%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[TcPat]{Typechecking patterns}
\begin{code}
-module TcPat ( tcPat ) where
+module TcPat ( tcPat, tcPats, PatCtxt(..), badFieldCon, polyPatSig ) where
#include "HsVersions.h"
-import HsSyn ( InPat(..), OutPat(..), HsLit(..), HsExpr(..) )
-import RnHsSyn ( RenamedPat )
-import TcHsSyn ( TcPat )
-
-import TcMonad
-import Inst ( Inst, OverloadedLit(..), InstOrigin(..),
- emptyLIE, plusLIE, plusLIEs, LIE,
- newMethod, newOverloadedLit
- )
-import Name ( Name {- instance Outputable -} )
-import TcEnv ( TcIdOcc(..), tcLookupGlobalValue, tcLookupGlobalValueByKey,
- tcLookupLocalValueOK, tcInstId
+import HsSyn ( Pat(..), LPat, HsConDetails(..), HsLit(..), HsOverLit(..),
+ HsExpr(..), LHsBinds, emptyLHsBinds, isEmptyLHsBinds )
+import HsUtils
+import TcHsSyn ( TcId, hsLitType )
+import TcRnMonad
+import Inst ( InstOrigin(..),
+ newMethodFromName, newOverloadedLit, newDicts,
+ instToId, tcInstStupidTheta, tcSyntaxName
)
-import TcType ( TcType, TcMaybe, newTyVarTy, newTyVarTys )
-import Unify ( unifyTauTy, unifyTauTyList, unifyTauTyLists )
-
-import Maybes ( maybeToBool )
-import Bag ( Bag )
+import Id ( Id, idType, mkLocalId )
+import Name ( Name )
+import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
+import TcEnv ( newLocalName, tcExtendIdEnv1, tcExtendTyVarEnv,
+ tcLookupClass, tcLookupDataCon, tcLookupId )
+import TcMType ( newTyFlexiVarTy, arityErr, tcSkolTyVars )
+import TcType ( TcType, TcTyVar, TcSigmaType, TcTauType, zipTopTvSubst,
+ SkolemInfo(PatSkol), isSkolemTyVar, pprSkolemTyVar,
+ mkTyVarTys, mkClassPred, mkTyConApp, isOverloadedTy )
+import Kind ( argTypeKind, liftedTypeKind )
+import TcUnify ( tcSubPat, Expected(..), zapExpectedType,
+ zapExpectedTo, zapToListTy, zapToTyConApp )
+import TcHsType ( UserTypeCtxt(..), TcSigInfo( sig_tau ), TcSigFun, tcHsPatSigType )
+import TysWiredIn ( stringTy, parrTyCon, tupleTyCon )
+import Unify ( MaybeErr(..), tcRefineTys, tcMatchTys )
+import Type ( substTys, substTheta )
import CmdLineOpts ( opt_IrrefutableTuples )
-import Id ( GenId, idType, Id )
-import Kind ( Kind, mkBoxedTypeKind, mkTypeKind )
-import Type ( splitFunTys, splitRhoTy,
- splitFunTy_maybe, splitAlgTyConApp_maybe,
- Type
- )
-import TysPrim ( charPrimTy, intPrimTy, floatPrimTy,
- doublePrimTy, addrPrimTy
- )
-import TysWiredIn ( charTy, stringTy, mkListTy, mkTupleTy, intTy )
-import Unique ( Unique, eqClassOpKey, geClassOpKey, minusClassOpKey )
-import Util ( assertPanic, panic )
+import TyCon ( TyCon )
+import DataCon ( DataCon, dataConTyCon, isVanillaDataCon, dataConInstOrigArgTys,
+ dataConFieldLabels, dataConSourceArity, dataConSig )
+import PrelNames ( eqStringName, eqName, geName, negateName, minusName,
+ integralClassName )
+import BasicTypes ( isBoxed )
+import SrcLoc ( Located(..), SrcSpan, noLoc, unLoc, getLoc )
+import ErrUtils ( Message )
import Outputable
+import FastString
\end{code}
-\begin{code}
-tcPat :: RenamedPat -> TcM s (TcPat s, LIE s, TcType s)
-\end{code}
%************************************************************************
%* *
-\subsection{Variables, wildcards, lazy pats, as-pats}
+ External interface
%* *
%************************************************************************
-\begin{code}
-tcPat (VarPatIn name)
- = tcLookupLocalValueOK "tcPat1:" name `thenNF_Tc` \ id ->
- returnTc (VarPat (TcId id), emptyLIE, idType id)
-
-tcPat (LazyPatIn pat)
- = tcPat pat `thenTc` \ (pat', lie, ty) ->
- returnTc (LazyPat pat', lie, ty)
-
-tcPat pat_in@(AsPatIn name pat)
- = tcLookupLocalValueOK "tcPat2" name `thenNF_Tc` \ id ->
- tcPat pat `thenTc` \ (pat', lie, ty) ->
- tcAddErrCtxt (patCtxt pat_in) $
- unifyTauTy (idType id) ty `thenTc_`
- returnTc (AsPat (TcId id) pat', lie, ty)
-
-tcPat WildPatIn
- = newTyVarTy mkTypeKind `thenNF_Tc` \ tyvar_ty ->
- returnTc (WildPat tyvar_ty, emptyLIE, tyvar_ty)
-
-tcPat (NegPatIn pat)
- = tcPat (negate_lit pat)
- where
- negate_lit (LitPatIn (HsInt i)) = LitPatIn (HsInt (-i))
- negate_lit (LitPatIn (HsFrac f)) = LitPatIn (HsFrac (-f))
- negate_lit _ = panic "TcPat:negate_pat"
+Note [Nesting]
+
+tcPat takes a "thing inside" over which the patter scopes. This is partly
+so that tcPat can extend the environment for the thing_inside, but also
+so that constraints arising in the thing_inside can be discharged by the
+pattern.
