWrapPat coi (ListPat pats' elt_ty) pat_ty, res)
+ }
+
+tc_pat penv (PArrPat pats _) pat_ty thing_inside
+ = do { (coi, elt_ty) <- matchExpectedPatTy matchExpectedPArrTy pat_ty
+ ; (pats', res) <- tcMultiple (\p -> tc_lpat p elt_ty)
+ pats penv thing_inside
+ ; return (mkHsWrapPat coi (PArrPat pats' elt_ty) pat_ty, res)
+ }
+
+tc_pat penv (TuplePat pats boxity _) pat_ty thing_inside
+ = do { let tc = tupleTyCon boxity (length pats)
+ ; (coi, arg_tys) <- matchExpectedPatTy (matchExpectedTyConApp tc) pat_ty
+ ; (pats', res) <- tc_lpats penv pats arg_tys thing_inside
-- Under flag control turn a pattern (x,y,z) into ~(x,y,z)
-- so that we can experiment with lazy tuple-matching.
-- This is a pretty odd place to make the switch, but
-- it was easy to do.
- ; let unmangled_result = TuplePat pats' boxity pat_ty
+ ; let pat_ty' = mkTyConApp tc arg_tys
+ -- pat_ty /= pat_ty iff coi /= IdCo
+ unmangled_result = TuplePat pats' boxity pat_ty'
possibly_mangled_result
- | opt_IrrefutableTuples && isBoxed boxity = LazyPat (noLoc unmangled_result)
- | otherwise = unmangled_result
+ | opt_IrrefutableTuples &&
+ isBoxed boxity = LazyPat (noLoc unmangled_result)
+ | otherwise = unmangled_result
- ; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
- return (possibly_mangled_result, pats_tvs, res) }
+ ; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
+ return (mkHsWrapPat coi possibly_mangled_result pat_ty, res)
+ }
------------------------
-- Data constructors
-tc_pat pstate pat_in@(ConPatIn (L con_span con_name) arg_pats) pat_ty thing_inside
- = do { data_con <- tcLookupDataCon con_name
- ; let tycon = dataConTyCon data_con
- ; tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside }
+tc_pat penv (ConPatIn con arg_pats) pat_ty thing_inside
+ = tcConPat penv con pat_ty arg_pats thing_inside
------------------------
-- Literal patterns
-tc_pat pstate (LitPat simple_lit) pat_ty thing_inside
+tc_pat _ (LitPat simple_lit) pat_ty thing_inside
= do { let lit_ty = hsLitType simple_lit
- ; coi <- boxyUnify lit_ty pat_ty
- -- coi is of kind: lit_ty ~ pat_ty
- ; res <- thing_inside pstate
- ; span <- getSrcSpanM
- -- pattern coercions have to
- -- be of kind: pat_ty ~ lit_ty
- -- hence, sym coi
- ; returnM (wrapPatCoI (mkSymCoI coi) (LitPat simple_lit) pat_ty, [], res) }
+ ; coi <- unifyPatType lit_ty pat_ty
+ -- coi is of kind: pat_ty ~ lit_ty
+ ; res <- thing_inside
+ ; return ( mkHsWrapPatCo coi (LitPat simple_lit) pat_ty
+ , res) }
------------------------
-- Overloaded patterns: n, and n+k
-tc_pat pstate pat@(NPat over_lit mb_neg eq _) pat_ty thing_inside
+tc_pat _ (NPat over_lit mb_neg eq) pat_ty thing_inside
= do { let orig = LiteralOrigin over_lit
- ; lit' <- tcOverloadedLit orig over_lit pat_ty
+ ; lit' <- newOverloadedLit orig over_lit pat_ty
; eq' <- tcSyntaxOp orig eq (mkFunTys [pat_ty, pat_ty] boolTy)
; mb_neg' <- case mb_neg of
Nothing -> return Nothing -- Positive literal
-- The 'negate' is re-mappable syntax
do { neg' <- tcSyntaxOp orig neg (mkFunTy pat_ty pat_ty)
; return (Just neg') }
- ; res <- thing_inside pstate
- ; returnM (NPat lit' mb_neg' eq' pat_ty, [], res) }
+ ; res <- thing_inside
+ ; return (NPat lit' mb_neg' eq', res) }
-tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
- = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
+tc_pat penv (NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
+ = do { (coi, bndr_id) <- setSrcSpan nm_loc (tcPatBndr penv name pat_ty)
; let pat_ty' = idType bndr_id
orig = LiteralOrigin lit
- ; lit' <- tcOverloadedLit orig lit pat_ty'
+ ; lit' <- newOverloadedLit orig lit pat_ty'
-- The '>=' and '-' parts are re-mappable syntax
; ge' <- tcSyntaxOp orig ge (mkFunTys [pat_ty', pat_ty'] boolTy)
; minus' <- tcSyntaxOp orig minus (mkFunTys [pat_ty', pat_ty'] pat_ty')
+ ; let pat' = NPlusKPat (L nm_loc bndr_id) lit' ge' minus'
-- The Report says that n+k patterns must be in Integral
-- We may not want this when using re-mappable syntax, though (ToDo?)
