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,
+module TcPat ( tcLetPat, tcPat, tcPats, tcOverloadedLit,
addDataConStupidTheta, badFieldCon, polyPatSig ) where
#include "HsVersions.h"
-import {-# SOURCE #-} TcExpr( tcSyntaxOp )
+import {-# SOURCE #-} TcExpr( tcSyntaxOp, tcInferRho)
import HsSyn
import TcHsSyn
import TcEnv
import TcMType
import TcType
+import VarEnv
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 ( DynFlag( Opt_GADTs ) )
import SrcLoc
import ErrUtils
import Util
import Maybes
import Outputable
import FastString
+import Monad
\end{code}
\begin{code}
tcLetPat :: (Name -> Maybe TcRhoType)
-> LPat Name -> BoxySigmaType
- -> TcM a
+ -> 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,
+ = do { let init_state = PS { pat_ctxt = LetPat sig_fn,
pat_eqs = False }
- ; (pat', ex_tvs, res) <- tc_lpat pat pat_ty init_state (\ _ -> thing_inside)
+ ; (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) }
-----------------
-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,
+ -> [BoxySigmaType] -- and their types
+ -> BoxyRhoType -- Result type,
+ -> (BoxyRhoType -> 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
-
-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
+-- 3. Check the body
+-- 4. Check that no existentials escape
+
+tcPats ctxt pats tys res_ty thing_inside
+ = tc_lam_pats (APat ctxt) (zipEqual "tcLamPats" pats tys)
+ res_ty thing_inside
+
+tcPat :: HsMatchContext Name
+ -> LPat Name -> BoxySigmaType
+ -> BoxyRhoType -- Result type
+ -> (BoxyRhoType -> TcM a) -- Checker for body, given
+ -- its result type
+ -> TcM (LPat TcId, a)
+tcPat ctxt = tc_lam_pat (APat ctxt)
+
+tc_lam_pat :: PatCtxt -> LPat Name -> BoxySigmaType -> BoxyRhoType
+ -> (BoxyRhoType -> TcM a) -> TcM (LPat TcId, a)
+tc_lam_pat ctxt pat pat_ty res_ty thing_inside
+ = do { ([pat'],thing) <- tc_lam_pats ctxt [(pat, pat_ty)] res_ty thing_inside
; return (pat', thing) }
-----------------
-tc_lam_pats :: [(LPat Name,BoxySigmaType)]
- -> (Refinement,BoxyRhoType) -- Result type
- -> ((Refinement,BoxyRhoType) -> TcM a) -- Checker for body, given its result type
+tc_lam_pats :: PatCtxt
+ -> [(LPat Name,BoxySigmaType)]
+ -> BoxyRhoType -- Result type
+ -> (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 }
+tc_lam_pats ctxt pat_ty_prs res_ty thing_inside
+ = do { let init_state = PS { pat_ctxt = ctxt, pat_eqs = False }
- ; (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)
+ ; (pats', ex_tvs, res) <- do { traceTc (text "tc_lam_pats" <+> (ppr pat_ty_prs $$ ppr res_ty))
+ ; tcMultiple tc_lpat_pr pat_ty_prs init_state $ \ pstate' ->
+ if (pat_eqs pstate' && (not $ isRigidTy res_ty))
+ then nonRigidResult ctxt res_ty
+ else thing_inside res_ty }
; let tys = map snd pat_ty_prs
; tcCheckExistentialPat pats' ex_tvs tys res_ty
- ; returnM (pats', res) }
+ ; return (pats', res) }
-----------------
-- 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
+tcCheckExistentialPat _ [] _ _
= return () -- Short cut for case when there are no existentials
tcCheckExistentialPat pats ex_tvs pat_tys body_ty
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
+ pat_eqs :: Bool -- <=> there are any equational constraints
+ -- Used at the end to say whether the result
+ -- type must be rigid
}
data PatCtxt
- = LamPat
+ = APat (HsMatchContext Name)
| LetPat (Name -> Maybe TcRhoType) -- Used for let(rec) bindings
+notProcPat :: PatCtxt -> Bool
+notProcPat (APat ProcExpr) = False
+notProcPat _ = True
+
patSigCtxt :: PatState -> UserTypeCtxt
patSigCtxt (PS { pat_ctxt = LetPat _ }) = BindPatSigCtxt
-patSigCtxt other = LamPatSigCtxt
+patSigCtxt _ = LamPatSigCtxt
\end{code}
\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
; mono_name <- newLocalName bndr_name
; return (Id.mkLocalId mono_name pat_ty') }