-tcPat (ParPatIn parend_pat)
- = tcPat parend_pat
+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 tcPat.
+
+\begin{code}
+tcPat :: PatCtxt
+ -> LPat Name -> Expected TcSigmaType
+ -> TcM a -- Thing inside
+ -> TcM (LPat TcId, -- Translated pattern
+ [TcTyVar], -- Existential binders
+ a) -- Result of thing inside
+
+tcPat ctxt pat exp_ty thing_inside
+ = do { err_ctxt <- getErrCtxt
+ ; maybeAddErrCtxt (patCtxt (unLoc pat)) $
+ tc_lpat ctxt pat exp_ty $
+ setErrCtxt err_ctxt thing_inside }
+ -- Restore error context before doing thing_inside
+ -- See note [Nesting] above
+
+--------------------
+tcPats :: PatCtxt
+ -> [LPat Name]
+ -> [Expected TcSigmaType] -- Excess types discarded
+ -> TcM a
+ -> TcM ([LPat TcId], [TcTyVar], a)
+
+tcPats ctxt [] _ thing_inside
+ = do { res <- thing_inside
+ ; return ([], [], res) }
+
+tcPats ctxt (p:ps) (ty:tys) thing_inside
+ = do { (p', p_tvs, (ps', ps_tvs, res))
+ <- tcPat ctxt p ty $
+ tcPats ctxt ps tys thing_inside
+ ; return (p':ps', p_tvs ++ ps_tvs, res) }
+
+--------------------
+tcCheckPats :: PatCtxt
+ -> [LPat Name] -> [TcSigmaType]
+ -> TcM a
+ -> TcM ([LPat TcId], [TcTyVar], a)
+tcCheckPats ctxt pats tys thing_inside -- A trivial wrapper
+ = tcPats ctxt pats (map Check tys) thing_inside
\end{code}
+
%************************************************************************
%* *
-\subsection{Explicit lists and tuples}
+ Binders
%* *
%************************************************************************
\begin{code}
-tcPat pat_in@(ListPatIn pats)
- = tcPats pats `thenTc` \ (pats', lie, tys) ->
- newTyVarTy mkBoxedTypeKind `thenNF_Tc` \ tyvar_ty ->
- tcAddErrCtxt (patCtxt pat_in) $
- unifyTauTyList (tyvar_ty:tys) `thenTc_`
-
- returnTc (ListPat tyvar_ty pats', lie, mkListTy tyvar_ty)
-
-tcPat pat_in@(TuplePatIn pats)
- = let
- arity = length pats
- in
- tcPats pats `thenTc` \ (pats', lie, tys) ->
-
- -- Make sure we record that the tuples can only contain boxed types
- newTyVarTys arity mkBoxedTypeKind `thenNF_Tc` \ tyvar_tys ->
-
- tcAddErrCtxt (patCtxt pat_in) $
- unifyTauTyLists tyvar_tys tys `thenTc_`
-
- -- possibly do the "make all tuple-pats irrefutable" test:
- let
- unmangled_result = TuplePat pats'
-
- -- 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.
-
- possibly_mangled_result
- = if opt_IrrefutableTuples
- then LazyPat unmangled_result
- else unmangled_result
-
- -- ToDo: IrrefutableEverything
- in
- returnTc (possibly_mangled_result, lie, mkTupleTy arity tys)
+data PatCtxt = LamPat Bool -- Used for lambda, case, do-notation etc
+ | LetPat TcSigFun -- Used for let(rec) bindings
+ -- True <=> we are checking the case expression,
+ -- so can do full-blown refinement
+ -- False <=> inferring, do no refinement
+
+-------------------
+tcPatBndr :: PatCtxt -> Name -> Expected TcSigmaType -> TcM TcId
+tcPatBndr (LamPat _) bndr_name pat_ty
+ = do { pat_ty' <- zapExpectedType pat_ty argTypeKind
+ -- If pat_ty is Expected, this returns the appropriate
+ -- SigmaType. In Infer mode, we create a fresh type variable.