; icls <- tcLookupClass integralClassName
; instStupidTheta orig [mkClassPred icls [pat_ty']]
- ; res <- tcExtendIdEnv1 name bndr_id (thing_inside pstate)
- ; returnM (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
-
-tc_pat _ _other_pat _ _ = panic "tc_pat" -- ConPatOut, SigPatOut, VarPatOut
+ ; res <- tcExtendIdEnv1 name bndr_id thing_inside
+ ; return (mkHsWrapPatCo coi pat' pat_ty, res) }
+
+tc_pat _ _other_pat _ _ = panic "tc_pat" -- ConPatOut, SigPatOut
+
+----------------
+unifyPatType :: TcType -> TcType -> TcM Coercion
+-- In patterns we want a coercion from the
+-- context type (expected) to the actual pattern type
+-- But we don't want to reverse the args to unifyType because
+-- that controls the actual/expected stuff in error messages
+unifyPatType actual_ty expected_ty
+ = do { coi <- unifyType actual_ty expected_ty
+ ; return (mkSymCo coi) }
\end{code}
+Note [Hopping the LIE in lazy patterns]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+In a lazy pattern, we must *not* discharge constraints from the RHS
+from dictionaries bound in the pattern. E.g.
+ f ~(C x) = 3
+We can't discharge the Num constraint from dictionaries bound by
+the pattern C!
+
+So we have to make the constraints from thing_inside "hop around"
+the pattern. Hence the captureConstraints and emitConstraints.
+
+The same thing ensures that equality constraints in a lazy match
+are not made available in the RHS of the match. For example
+ data T a where { T1 :: Int -> T Int; ... }
+ f :: T a -> Int -> a
+ f ~(T1 i) y = y
+It's obviously not sound to refine a to Int in the right
+hand side, because the arugment might not match T1 at all!
+
+Finally, a lazy pattern should not bind any existential type variables
+because they won't be in scope when we do the desugaring
+
%************************************************************************
%* *
In other words, boxySplitTyConAppWithFamily implicitly takes the coercion
- Co123Map a b v :: {Map (a, b) v :=: :R123Map a b v}
+ Co123Map a b v :: {Map (a, b) v ~ :R123Map a b v}
moving between representation and family type into account. To produce type
correct Core, this coercion needs to be used to case the type of the scrutinee
from the family to the representation type. This is achieved by
unwrapFamInstScrutinee using a CoPat around the result pattern.
-Now it might appear seem as if we could have used the existing GADT type
+Now it might appear seem as if we could have used the previous GADT type
refinement infrastructure of refineAlt and friends instead of the explicit
unification and CoPat generation. However, that would be wrong. Why? The
whole point of GADT refinement is that the refinement is local to the case
alternatives of the case expression, whereas in the GADT case it might vary
between alternatives.
-In fact, if we have a data instance declaration defining a GADT, eq_spec will
-be non-empty and we will get a mixture of global instantiations and local
-refinement from a single match. This neatly reflects that, as soon as we
-have constrained the type of the scrutinee to the required type index, all
-further type refinement is local to the alternative.
+RIP GADT refinement: refinements have been replaced by the use of explicit
+equality constraints that are used in conjunction with implication constraints
+to express the local scope of GADT refinements.