+tcPatBndr (PS { pat_ctxt = _lam_or_proc }) 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') }
+
-------------------
bindInstsOfPatId :: TcId -> TcM a -> TcM (a, LHsBinds TcId)
; 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"))
+unBoxPatBndrType :: BoxyType -> Name -> TcM TcType
+unBoxPatBndrType ty name = unBoxArgType ty (ptext (sLit "The variable") <+> quotes (ppr name))
+
+unBoxWildCardType :: BoxyType -> TcM TcType
+unBoxWildCardType ty = unBoxArgType ty (ptext (sLit "A wild-card pattern"))
+
+unBoxViewPatType :: BoxyType -> Pat Name -> TcM TcType
+unBoxViewPatType ty pat = unBoxArgType ty (ptext (sLit "The view pattern") <+> ppr pat)
unBoxArgType :: BoxyType -> SDoc -> TcM TcType
-- In addition to calling unbox, unBoxArgType ensures that the type is of ArgTypeKind;
; unifyType ty' ty2
; return ty' }}
where
- msg = pp_this <+> ptext SLIT("cannot be bound to an unboxed tuple")
+ msg = pp_this <+> ptext (sLit "cannot be bound to an unboxed tuple")
\end{code}
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) }
+ do { (pat', tvs, res) <- tc_pat pstate pat pat_ty thing_inside
+ ; return (L span pat', tvs, res) }
--------------------
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
+ -> 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
-- getLIE/extendLIEs: see Note [Hopping the LIE in lazy patterns]
-- Check no existentials
- ; if (null pat_tvs) then return ()
- else lazyPatErr lpat pat_tvs
+ ; unless (null pat_tvs) $ lazyPatErr lpat pat_tvs
+
+ -- Check there are no unlifted types under the lazy pattern
+ ; when (any (isUnLiftedType . idType) $ collectPatBinders pat') $
+ lazyUnliftedPatErr lpat
-- Check that the pattern has a lifted type
; pat_tv <- newBoxyTyVar liftedTypeKind
; return (LazyPat pat', [], res) }
+tc_pat _ p@(QuasiQuotePat _) _ _
+ = pprPanic "Should never see QuasiQuotePat in type checker" (ppr p)
+
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
-- If you fix it, don't forget the bindInstsOfPatIds!
; return (AsPat (L nm_loc bndr_id) pat', tvs, res) }
+tc_pat pstate (orig@(ViewPat expr pat _)) overall_pat_ty thing_inside
+ = do { -- 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`
+ ; let expr'_expected = \ pat_ty -> (mkFunTy overall_pat_ty pat_ty)
+ -- tcSubExp: expected first, offered second
+ -- returns coercion
+ --
+ -- 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_coerc, pat_ty) <- tcInfer $ \ pat_ty ->
+ tcSubExp ViewPatOrigin (expr'_expected pat_ty) expr'_inferred
+
+ -- pattern must have pat_ty
+ ; (pat', tvs, res) <- tc_lpat pat pat_ty pstate thing_inside
+ -- this should get zonked later on, but we unBox it here
+ -- so that we do the same checks as above
+ ; annotation_ty <- unBoxViewPatType overall_pat_ty orig
+ ; return (ViewPat (mkLHsWrap expr_coerc expr') pat' annotation_ty, tvs, 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
+ = do { (inner_ty, tv_binds, coi) <- tcPatSig (patSigCtxt pstate) sig_ty
+ pat_ty
+ ; unless (isIdentityCoI coi) $
+ failWithTc (badSigPat 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 pstate pat@(TypePat ty) pat_ty thing_inside
+tc_pat _ pat@(TypePat _) _ _
= failWithTc (badTypePat pat)
------------------------
-- Lists, tuples, arrays
tc_pat pstate (ListPat pats _) pat_ty thing_inside
= do { (elt_ty, coi) <- boxySplitListTy pat_ty
+ ; let scoi = mkSymCoI coi
; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
pats pstate thing_inside
- ; return (mkCoPatCoI coi (ListPat pats' elt_ty) pat_ty, pats_tvs, res) }
+ ; return (mkCoPatCoI scoi (ListPat pats' elt_ty) pat_ty, pats_tvs, res)
+ }
tc_pat pstate (PArrPat pats _) pat_ty thing_inside
= do { (elt_ty, coi) <- boxySplitPArrTy pat_ty
+ ; let scoi = mkSymCoI coi
; (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 (mkCoPatCoI coi (PArrPat pats' elt_ty) pat_ty, pats_tvs, res) }