+ -- Note the SigmaType: we can get
+ -- 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 (mkLocalId bndr_name pat_ty') }
+
+tcPatBndr (LetPat lookup_sig) bndr_name pat_ty
+ | Just sig <- lookup_sig bndr_name
+ = do { let mono_ty = sig_tau sig
+ ; mono_name <- newLocalName bndr_name
+ ; tcSubPat mono_ty pat_ty
+ ; return (mkLocalId mono_name mono_ty) }
+
+ | otherwise
+ = do { mono_name <- newLocalName bndr_name
+ ; pat_ty' <- zapExpectedType pat_ty argTypeKind
+ ; return (mkLocalId mono_name pat_ty') }
+
+
+-------------------
+bindInstsOfPatId :: TcId -> TcM a -> TcM (a, LHsBinds TcId)
+bindInstsOfPatId id thing_inside
+ | not (isOverloadedTy (idType id))
+ = do { res <- thing_inside; return (res, emptyLHsBinds) }
+ | otherwise
+ = do { (res, lie) <- getLIE thing_inside
+ ; binds <- bindInstsOfLocalFuns lie [id]
+ ; return (res, binds) }
\end{code}
+
%************************************************************************
%* *
-\subsection{Other constructors}
+ tc_pat: the main worker function
%* *
%************************************************************************
-Constructor patterns are a little fun:
-\begin{itemize}
-\item
-typecheck the arguments
-\item
-look up the constructor
-\item
-specialise its type (ignore the translation this produces)
-\item
-check that the context produced by this specialisation is empty
-\item
-get the arguments out of the function type produced from specialising
-\item
-unify them with the types of the patterns
-\item
-back substitute with the type of the result of the constructor
-\end{itemize}
-
-ToDo: exploit new representation of constructors to make this more
-efficient?
-
\begin{code}
-tcPat pat_in@(ConPatIn name pats)
- = tcPats pats `thenTc` \ (pats', lie, tys) ->
-
- tcAddErrCtxt (patCtxt pat_in) $
- matchConArgTys name tys `thenTc` \ (con_id, data_ty) ->
-
- returnTc (ConPat con_id data_ty pats',
- lie,
- data_ty)
-
-tcPat pat_in@(ConOpPatIn pat1 op _ pat2) -- in binary-op form...
- = tcPat pat1 `thenTc` \ (pat1', lie1, ty1) ->
- tcPat pat2 `thenTc` \ (pat2', lie2, ty2) ->
-
- tcAddErrCtxt (patCtxt pat_in) $
- matchConArgTys op [ty1,ty2] `thenTc` \ (con_id, data_ty) ->
+tc_lpat :: PatCtxt
+ -> LPat Name -> Expected TcSigmaType
+ -> TcM a -- Thing inside
+ -> TcM (LPat TcId, -- Translated pattern
+ [TcTyVar], -- Existential binders
+ a) -- Result of thing inside
+
+tc_lpat ctxt (L span pat) pat_ty thing_inside
+ = setSrcSpan span $
+ -- It's OK to keep setting the SrcSpan;
+ -- it just overwrites the previous value
+ do { (pat', tvs, res) <- tc_pat ctxt pat pat_ty thing_inside
+ ; return (L span pat', tvs, res) }
+
+---------------------
+tc_pat ctxt (VarPat name) pat_ty thing_inside
+ = do { id <- tcPatBndr ctxt name pat_ty
+ ; (res, binds) <- bindInstsOfPatId id $
+ tcExtendIdEnv1 name id $
+ (traceTc (text "binding" <+> ppr name <+> ppr (idType id))
+ >> thing_inside)
+ ; let pat' | isEmptyLHsBinds binds = VarPat id
+ | otherwise = VarPatOut id binds
+ ; return (pat', [], res) }
+
+tc_pat ctxt (ParPat pat) pat_ty thing_inside
+ = do { (pat', tvs, res) <- tc_lpat ctxt pat pat_ty thing_inside
+ ; return (ParPat pat', tvs, res) }
+
+-- There's a wrinkle with irrefuatable 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
+tc_pat ctxt lpat@(LazyPat pat) pat_ty thing_inside
+ = do { reft <- getTypeRefinement
+ ; (pat', pat_tvs, res) <- tc_lpat ctxt pat pat_ty $
+ setTypeRefinement reft thing_inside
+ ; if (null pat_tvs) then return ()
+ else lazyPatErr lpat pat_tvs
+ ; return (LazyPat pat', [], res) }
+
+tc_pat ctxt (WildPat _) pat_ty thing_inside
+ = do { pat_ty' <- zapExpectedType pat_ty argTypeKind
+ -- Note argTypeKind, so that
+ -- f _ = 3
+ -- is rejected when f applied to an unboxed tuple
+ -- However, this means that
+ -- (case g x of _ -> ...)