\begin{code}
-- Running example:
--- MkT :: forall a b c. (a:=:[b]) => b -> c -> T a
+-- MkT :: forall a b c. (a~[b]) => b -> c -> T a
-- with scrutinee of type (T ty)
-tcConPat :: PatState -> SrcSpan -> DataCon -> TyCon
- -> BoxySigmaType -- Type of the pattern
- -> HsConPatDetails Name -> (PatState -> TcM a)
- -> TcM (Pat TcId, [TcTyVar], a)
-tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
- = do { let (univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _) = dataConFullSig data_con
- skol_info = PatSkol data_con
- origin = SigOrigin skol_info
+tcConPat :: PatEnv -> Located Name
+ -> TcRhoType -- Type of the pattern
+ -> HsConPatDetails Name -> TcM a
+ -> TcM (Pat TcId, a)
+tcConPat penv (L con_span con_name) pat_ty arg_pats thing_inside
+ = do { data_con <- tcLookupDataCon con_name
+ ; let tycon = dataConTyCon data_con
+ -- For data families this is the representation tycon
+ (univ_tvs, ex_tvs, eq_spec, theta, arg_tys, _)
+ = dataConFullSig data_con
-- Instantiate the constructor type variables [a->ty]
- ; ctxt_res_tys <- boxySplitTyConAppWithFamily tycon pat_ty
- ; ex_tvs' <- tcInstSkolTyVars skol_info ex_tvs -- Get location from monad,
- -- not from ex_tvs
- ; let tenv = zipTopTvSubst (univ_tvs ++ ex_tvs)
+ -- This may involve doing a family-instance coercion,
+ -- and building a wrapper
+ ; (wrap, ctxt_res_tys) <- matchExpectedPatTy (matchExpectedConTy tycon) pat_ty
+
+ -- Add the stupid theta
+ ; setSrcSpan con_span $ addDataConStupidTheta data_con ctxt_res_tys
+
+ ; checkExistentials ex_tvs penv
+ ; ex_tvs' <- tcInstSuperSkolTyVars ex_tvs
+ -- Get location from monad, not from ex_tvs
+
+ ; let pat_ty' = mkTyConApp tycon ctxt_res_tys
+ -- pat_ty' is type of the actual constructor application
+ -- pat_ty' /= pat_ty iff coi /= IdCo
+
+ tenv = zipTopTvSubst (univ_tvs ++ ex_tvs)
(ctxt_res_tys ++ mkTyVarTys ex_tvs')
- eq_spec' = substEqSpec tenv eq_spec
- theta' = substTheta tenv (eq_theta ++ dict_theta)
- arg_tys' = substTys tenv arg_tys
+ arg_tys' = substTys tenv arg_tys
+
+ ; if null ex_tvs && null eq_spec && null theta
+ then do { -- The common case; no class bindings etc
+ -- (see Note [Arrows and patterns])
+ (arg_pats', res) <- tcConArgs data_con arg_tys'
+ arg_pats penv thing_inside
+ ; let res_pat = ConPatOut { pat_con = L con_span data_con,
+ pat_tvs = [], pat_dicts = [],
+ pat_binds = emptyTcEvBinds,
+ pat_args = arg_pats',
+ pat_ty = pat_ty' }
+
+ ; return (mkHsWrapPat wrap res_pat pat_ty, res) }
+
+ else do -- The general case, with existential,
+ -- and local equality constraints
+ { let theta' = substTheta tenv (eqSpecPreds eq_spec ++ theta)
+ -- order is *important* as we generate the list of
+ -- dictionary binders from theta'
+ no_equalities = not (any isEqPred theta')
+ skol_info = case pe_ctxt penv of
+ LamPat mc -> PatSkol data_con mc
+ LetPat {} -> UnkSkol -- Doesn't matter
+
+ ; gadts_on <- xoptM Opt_GADTs
+ ; checkTc (no_equalities || gadts_on)
+ (ptext (sLit "A pattern match on a GADT requires -XGADTs"))
+ -- Trac #2905 decided that a *pattern-match* of a GADT
+ -- should require the GADT language flag
+
+ ; given <- newEvVars theta'
+ ; (ev_binds, (arg_pats', res))
+ <- checkConstraints skol_info ex_tvs' given $
+ tcConArgs data_con arg_tys' arg_pats penv thing_inside
+
+ ; let res_pat = ConPatOut { pat_con = L con_span data_con,
+ pat_tvs = ex_tvs',
+ pat_dicts = given,
+ pat_binds = ev_binds,
+ pat_args = arg_pats',
+ pat_ty = pat_ty' }
+ ; return (mkHsWrapPat wrap res_pat pat_ty, res)
+ } }
+
+----------------------------
+matchExpectedPatTy :: (TcRhoType -> TcM (Coercion, a))
+ -> TcRhoType -> TcM (HsWrapper, a)
+-- See Note [Matching polytyped patterns]
+-- Returns a wrapper : pat_ty ~ inner_ty
+matchExpectedPatTy inner_match pat_ty
+ | null tvs && null theta
+ = do { (coi, res) <- inner_match pat_ty
+ ; return (coToHsWrapper (mkSymCo coi), res) }
+ -- The Sym is because the inner_match returns a coercion
+ -- that is the other way round to matchExpectedPatTy
- ; co_vars <- newCoVars eq_spec' -- Make coercion variables
- ; pstate' <- refineAlt data_con pstate ex_tvs' co_vars pat_ty
-
- ; ((arg_pats', inner_tvs, res), lie_req) <- getLIE $
- tcConArgs data_con arg_tys' arg_pats pstate' thing_inside
-
- ; loc <- getInstLoc origin
- ; dicts <- newDictBndrs loc theta'
- ; dict_binds <- tcSimplifyCheckPat loc co_vars (pat_reft pstate')
- ex_tvs' dicts lie_req
-
- ; addDataConStupidTheta data_con ctxt_res_tys
-
- ; return
- (unwrapFamInstScrutinee tycon ctxt_res_tys $
- ConPatOut { pat_con = L con_span data_con,
- pat_tvs = ex_tvs' ++ co_vars,
- pat_dicts = map instToVar dicts,
- pat_binds = dict_binds,
- pat_args = arg_pats', pat_ty = pat_ty },
- ex_tvs' ++ inner_tvs, res)
- }
+ | otherwise
+ = do { (_, tys, subst) <- tcInstTyVars tvs
+ ; wrap1 <- instCall PatOrigin tys (substTheta subst theta)
+ ; (wrap2, arg_tys) <- matchExpectedPatTy inner_match (TcType.substTy subst tau)
+ ; return (wrap2 <.> wrap1 , arg_tys) }
where
- -- Split against the family tycon if the pattern constructor
- -- belongs to a family instance tycon.