+ ; when (null pats) (zapToMonotype pat_ty >> return ()) -- c.f. ExplicitPArr in TcExpr
+ ; return (mkCoPatCoI scoi (PArrPat pats' elt_ty) pat_ty, pats_tvs, res)
+ }
tc_pat pstate (TuplePat pats boxity _) pat_ty thing_inside
= do { let tc = tupleTyCon boxity (length pats)
; (arg_tys, coi) <- boxySplitTyConApp tc pat_ty
+ ; let scoi = mkSymCoI coi
; (pats', pats_tvs, res) <- tcMultiple tc_lpat_pr (pats `zip` arg_tys)
pstate thing_inside
| otherwise = unmangled_result
; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
- return (mkCoPatCoI coi possibly_mangled_result pat_ty, pats_tvs, res)
+ return (mkCoPatCoI scoi possibly_mangled_result pat_ty, pats_tvs, res)
}
------------------------
-- Data constructors
-tc_pat pstate pat_in@(ConPatIn (L con_span con_name) arg_pats) pat_ty thing_inside
+tc_pat pstate (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 }
; 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 (mkCoPatCoI (mkSymCoI coi) (LitPat simple_lit) pat_ty,
+ ; return (mkCoPatCoI (mkSymCoI 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 pstate (NPat over_lit mb_neg eq) pat_ty thing_inside
= do { let orig = LiteralOrigin over_lit
; lit' <- tcOverloadedLit orig over_lit pat_ty
; eq' <- tcSyntaxOp orig eq (mkFunTys [pat_ty, pat_ty] boolTy)
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) }
+ ; return (NPat lit' mb_neg' eq', [], res) }
-tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
+tc_pat pstate (NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
= do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
; let pat_ty' = idType bndr_id
orig = LiteralOrigin lit
; 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) }
+ ; return (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
tc_pat _ _other_pat _ _ = panic "tc_pat" -- ConPatOut, SigPatOut, VarPatOut
\end{code}
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
-> 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
+ = 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
+ full_theta = eq_theta ++ dict_theta
-- Instantiate the constructor type variables [a->ty]
- ; (ctxt_res_tys, coi) <- boxySplitTyConAppWithFamily tycon pat_ty
- ; ex_tvs' <- tcInstSkolTyVars skol_info ex_tvs -- Get location from monad,
- -- not from ex_tvs
+ -- This may involve doing a family-instance coercion, and building a
+ -- wrapper
+ ; (ctxt_res_tys, coi, unwrap_ty) <- boxySplitTyConAppWithFamily tycon
+ pat_ty
+ ; let sym_coi = mkSymCoI coi -- boxy split coercion oriented wrongly
+ pat_ty' = mkTyConApp tycon ctxt_res_tys
+ -- pat_ty' /= pat_ty iff coi /= IdCo
+
+ wrap_res_pat res_pat = mkCoPatCoI sym_coi uwScrut pat_ty
+ where
+ uwScrut = unwrapFamInstScrutinee tycon ctxt_res_tys
+ unwrap_ty res_pat
+
+ -- Add the stupid theta
+ ; addDataConStupidTheta data_con ctxt_res_tys
+
+ ; ex_tvs' <- tcInstSkolTyVars skol_info ex_tvs
+ -- Get location from monad, not from ex_tvs
+
; let 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 full_theta
+ then do { -- The common case; no class bindings etc
+ -- (see Note [Arrows and patterns])
+ (arg_pats', inner_tvs, res) <- tcConArgs data_con arg_tys'
+ arg_pats pstate thing_inside
+ ; let res_pat = ConPatOut { pat_con = L con_span data_con,
+ pat_tvs = [], pat_dicts = [],
+ pat_binds = emptyLHsBinds,
+ pat_args = arg_pats',
+ pat_ty = pat_ty' }
+
+ ; return (wrap_res_pat res_pat, inner_tvs, res) }
+
+ else do -- The general case, with existential, and local equality
+ -- constraints
+ { checkTc (notProcPat (pat_ctxt pstate))
+ (existentialProcPat data_con)
+ -- See Note [Arrows and patterns]
+
+ -- Need to test for rigidity if *any* constraints in theta as class
+ -- constraints may have superclass equality constraints. However,
+ -- we don't want to check for rigidity if we got here only because
+ -- ex_tvs was non-null.