+ -- is rejected g returns an unboxed tuple, which is perhpas
+ -- annoying. I suppose we could pass the context into tc_pat...
+ ; res <- thing_inside
+ ; return (WildPat pat_ty', [], res) }
+
+tc_pat ctxt (AsPat (L nm_loc name) pat) pat_ty thing_inside
+ = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr ctxt name pat_ty)
+ ; (pat', tvs, res) <- tcExtendIdEnv1 name bndr_id $
+ tc_lpat ctxt pat (Check (idType bndr_id)) 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
+ -- fails to unify with the polymorphic type for 'x'. This could
+ -- 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) }
+
+tc_pat ctxt (SigPatIn pat sig) pat_ty thing_inside
+ = do { -- See Note [Pattern coercions] below
+ (sig_tvs, sig_ty) <- tcHsPatSigType PatSigCtxt sig
+ ; tcSubPat sig_ty pat_ty
+ ; (pat', tvs, res) <- tcExtendTyVarEnv sig_tvs $
+ tc_lpat ctxt pat (Check sig_ty) thing_inside
+ ; return (SigPatOut pat' sig_ty, tvs, res) }
+
+tc_pat ctxt pat@(TypePat ty) pat_ty thing_inside
+ = failWithTc (badTypePat pat)
+
+------------------------
+-- Lists, tuples, arrays
+tc_pat ctxt (ListPat pats _) pat_ty thing_inside
+ = do { elem_ty <- zapToListTy pat_ty
+ ; (pats', pats_tvs, res) <- tcCheckPats ctxt pats (repeat elem_ty) thing_inside
+ ; return (ListPat pats' elem_ty, pats_tvs, res) }
+
+tc_pat ctxt (PArrPat pats _) pat_ty thing_inside
+ = do { [elem_ty] <- zapToTyConApp parrTyCon pat_ty
+ ; (pats', pats_tvs, res) <- tcCheckPats ctxt pats (repeat elem_ty) thing_inside
+ ; return (PArrPat pats' elem_ty, pats_tvs, res) }
+
+tc_pat ctxt (TuplePat pats boxity) pat_ty thing_inside
+ = do { let arity = length pats
+ tycon = tupleTyCon boxity arity
+ ; arg_tys <- zapToTyConApp tycon pat_ty
+ ; (pats', pats_tvs, res) <- tcCheckPats ctxt pats arg_tys thing_inside
- returnTc (ConOpPat pat1' con_id pat2' data_ty,
- lie1 `plusLIE` lie2,
- data_ty)
+ -- 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
+ possibly_mangled_result
+ | opt_IrrefutableTuples && isBoxed boxity = LazyPat (noLoc unmangled_result)
+ | otherwise = unmangled_result
+
+ ; ASSERT( length arg_tys == arity ) -- Syntactically enforced
+ return (possibly_mangled_result, pats_tvs, res) }
+
+------------------------
+-- Data constructors
+tc_pat ctxt 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
+ ; ty_args <- zapToTyConApp tycon pat_ty
+ ; (pat', tvs, res) <- tcConPat ctxt con_span data_con tycon ty_args arg_pats thing_inside
+ ; return (pat', tvs, res) }
+
+
+------------------------
+-- Literal patterns
+tc_pat ctxt pat@(LitPat lit@(HsString _)) pat_ty thing_inside
+ = do { -- Strings are mapped to NPatOuts, which have a guard expression
+ zapExpectedTo pat_ty stringTy
+ ; eq_id <- tcLookupId eqStringName
+ ; res <- thing_inside
+ ; returnM (NPatOut lit stringTy (nlHsVar eq_id `HsApp` nlHsLit lit), [], res) }
+
+tc_pat ctxt (LitPat simple_lit) pat_ty thing_inside
+ = do { -- All other simple lits
+ zapExpectedTo pat_ty (hsLitType simple_lit)
+ ; res <- thing_inside
+ ; returnM (LitPat simple_lit, [], res) }
+
+------------------------
+-- Overloaded patterns: n, and n+k
+tc_pat ctxt pat@(NPatIn over_lit mb_neg) pat_ty thing_inside
+ = do { pat_ty' <- zapExpectedType pat_ty liftedTypeKind
+ ; let origin = LiteralOrigin over_lit
+ ; pos_lit_expr <- newOverloadedLit origin over_lit pat_ty'
+ ; eq <- newMethodFromName origin pat_ty' eqName
+ ; lit_expr <- case mb_neg of
+ Nothing -> returnM pos_lit_expr -- Positive literal
+ Just neg -> -- Negative literal
+ -- The 'negate' is re-mappable syntax
+ do { (_, neg_expr) <- tcSyntaxName origin pat_ty'
+ (negateName, HsVar neg)
+ ; returnM (mkHsApp (noLoc neg_expr) pos_lit_expr) }
+
+ ; let -- The literal in an NPatIn is always positive...