- boxySplitTyConAppWithFamily tycon pat_ty =
- traceTc traceMsg >>
- case tyConFamInst_maybe tycon of
- Nothing -> boxySplitTyConApp tycon pat_ty
- Just (fam_tycon, instTys) ->
- do { scrutinee_arg_tys <- boxySplitTyConApp fam_tycon pat_ty
- ; (_, freshTvs, subst) <- tcInstTyVars (tyConTyVars tycon)
- ; boxyUnifyList (substTys subst instTys) scrutinee_arg_tys
- ; return freshTvs
- }
- where
- traceMsg = sep [ text "tcConPat:boxySplitTyConAppWithFamily:" <+>
- ppr tycon <+> ppr pat_ty
- , text " family instance:" <+>
- ppr (tyConFamInst_maybe tycon)
- ]
-
- -- Wraps the pattern (which must be a ConPatOut pattern) in a coercion
- -- pattern if the tycon is an instance of a family.
- --
- unwrapFamInstScrutinee :: TyCon -> [Type] -> Pat Id -> Pat Id
- unwrapFamInstScrutinee tycon args pat
- | Just co_con <- tyConFamilyCoercion_maybe tycon
--- , not (isNewTyCon tycon) -- newtypes are explicitly unwrapped by
- -- the desugarer
- -- NB: We can use CoPat directly, rather than mkCoPat, as we know the
- -- coercion is not the identity; mkCoPat is inconvenient as it
- -- wants a located pattern.
- = CoPat (WpCo $ mkTyConApp co_con args) -- co fam ty to repr ty
- (pat {pat_ty = mkTyConApp tycon args}) -- representation type
- pat_ty -- family inst type
- | otherwise
- = pat
+ (tvs, theta, tau) = tcSplitSigmaTy pat_ty
+
+----------------------------
+matchExpectedConTy :: TyCon -- The TyCon that this data
+ -- constructor actually returns
+ -> TcRhoType -- The type of the pattern
+ -> TcM (Coercion, [TcSigmaType])
+-- See Note [Matching constructor patterns]
+-- Returns a coercion : T ty1 ... tyn ~ pat_ty
+-- This is the same way round as matchExpectedListTy etc
+-- but the other way round to matchExpectedPatTy
+matchExpectedConTy data_tc pat_ty
+ | Just (fam_tc, fam_args, co_tc) <- tyConFamInstSig_maybe data_tc
+ -- Comments refer to Note [Matching constructor patterns]
+ -- co_tc :: forall a. T [a] ~ T7 a
+ = do { (_, tys, subst) <- tcInstTyVars (tyConTyVars data_tc)
+ -- tys = [ty1,ty2]
+
+ ; coi1 <- unifyType (mkTyConApp fam_tc (substTys subst fam_args)) pat_ty
+ -- coi1 : T (ty1,ty2) ~ pat_ty
+
+ ; let coi2 = mkAxInstCo co_tc tys
+ -- coi2 : T (ty1,ty2) ~ T7 ty1 ty2
+
+ ; return (mkTransCo (mkSymCo coi2) coi1, tys) }
+ | otherwise
+ = matchExpectedTyConApp data_tc pat_ty
+ -- coi : T tys ~ pat_ty
+\end{code}
+Note [Matching constructor patterns]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Suppose (coi, tys) = matchExpectedConType data_tc pat_ty
+
+ * In the simple case, pat_ty = tc tys
+
+ * If pat_ty is a polytype, we want to instantiate it
+ This is like part of a subsumption check. Eg
+ f :: (forall a. [a]) -> blah
+ f [] = blah
+
+ * In a type family case, suppose we have
+ data family T a
+ data instance T (p,q) = A p | B q
+ Then we'll have internally generated
+ data T7 p q = A p | B q
+ axiom coT7 p q :: T (p,q) ~ T7 p q
+