+-- ; unless (null theta') $
+ -- FIXME: AT THE MOMENT WE CHEAT! We only perform the rigidity test
+ -- if we explicitly or implicitly (by a GADT def) have equality
+ -- constraints.
+ ; let eq_preds = [mkEqPred (mkTyVarTy tv, ty) | (tv, ty) <- eq_spec]
+ theta' = substTheta tenv (eq_preds ++ full_theta)
+ -- order is *important* as we generate the list of
+ -- dictionary binders from theta'
+ no_equalities = not (any isEqPred theta')
+ pstate' | no_equalities = pstate
+ | otherwise = pstate { pat_eqs = True }
+
+ ; gadts_on <- doptM 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
+
+ ; unless no_equalities $ checkTc (isRigidTy pat_ty) $
+ nonRigidMatch (pat_ctxt pstate) data_con
- ; 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
+ ; dict_binds <- tcSimplifyCheckPat loc ex_tvs' dicts lie_req
- ; addDataConStupidTheta data_con ctxt_res_tys
-
- ; let pat_ty' = mkTyConApp tycon ctxt_res_tys
- -- pat_ty /= pat_ty iff coi /= IdCo
- res_pat = ConPatOut { pat_con = L con_span data_con,
- pat_tvs = ex_tvs' ++ co_vars,
+ ; let res_pat = ConPatOut { pat_con = L con_span data_con,
+ pat_tvs = ex_tvs',
pat_dicts = map instToVar dicts,
pat_binds = dict_binds,
pat_args = arg_pats', pat_ty = pat_ty' }
- ; return
- (mkCoPatCoI coi
- (unwrapFamInstScrutinee tycon ctxt_res_tys res_pat) pat_ty,
- ex_tvs' ++ inner_tvs, res)
- }
+ ; return (wrap_res_pat res_pat, ex_tvs' ++ inner_tvs, res)
+ } }
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
+ Nothing ->
+ do { (scrutinee_arg_tys, coi1) <- boxySplitTyConApp tycon pat_ty
+ ; return (scrutinee_arg_tys, coi1, pat_ty)
+ }
Just (fam_tycon, instTys) ->
- do { (scrutinee_arg_tys, coi) <- boxySplitTyConApp fam_tycon pat_ty
+ do { (scrutinee_arg_tys, coi1) <- boxySplitTyConApp fam_tycon pat_ty
; (_, freshTvs, subst) <- tcInstTyVars (tyConTyVars tycon)
- ; boxyUnifyList (substTys subst instTys) scrutinee_arg_tys
- ; return (freshTvs, coi)
+ ; let instTys' = substTys subst instTys
+ ; cois <- boxyUnifyList instTys' scrutinee_arg_tys
+ ; let coi = if isIdentityCoI coi1
+ then -- pat_ty was splittable
+ -- => boxyUnifyList had real work to do
+ mkTyConAppCoI fam_tycon instTys' cois
+ else -- pat_ty was not splittable
+ -- => scrutinee_arg_tys are fresh tvs and
+ -- boxyUnifyList just instantiated those
+ coi1
+ ; return (freshTvs, coi, mkTyConApp fam_tycon instTys')
+ -- this is /= pat_ty
+ -- iff cois is non-trivial
}
where
traceMsg = sep [ text "tcConPat:boxySplitTyConAppWithFamily:" <+>
-- 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
+ unwrapFamInstScrutinee :: TyCon -> [Type] -> Type -> Pat Id -> Pat Id
+ unwrapFamInstScrutinee tycon args unwrap_ty 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
+ = CoPat (WpCast $ mkTyConApp co_con args) -- co fam ty to repr ty
(pat {pat_ty = mkTyConApp tycon args}) -- representation type
- pat_ty -- family inst type
+ unwrap_ty -- family inst type
| otherwise
= pat
-
tcConArgs :: DataCon -> [TcSigmaType]
-> Checker (HsConPatDetails Name) (HsConPatDetails Id)
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) pstate thing_inside
= do { checkTc (con_arity == 2) -- Check correct arity
(arityErr "Constructor" data_con con_arity 2)
+ ; let [arg_ty1,arg_ty2] = arg_tys -- This can't fail after the arity check
; ([p1',p2'], tvs, res) <- tcMultiple tcConArg [(p1,arg_ty1),(p2,arg_ty2)]
pstate thing_inside
; return (InfixCon p1' p2', tvs, 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) }
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
\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}
+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.
%************************************************************************
-> 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.