+ -- But in NPatOut, the literal is used to find identical patterns
+ -- so we must negate the literal when necessary!
+ lit' = case (over_lit, mb_neg) of
+ (HsIntegral i _, Nothing) -> HsInteger i pat_ty'
+ (HsIntegral i _, Just _) -> HsInteger (-i) pat_ty'
+ (HsFractional f _, Nothing) -> HsRat f pat_ty'
+ (HsFractional f _, Just _) -> HsRat (-f) pat_ty'
+
+ ; res <- thing_inside
+ ; returnM (NPatOut lit' pat_ty' (HsApp (nlHsVar eq) lit_expr), [], res) }
+
+tc_pat ctxt pat@(NPlusKPatIn (L nm_loc name) lit@(HsIntegral i _) minus_name) pat_ty thing_inside
+ = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr ctxt name pat_ty)
+ ; let pat_ty' = idType bndr_id
+ origin = LiteralOrigin lit
+ ; over_lit_expr <- newOverloadedLit origin lit pat_ty'
+ ; ge <- newMethodFromName origin pat_ty' geName
+
+ -- The '-' part is re-mappable syntax
+ ; (_, minus_expr) <- tcSyntaxName origin pat_ty' (minusName, HsVar minus_name)
+
+ -- 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
+ ; dicts <- newDicts origin [mkClassPred icls [pat_ty']]
+ ; extendLIEs dicts
+
+ ; res <- tcExtendIdEnv1 name bndr_id thing_inside
+ ; returnM (NPlusKPatOut (L nm_loc bndr_id) i
+ (SectionR (nlHsVar ge) over_lit_expr)
+ (SectionR (noLoc minus_expr) over_lit_expr),
+ [], res) }
\end{code}
+
%************************************************************************
%* *
-\subsection{Records}
+ Most of the work for constructors is here
+ (the rest is in the ConPatIn case of tc_pat)
%* *
%************************************************************************
\begin{code}
-tcPat pat_in@(RecPatIn name rpats)
- = tcLookupGlobalValue name `thenNF_Tc` \ con_id ->
- tcInstId con_id `thenNF_Tc` \ (_, _, con_tau) ->
- let
- -- Ignore the con_theta; overloaded constructors only
- -- behave differently when called, not when used for
- -- matching.
- (_, record_ty) = splitFunTys con_tau
- in
- -- Con is syntactically constrained to be a data constructor
- ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty) )
-
- mapAndUnzipTc (do_bind record_ty) rpats `thenTc` \ (rpats', lies) ->
-
- returnTc (RecPat con_id record_ty rpats',
- plusLIEs lies,
- record_ty)
+tcConPat :: PatCtxt -> SrcSpan -> DataCon -> TyCon -> [TcTauType]
+ -> HsConDetails Name (LPat Name) -> TcM a
+ -> TcM (Pat TcId, [TcTyVar], a)
+tcConPat ctxt span data_con tycon ty_args arg_pats thing_inside
+ | isVanillaDataCon data_con
+ = do { let arg_tys = dataConInstOrigArgTys data_con ty_args
+ ; tcInstStupidTheta data_con ty_args
+ ; traceTc (text "tcConPat" <+> vcat [ppr data_con, ppr ty_args, ppr arg_tys])
+ ; (arg_pats', tvs, res) <- tcConArgs ctxt data_con arg_pats arg_tys thing_inside
+ ; return (ConPatOut (L span data_con) [] [] emptyLHsBinds
+ arg_pats' (mkTyConApp tycon ty_args),
+ tvs, res) }
+
+ | otherwise -- GADT case
+ = do { let (tvs, theta, arg_tys, _, res_tys) = dataConSig data_con
+ ; span <- getSrcSpanM
+ ; let rigid_info = PatSkol data_con span
+ ; tvs' <- tcSkolTyVars rigid_info tvs
+ ; let tv_tys' = mkTyVarTys tvs'
+ tenv = zipTopTvSubst tvs tv_tys'
+ theta' = substTheta tenv theta
+ arg_tys' = substTys tenv arg_tys
+ res_tys' = substTys tenv res_tys
+ ; dicts <- newDicts (SigOrigin rigid_info) theta'
+
+ -- Do type refinement!