+ So if pat_ty = T (ty1,ty2), we return (coi, [ty1,ty2]) such that
+ coi = coi2 . coi1 : T7 t ~ pat_ty
+ coi1 : T (ty1,ty2) ~ pat_ty
+ coi2 : T7 ty1 ty2 ~ T (ty1,ty2)
+
+ For families we do all this matching here, not in the unifier,
+ because we never want a whisper of the data_tycon to appear in
+ error messages; it's a purely internal thing
+
+\begin{code}
tcConArgs :: DataCon -> [TcSigmaType]
-> Checker (HsConPatDetails Name) (HsConPatDetails Id)
-tcConArgs data_con arg_tys (PrefixCon arg_pats) pstate thing_inside
+tcConArgs data_con arg_tys (PrefixCon arg_pats) penv thing_inside
= do { checkTc (con_arity == no_of_args) -- Check correct arity
(arityErr "Constructor" data_con con_arity no_of_args)
; let pats_w_tys = zipEqual "tcConArgs" arg_pats arg_tys
- ; (arg_pats', tvs, res) <- tcMultiple tcConArg pats_w_tys
- pstate thing_inside
- ; return (PrefixCon arg_pats', tvs, res) }
+ ; (arg_pats', res) <- tcMultiple tcConArg pats_w_tys
+ penv thing_inside
+ ; return (PrefixCon arg_pats', res) }
where
con_arity = dataConSourceArity data_con
no_of_args = length arg_pats
-tcConArgs data_con [arg_ty1,arg_ty2] (InfixCon p1 p2) pstate thing_inside
+tcConArgs data_con arg_tys (InfixCon p1 p2) penv thing_inside
= do { checkTc (con_arity == 2) -- Check correct arity
(arityErr "Constructor" data_con con_arity 2)
- ; ([p1',p2'], tvs, res) <- tcMultiple tcConArg [(p1,arg_ty1),(p2,arg_ty2)]
- pstate thing_inside
- ; return (InfixCon p1' p2', tvs, res) }
+ ; let [arg_ty1,arg_ty2] = arg_tys -- This can't fail after the arity check
+ ; ([p1',p2'], res) <- tcMultiple tcConArg [(p1,arg_ty1),(p2,arg_ty2)]
+ penv thing_inside
+ ; return (InfixCon p1' p2', res) }
where
con_arity = dataConSourceArity data_con
-tcConArgs data_con other_args (InfixCon p1 p2) pstate thing_inside
- = pprPanic "tcConArgs" (ppr data_con) -- InfixCon always has two arguments
-
-tcConArgs data_con arg_tys (RecCon (HsRecFields rpats dd)) pstate thing_inside
- = do { (rpats', tvs, res) <- tcMultiple tc_field rpats pstate thing_inside
- ; return (RecCon (HsRecFields rpats' dd), tvs, res) }
+tcConArgs data_con arg_tys (RecCon (HsRecFields rpats dd)) penv thing_inside
+ = do { (rpats', res) <- tcMultiple tc_field rpats penv thing_inside
+ ; return (RecCon (HsRecFields rpats' dd), res) }
where
tc_field :: Checker (HsRecField FieldLabel (LPat Name)) (HsRecField TcId (LPat TcId))
- tc_field (HsRecField field_lbl pat pun) pstate thing_inside
+ tc_field (HsRecField field_lbl pat pun) penv thing_inside
= do { (sel_id, pat_ty) <- wrapLocFstM find_field_ty field_lbl
- ; (pat', tvs, res) <- tcConArg (pat, pat_ty) pstate thing_inside
- ; return (HsRecField sel_id pat' pun, tvs, res) }
+ ; (pat', res) <- tcConArg (pat, pat_ty) penv thing_inside
+ ; return (HsRecField sel_id pat' pun, res) }
find_field_ty :: FieldLabel -> TcM (Id, TcType)
find_field_ty field_lbl
-- dataConFieldLabels will be empty (and each field in the pattern
-- will generate an error below).