+tcOverloadedLit orig lit@(OverLit { ol_val = val, ol_rebindable = rebindable
+ , ol_witness = meth_name }) res_ty
+ | rebindable
+ -- 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)
+ = do { hs_lit <- mkOverLit val
+ ; let lit_ty = hsLitType hs_lit
+ ; fi' <- tcSyntaxOp orig meth_name (mkFunTy lit_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) }
+ ; let witness = HsApp (noLoc fi') (noLoc (HsLit hs_lit))
+ ; return (lit { ol_witness = witness, ol_type = res_ty }) }
-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)
+ | Just expr <- shortCutLit val res_ty
+ = return (lit { ol_witness = expr, ol_type = res_ty })
| 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")
+ ; 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}
+ witness = HsVar (instToId lit_inst)
; extendLIE lit_inst
- ; return (HsVar (instToId lit_inst)) }
+ ; return (lit { ol_witness = witness, ol_type = res_ty }) }
\end{code}
patCtxt (VarPat _) = Nothing
patCtxt (ParPat _) = Nothing
patCtxt (AsPat _ _) = Nothing
-patCtxt pat = Just (hang (ptext SLIT("In the pattern:"))
+patCtxt pat = Just (hang (ptext (sLit "In the pattern:"))
4 (ppr pat))
-----------------------------------------------
+existentialExplode :: LPat Name -> SDoc
existentialExplode pat
= hang (vcat [text "My brain just exploded.",
- text "I can't handle pattern bindings for existentially-quantified constructors.",
+ 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.",
text "In the binding group for"])
4 (ppr pat)
+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"),
+ 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
+ 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
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)
+
+badSigPat :: TcType -> SDoc
+badSigPat pat_ty = ptext (sLit "Pattern signature must exactly match:") <+>
+ ppr pat_ty
+
+badTypePat :: Pat Name -> SDoc
+badTypePat pat = ptext (sLit "Illegal type pattern") <+> ppr pat
-badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
+existentialProcPat :: DataCon -> SDoc
+existentialProcPat con
+ = hang (ptext (sLit "Illegal constructor") <+> quotes (ppr con) <+> ptext (sLit "in a 'proc' pattern"))
+ 2 (ptext (sLit "Proc patterns cannot use existentials or GADTs"))
-lazyPatErr pat tvs
+lazyPatErr :: Pat name -> [TcTyVar] -> TcM ()
+lazyPatErr _ tvs
= failWithTc $
- hang (ptext SLIT("A lazy (~) pattern cannot bind existential type variables"))
+ hang (ptext (sLit "A lazy (~) pattern cannot match existential or GADT data constructors"))
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"))
+lazyUnliftedPatErr :: OutputableBndr name => Pat name -> TcM ()
+lazyUnliftedPatErr pat
+ = failWithTc $
+ hang (ptext (sLit "A lazy (~) pattern cannot contain unlifted types"))
+ 2 (ppr pat)
-inaccessibleAlt msg
- = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg
+nonRigidMatch :: PatCtxt -> DataCon -> SDoc
+nonRigidMatch ctxt con
+ = hang (ptext (sLit "GADT pattern match in non-rigid context for") <+> quotes (ppr con))
+ 2 (ptext (sLit "Probable solution: add a type signature for") <+> what ctxt)
+ where
+ what (APat (FunRhs f _)) = quotes (ppr f)
+ what (APat CaseAlt) = ptext (sLit "the scrutinee of the case expression")
+ what (APat LambdaExpr ) = ptext (sLit "the lambda expression")
+ what (APat (StmtCtxt _)) = ptext (sLit "the right hand side of a do/comprehension binding")
+ what _other = ptext (sLit "something")
+
+nonRigidResult :: PatCtxt -> Type -> TcM a
+nonRigidResult ctxt res_ty
+ = do { env0 <- tcInitTidyEnv
+ ; let (env1, res_ty') = tidyOpenType env0 res_ty
+ msg = hang (ptext (sLit "GADT pattern match with non-rigid result type")
+ <+> quotes (ppr res_ty'))
+ 2 (ptext (sLit "Solution: add a type signature for")
+ <+> what ctxt )
+ ; failWithTcM (env1, msg) }
+ where
+ what (APat (FunRhs f _)) = quotes (ppr f)
+ what (APat CaseAlt) = ptext (sLit "the entire case expression")
+ what (APat LambdaExpr) = ptext (sLit "the lambda exression")
+ what (APat (StmtCtxt _)) = ptext (sLit "the entire do/comprehension expression")
+ what _other = ptext (sLit "something")
\end{code}
projects / ghc-hetmet.git / blobdiff