+ ; traceTc (text "tcGadtPat" <+> vcat [ppr data_con, ppr tvs', ppr arg_tys', ppr res_tys',
+ text "ty-args:" <+> ppr ty_args ])
+ ; refineAlt ctxt data_con tvs' ty_args res_tys' $ do
+
+ { ((arg_pats', inner_tvs, res), lie_req) <- getLIE $
+ do { tcInstStupidTheta data_con tv_tys'
+ -- The stupid-theta mentions the newly-bound tyvars, so
+ -- it must live inside the getLIE, so that the
+ -- tcSimplifyCheck will apply the type refinement to it
+ ; tcConArgs ctxt data_con arg_pats arg_tys' thing_inside }
+
+ ; dict_binds <- tcSimplifyCheck doc tvs' dicts lie_req
+
+ ; return (ConPatOut (L span data_con)
+ tvs' (map instToId dicts) dict_binds
+ arg_pats' (mkTyConApp tycon ty_args),
+ tvs' ++ inner_tvs, res) } }
+ where
+ doc = ptext SLIT("existential context for") <+> quotes (ppr data_con)
+
+tcConArgs :: PatCtxt -> DataCon
+ -> HsConDetails Name (LPat Name) -> [TcSigmaType]
+ -> TcM a
+ -> TcM (HsConDetails TcId (LPat Id), [TcTyVar], a)
+
+tcConArgs ctxt data_con (PrefixCon arg_pats) arg_tys thing_inside
+ = do { checkTc (con_arity == no_of_args) -- Check correct arity
+ (arityErr "Constructor" data_con con_arity no_of_args)
+ ; (arg_pats', tvs, res) <- tcCheckPats ctxt arg_pats arg_tys thing_inside
+ ; return (PrefixCon arg_pats', tvs, res) }
+ where
+ con_arity = dataConSourceArity data_con
+ no_of_args = length arg_pats
+
+tcConArgs ctxt data_con (InfixCon p1 p2) arg_tys thing_inside
+ = do { checkTc (con_arity == 2) -- Check correct arity
+ (arityErr "Constructor" data_con con_arity 2)
+ ; ([p1',p2'], tvs, res) <- tcCheckPats ctxt [p1,p2] arg_tys thing_inside
+ ; return (InfixCon p1' p2', tvs, res) }
+ where
+ con_arity = dataConSourceArity data_con
+tcConArgs ctxt data_con (RecCon rpats) arg_tys thing_inside
+ = do { (rpats', tvs, res) <- tc_fields rpats thing_inside
+ ; return (RecCon rpats', tvs, res) }
where
- do_bind expected_record_ty (field_label, rhs_pat, pun_flag)
- = tcLookupGlobalValue field_label `thenNF_Tc` \ sel_id ->
- tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
-
- -- Record selectors all have type
- -- forall a1..an. T a1 .. an -> tau
- ASSERT( maybeToBool (splitFunTy_maybe tau) )
- let
- -- Selector must have type RecordType -> FieldType
- Just (record_ty, field_ty) = splitFunTy_maybe tau
- in
- tcAddErrCtxt (recordLabel field_label) (
- unifyTauTy expected_record_ty record_ty
- ) `thenTc_`
- tcPat rhs_pat `thenTc` \ (rhs_pat', lie, rhs_ty) ->
- tcAddErrCtxt (recordRhs field_label rhs_pat) (
- unifyTauTy field_ty rhs_ty
- ) `thenTc_`
- returnTc ((sel_id, rhs_pat', pun_flag), lie)
+ tc_fields :: [(Located Name, LPat Name)] -> TcM a
+ -> TcM ([(Located TcId, LPat TcId)], [TcTyVar], a)
+ tc_fields [] thing_inside
+ = do { res <- thing_inside
+ ; return ([], [], res) }
+
+ tc_fields (rpat : rpats) thing_inside
+ = do { (rpat', tvs1, (rpats', tvs2, res))
+ <- tc_field rpat (tc_fields rpats thing_inside)
+ ; return (rpat':rpats', tvs1 ++ tvs2, res) }
+
+ tc_field (field_lbl, pat) thing_inside
+ = do { (sel_id, pat_ty) <- wrapLocFstM find_field_ty field_lbl
+ ; (pat', tvs, res) <- tcPat ctxt pat (Check pat_ty) thing_inside
+ ; return ((sel_id, pat'), tvs, res) }
+
+ find_field_ty field_lbl
+ = case [ty | (f,ty) <- field_tys, f == field_lbl] of
+
+ -- No matching field; chances are this field label comes from some
+ -- other record type (or maybe none). As well as reporting an
+ -- error we still want to typecheck the pattern, principally to
+ -- make sure that all the variables it binds are put into the
+ -- environment, else the type checker crashes later:
+ -- f (R { foo = (a,b) }) = a+b
+ -- If foo isn't one of R's fields, we don't want to crash when
+ -- typechecking the "a+b".
+ [] -> do { addErrTc (badFieldCon data_con field_lbl)
+ ; bogus_ty <- newTyFlexiVarTy liftedTypeKind
+ ; return (error "Bogus selector Id", bogus_ty) }
+
+ -- The normal case, when the field comes from the right constructor
+ (pat_ty : extras) ->
+ ASSERT( null extras )
+ do { sel_id <- tcLookupId field_lbl
+ ; return (sel_id, pat_ty) }
+
+ field_tys = zip (dataConFieldLabels data_con) arg_tys
+ -- Don't use zipEqual! If the constructor isn't really a record, then
+ -- dataConFieldLabels will be empty (and each field in the pattern
+ -- will generate an error below).