-tcConArg :: Checker (LPat Name, BoxySigmaType) (LPat Id)
-tcConArg (arg_pat, arg_ty) pstate thing_inside
- = tc_lpat arg_pat arg_ty pstate thing_inside
- -- NB: the tc_lpat will refine pat_ty if necessary
- -- based on the current pstate, which may include
- -- refinements from peer argument patterns to the left
+tcConArg :: Checker (LPat Name, TcSigmaType) (LPat Id)
+tcConArg (arg_pat, arg_ty) penv thing_inside
+ = tc_lpat arg_pat arg_ty penv thing_inside
\end{code}
\begin{code}
-- The origin should always report "occurrence of C"
-- even when C occurs in a pattern
stupid_theta = dataConStupidTheta data_con
- tenv = zipTopTvSubst (dataConUnivTyVars data_con) inst_tys
+ tenv = mkTopTvSubst (dataConUnivTyVars data_con `zip` inst_tys)
+ -- NB: inst_tys can be longer than the univ tyvars
+ -- because the constructor might have existentials
inst_theta = substTheta tenv stupid_theta
\end{code}
-
-%************************************************************************
-%* *
- Type refinement
-%* *
-%************************************************************************
-
-\begin{code}
-refineAlt :: DataCon -- For tracing only
- -> PatState
- -> [TcTyVar] -- Existentials
- -> [CoVar] -- Equational constraints
- -> BoxySigmaType -- Pattern type
- -> TcM PatState
-
-refineAlt con pstate ex_tvs [] pat_ty
- | null $ dataConEqTheta con
- = return pstate -- Common case: no equational constraints
-
-refineAlt con pstate ex_tvs co_vars pat_ty
- = do { opt_gadt <- doptM Opt_GADTs -- No type-refinement unless GADTs are on
- ; if (not opt_gadt) then return pstate
- else do
-
- { checkTc (isRigidTy pat_ty) (nonRigidMatch con)
- -- We are matching against a GADT constructor with non-trivial
- -- constraints, but pattern type is wobbly. For now we fail.
- -- We can make sense of this, however:
- -- Suppose MkT :: forall a b. (a:=:[b]) => b -> T a
- -- (\x -> case x of { MkT v -> v })
- -- We can infer that x must have type T [c], for some wobbly 'c'
- -- and translate to
- -- (\(x::T [c]) -> case x of
- -- MkT b (g::([c]:=:[b])) (v::b) -> v `cast` sym g
- -- To implement this, we'd first instantiate the equational
- -- constraints with *wobbly* type variables for the existentials;
- -- then unify these constraints to make pat_ty the right shape;
- -- then proceed exactly as in the rigid case
-
- -- In the rigid case, we perform type refinement
- ; case gadtRefine (pat_reft pstate) ex_tvs co_vars of {
- Failed msg -> failWithTc (inaccessibleAlt msg) ;
- Succeeded reft -> do { traceTc trace_msg
- ; return (pstate { pat_reft = reft, pat_eqs = (pat_eqs pstate || not (null $ dataConEqTheta con)) }) }
- -- DO NOT refine the envt right away, because we
- -- might be inside a lazy pattern. Instead, refine pstate
- where
-
- trace_msg = text "refineAlt:match" <+>
- vcat [ ppr con <+> ppr ex_tvs,
- ppr [(v, tyVarKind v) | v <- co_vars],
- ppr reft]
- } } }
-\end{code}
-
-
-%************************************************************************
-%* *
- Overloaded literals
-%* *
-%************************************************************************
-
-In tcOverloadedLit we convert directly to an Int or Integer if we
-know that's what we want. This may save some time, by not
-temporarily generating overloaded literals, but it won't catch all
-cases (the rest are caught in lookupInst).
-
-\begin{code}
-tcOverloadedLit :: InstOrigin
- -> HsOverLit Name
- -> BoxyRhoType
- -> TcM (HsOverLit TcId)
-tcOverloadedLit orig lit@(HsIntegral i fi) res_ty
- | not (fi `isHsVar` fromIntegerName) -- Do not generate a LitInst for rebindable syntax.