\end{code}
+
%************************************************************************
%* *
-\subsection{Non-overloaded literals}
+ Type refinement
%* *
%************************************************************************
\begin{code}
-tcPat (LitPatIn lit@(HsChar str))
- = returnTc (LitPat lit charTy, emptyLIE, charTy)
-
-tcPat (LitPatIn lit@(HsString str))
- = tcLookupGlobalValueByKey eqClassOpKey `thenNF_Tc` \ sel_id ->
- newMethod (LiteralOrigin lit)
- (RealId sel_id) [stringTy] `thenNF_Tc` \ (lie, eq_id) ->
- let
- comp_op = HsApp (HsVar eq_id) (HsLitOut lit stringTy)
- in
- returnTc (NPat lit stringTy comp_op, lie, stringTy)
-
-tcPat (LitPatIn lit@(HsIntPrim _))
- = returnTc (LitPat lit intPrimTy, emptyLIE, intPrimTy)
-tcPat (LitPatIn lit@(HsCharPrim _))
- = returnTc (LitPat lit charPrimTy, emptyLIE, charPrimTy)
-tcPat (LitPatIn lit@(HsStringPrim _))
- = returnTc (LitPat lit addrPrimTy, emptyLIE, addrPrimTy)
-tcPat (LitPatIn lit@(HsFloatPrim _))
- = returnTc (LitPat lit floatPrimTy, emptyLIE, floatPrimTy)
-tcPat (LitPatIn lit@(HsDoublePrim _))
- = returnTc (LitPat lit doublePrimTy, emptyLIE, doublePrimTy)
+refineAlt :: PatCtxt -> DataCon
+ -> [TcTyVar] -- Freshly bound type variables
+ -> [TcType] -- Types from the scrutinee (context)
+ -> [TcType] -- Types from the pattern
+ -> TcM a -> TcM a
+refineAlt ctxt con ex_tvs ctxt_tys pat_tys thing_inside
+ = do { old_subst <- getTypeRefinement
+ ; let refiner | can_i_refine ctxt = tcRefineTys
+ | otherwise = tcMatchTys
+ ; case refiner ex_tvs old_subst pat_tys ctxt_tys of
+ Failed msg -> failWithTc (inaccessibleAlt msg)
+ Succeeded new_subst -> do {
+ traceTc (text "refineTypes:match" <+> ppr con <+> ppr new_subst)
+ ; setTypeRefinement new_subst thing_inside } }
+
+ where
+ can_i_refine (LamPat can_refine) = can_refine
+ can_i_refine other_ctxt = False
\end{code}
%************************************************************************
%* *
-\subsection{Overloaded patterns: int literals and \tr{n+k} patterns}
+ Note [Pattern coercions]
%* *
%************************************************************************
-\begin{code}
-tcPat (LitPatIn lit@(HsInt i))
- = newTyVarTy mkBoxedTypeKind `thenNF_Tc` \ tyvar_ty ->
- newOverloadedLit origin
- (OverloadedIntegral i) tyvar_ty `thenNF_Tc` \ (over_lit_expr, lie1) ->
-
- tcLookupGlobalValueByKey eqClassOpKey `thenNF_Tc` \ eq_sel_id ->
- newMethod origin (RealId eq_sel_id) [tyvar_ty] `thenNF_Tc` \ (lie2, eq_id) ->
-
- returnTc (NPat lit tyvar_ty (HsApp (HsVar eq_id)
- over_lit_expr),
- lie1 `plusLIE` lie2,
- tyvar_ty)
- where
- origin = LiteralOrigin lit
+In principle, these program would be reasonable:
+
+ f :: (forall a. a->a) -> Int
+ f (x :: Int->Int) = x 3
-tcPat (LitPatIn lit@(HsFrac f))
- = newTyVarTy mkBoxedTypeKind `thenNF_Tc` \ tyvar_ty ->
- newOverloadedLit origin
- (OverloadedFractional f) tyvar_ty `thenNF_Tc` \ (over_lit_expr, lie1) ->
+ g :: (forall a. [a]) -> Bool
+ g [] = True
- tcLookupGlobalValueByKey eqClassOpKey `thenNF_Tc` \ eq_sel_id ->
- newMethod origin (RealId eq_sel_id) [tyvar_ty] `thenNF_Tc` \ (lie2, eq_id) ->
+In both cases, the function type signature restricts what arguments can be passed
+in a call (to polymorphic ones). The pattern type signature then instantiates this
+type. For example, in the first case, (forall a. a->a) <= Int -> Int, and we
+generate the translated term
+ f = \x' :: (forall a. a->a). let x = x' Int in x 3
- returnTc (NPat lit tyvar_ty (HsApp (HsVar eq_id)
- over_lit_expr),
- lie1 `plusLIE` lie2,
- tyvar_ty)
- where
- origin = LiteralOrigin lit
-
-tcPat (LitPatIn lit@(HsLitLit s))
--- = error "tcPat: can't handle ``literal-literal'' patterns"
- = returnTc (LitPat lit intTy, emptyLIE, intTy)