- -- Reason: If we do, tcSimplify will call lookupInst, which
- -- will call tcSyntaxName, which does unification,
- -- which tcSimplify doesn't like
- -- ToDo: noLoc sadness
- = do { integer_ty <- tcMetaTy integerTyConName
- ; fi' <- tcSyntaxOp orig fi (mkFunTy integer_ty res_ty)
- ; return (HsIntegral i (HsApp (noLoc fi') (nlHsLit (HsInteger i integer_ty)))) }
-
- | Just expr <- shortCutIntLit i res_ty
- = return (HsIntegral i expr)
-
- | otherwise
- = do { expr <- newLitInst orig lit res_ty
- ; return (HsIntegral i expr) }
-
-tcOverloadedLit orig lit@(HsFractional r fr) res_ty
- | not (fr `isHsVar` fromRationalName) -- c.f. HsIntegral case
- = do { rat_ty <- tcMetaTy rationalTyConName
- ; fr' <- tcSyntaxOp orig fr (mkFunTy rat_ty res_ty)
- -- Overloaded literals must have liftedTypeKind, because
- -- we're instantiating an overloaded function here,
- -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
- -- However this'll be picked up by tcSyntaxOp if necessary
- ; return (HsFractional r (HsApp (noLoc fr') (nlHsLit (HsRat r rat_ty)))) }
-
- | Just expr <- shortCutFracLit r res_ty
- = return (HsFractional r expr)
-
- | otherwise
- = do { expr <- newLitInst orig lit res_ty
- ; return (HsFractional r expr) }
-
-tcOverloadedLit orig lit@(HsIsString s fr) res_ty
- | not (fr `isHsVar` fromStringName) -- c.f. HsIntegral case
- = do { str_ty <- tcMetaTy stringTyConName
- ; fr' <- tcSyntaxOp orig fr (mkFunTy str_ty res_ty)
- ; return (HsIsString s (HsApp (noLoc fr') (nlHsLit (HsString s)))) }
-
- | Just expr <- shortCutStringLit s res_ty
- = return (HsIsString s expr)
-
- | otherwise
- = do { expr <- newLitInst orig lit res_ty
- ; return (HsIsString s expr) }
-
-newLitInst :: InstOrigin -> HsOverLit Name -> BoxyRhoType -> TcM (HsExpr TcId)
-newLitInst orig lit res_ty -- Make a LitInst
- = do { loc <- getInstLoc orig
- ; res_tau <- zapToMonotype res_ty
- ; new_uniq <- newUnique
- ; let lit_nm = mkSystemVarName new_uniq FSLIT("lit")
- lit_inst = LitInst {tci_name = lit_nm, tci_lit = lit,
- tci_ty = res_tau, tci_loc = loc}
- ; extendLIE lit_inst
- ; return (HsVar (instToId lit_inst)) }
-\end{code}
-
+Note [Arrows and patterns]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+(Oct 07) Arrow noation has the odd property that it involves
+"holes in the scope". For example:
+ expr :: Arrow a => a () Int
+ expr = proc (y,z) -> do
+ x <- term -< y
+ expr' -< x
+
+Here the 'proc (y,z)' binding scopes over the arrow tails but not the
+arrow body (e.g 'term'). As things stand (bogusly) all the
+constraints from the proc body are gathered together, so constraints
+from 'term' will be seen by the tcPat for (y,z). But we must *not*
+bind constraints from 'term' here, becuase the desugarer will not make
+these bindings scope over 'term'.
+
+The Right Thing is not to confuse these constraints together. But for
+now the Easy Thing is to ensure that we do not have existential or
+GADT constraints in a 'proc', and to short-cut the constraint
+simplification for such vanilla patterns so that it binds no
+constraints. Hence the 'fast path' in tcConPat; but it's also a good
+plan for ordinary vanilla patterns to bypass the constraint
+simplification step.
%************************************************************************
%* *
%* *
%************************************************************************
-\begin{code}
-patCtxt :: Pat Name -> Maybe Message -- Not all patterns are worth pushing a context
-patCtxt (VarPat _) = Nothing
-patCtxt (ParPat _) = Nothing
-patCtxt (AsPat _ _) = Nothing
-patCtxt pat = Just (hang (ptext SLIT("In the pattern:"))
- 4 (ppr pat))
-
------------------------------------------------
-
-existentialExplode pat
- = hang (vcat [text "My brain just exploded.",
- text "I can't handle pattern bindings for existentially-quantified constructors.",
- text "Instead, use a case-expression, or do-notation, to unpack the constructor.",
- text "In the binding group for"])
- 4 (ppr pat)
+{- This was used to improve the error message from
+ an existential escape. Need to think how to do this.
+sigPatCtxt :: [LPat Var] -> [Var] -> [TcType] -> TcType -> TidyEnv
+ -> TcM (TidyEnv, SDoc)
sigPatCtxt pats bound_tvs pat_tys body_ty tidy_env
= do { pat_tys' <- mapM zonkTcType pat_tys
; body_ty' <- zonkTcType body_ty
(env2, tidy_pat_tys) = tidyOpenTypes env1 pat_tys'
(env3, tidy_body_ty) = tidyOpenType env2 body_ty'
; return (env3,
- sep [ptext SLIT("When checking an existential match that binds"),
- nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)),
- ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
- ptext SLIT("The body has type:") <+> ppr tidy_body_ty
+ sep [ptext (sLit "When checking an existential match that binds"),
+ nest 2 (vcat (zipWith ppr_id show_ids tidy_tys)),
+ ptext (sLit "The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
+ ptext (sLit "The body has type:") <+> ppr tidy_body_ty
]) }
where
bound_ids = collectPatsBinders pats
ppr_id id ty = ppr id <+> dcolon <+> ppr ty
-- Don't zonk the types so we get the separate, un-unified versions
+-}
+
+\begin{code}
+maybeWrapPatCtxt :: Pat Name -> (TcM a -> TcM b) -> TcM a -> TcM b
+-- Not all patterns are worth pushing a context
+maybeWrapPatCtxt pat tcm thing_inside
+ | not (worth_wrapping pat) = tcm thing_inside
+ | otherwise = addErrCtxt msg $ tcm $ popErrCtxt thing_inside
+ -- Remember to pop before doing thing_inside
+ where
+ worth_wrapping (VarPat {}) = False
+ worth_wrapping (ParPat {}) = False
+ worth_wrapping (AsPat {}) = False
+ worth_wrapping _ = True
+ msg = hang (ptext (sLit "In the pattern:")) 2 (ppr pat)
+
+-----------------------------------------------
+checkExistentials :: [TyVar] -> PatEnv -> TcM ()
+ -- See Note [Arrows and patterns]
+checkExistentials [] _ = return ()
+checkExistentials _ (PE { pe_ctxt = LetPat {}}) = failWithTc existentialLetPat
+checkExistentials _ (PE { pe_ctxt = LamPat ProcExpr }) = failWithTc existentialProcPat
+checkExistentials _ (PE { pe_lazy = True }) = failWithTc existentialLazyPat
+checkExistentials _ _ = return ()
+
+existentialLazyPat :: SDoc
+existentialLazyPat
+ = hang (ptext (sLit "An existential or GADT data constructor cannot be used"))
+ 2 (ptext (sLit "inside a lazy (~) pattern"))
+
+existentialProcPat :: SDoc
+existentialProcPat
+ = ptext (sLit "Proc patterns cannot use existential or GADT data constructors")
+
+existentialLetPat :: SDoc
+existentialLetPat
+ = vcat [text "My brain just exploded",
+ text "I can't handle pattern bindings for existential or GADT data constructors.",
+ text "Instead, use a case-expression, or do-notation, to unpack the constructor."]
badFieldCon :: DataCon -> Name -> SDoc
badFieldCon con field
- = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
- ptext SLIT("does not have field"), quotes (ppr field)]
+ = hsep [ptext (sLit "Constructor") <+> quotes (ppr con),
+ ptext (sLit "does not have field"), quotes (ppr field)]
polyPatSig :: TcType -> SDoc
polyPatSig sig_ty
- = hang (ptext SLIT("Illegal polymorphic type signature in pattern:"))
- 4 (ppr sig_ty)
+ = hang (ptext (sLit "Illegal polymorphic type signature in pattern:"))
+ 2 (ppr sig_ty)
-badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
-
-lazyPatErr pat tvs
+lazyUnliftedPatErr :: OutputableBndr name => Pat name -> TcM ()
+lazyUnliftedPatErr pat
= failWithTc $
- hang (ptext SLIT("A lazy (~) pattern cannot bind existential type variables"))
- 2 (vcat (map pprSkolTvBinding tvs))
-
-nonRigidMatch con
- = hang (ptext SLIT("GADT pattern match in non-rigid context for") <+> quotes (ppr con))
- 2 (ptext SLIT("Tell GHC HQ if you'd like this to unify the context"))
-
-nonRigidResult res_ty
- = hang (ptext SLIT("GADT pattern match with non-rigid result type") <+> quotes (ppr res_ty))
- 2 (ptext SLIT("Tell GHC HQ if you'd like this to unify the context"))
+ hang (ptext (sLit "A lazy (~) pattern cannot contain unlifted types:"))
+ 2 (ppr pat)
-inaccessibleAlt msg
- = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg
-\end{code}
-
-\begin{code}
-wrapPatCoI :: CoercionI -> Pat a -> TcType -> Pat a
-wrapPatCoI IdCo pat ty = pat
-wrapPatCoI (ACo co) pat ty = CoPat (WpCo co) pat ty
+unboxedTupleErr :: SDoc -> Type -> SDoc
+unboxedTupleErr what ty
+ = hang (what <+> ptext (sLit "cannot have an unboxed tuple type:"))
+ 2 (ppr ty)
\end{code}
projects / ghc-hetmet.git / blobdiff