-
-tcPat (NPlusKPatIn name lit@(HsInt i))
- = tcLookupLocalValueOK "tcPat1:n+k" name `thenNF_Tc` \ local ->
- let
- local_ty = idType local
- in
- tcLookupGlobalValueByKey geClassOpKey `thenNF_Tc` \ ge_sel_id ->
- tcLookupGlobalValueByKey minusClassOpKey `thenNF_Tc` \ minus_sel_id ->
-
- newOverloadedLit origin
- (OverloadedIntegral i) local_ty `thenNF_Tc` \ (over_lit_expr, lie1) ->
-
- newMethod origin (RealId ge_sel_id) [local_ty] `thenNF_Tc` \ (lie2, ge_id) ->
- newMethod origin (RealId minus_sel_id) [local_ty] `thenNF_Tc` \ (lie3, minus_id) ->
-
- returnTc (NPlusKPat (TcId local) lit local_ty
- (SectionR (HsVar ge_id) over_lit_expr)
- (SectionR (HsVar minus_id) over_lit_expr),
- lie1 `plusLIE` lie2 `plusLIE` lie3,
- local_ty)
- where
- origin = LiteralOrigin lit -- Not very good!
+From a type-system point of view, this is perfectly fine, but it's *very* seldom useful.
+And it requires a significant amount of code to implement, becuase we need to decorate
+the translated pattern with coercion functions (generated from the subsumption check
+by tcSub).
-tcPat (NPlusKPatIn pat other) = panic "TcPat:NPlusKPat: not an HsInt literal"
-\end{code}
+So for now I'm just insisting on type *equality* in patterns. No subsumption.
-%************************************************************************
-%* *
-\subsection{Lists of patterns}
-%* *
-%************************************************************************
+Old notes about desugaring, at a time when pattern coercions were handled:
-\begin{code}
-tcPats :: [RenamedPat] -> TcM s ([TcPat s], LIE s, [TcType s])
+A SigPat is a type coercion and must be handled one at at time. We can't
+combine them unless the type of the pattern inside is identical, and we don't
+bother to check for that. For example:
-tcPats [] = returnTc ([], emptyLIE, [])
+ data T = T1 Int | T2 Bool
+ f :: (forall a. a -> a) -> T -> t
+ f (g::Int->Int) (T1 i) = T1 (g i)
+ f (g::Bool->Bool) (T2 b) = T2 (g b)
-tcPats (pat:pats)
- = tcPat pat `thenTc` \ (pat', lie, ty) ->
- tcPats pats `thenTc` \ (pats', lie', tys) ->
+We desugar this as follows:
- returnTc (pat':pats', plusLIE lie lie', ty:tys)
-\end{code}
+ f = \ g::(forall a. a->a) t::T ->
+ let gi = g Int
+ in case t of { T1 i -> T1 (gi i)
+ other ->
+ let gb = g Bool
+ in case t of { T2 b -> T2 (gb b)
+ other -> fail }}
-@matchConArgTys@ grabs the signature of the data constructor, and
-unifies the actual args against the expected ones.
+Note that we do not treat the first column of patterns as a
+column of variables, because the coerced variables (gi, gb)
+would be of different types. So we get rather grotty code.
+But I don't think this is a common case, and if it was we could
+doubtless improve it.
-\begin{code}
-matchConArgTys :: Name -> [TcType s] -> TcM s (Id, TcType s)
-
-matchConArgTys con arg_tys
- = tcLookupGlobalValue con `thenNF_Tc` \ con_id ->
- tcInstId con_id `thenNF_Tc` \ (_, _, con_tau) ->
- -- Ignore the con_theta; overloaded constructors only
- -- behave differently when called, not when used for
- -- matching.
- let
- (con_args, con_result) = splitFunTys con_tau
- con_arity = length con_args
- no_of_args = length arg_tys
- in
- checkTc (con_arity == no_of_args)
- (arityErr "Constructor" con_id con_arity no_of_args) `thenTc_`
-
- unifyTauTyLists con_args arg_tys `thenTc_`
- returnTc (con_id, con_result)
-\end{code}
+Meanwhile, the strategy is:
+ * treat each SigPat coercion (always non-identity coercions)
+ as a separate block
+ * deal with the stuff inside, and then wrap a binding round
+ the result to bind the new variable (gi, gb, etc)
-% =================================================
+%************************************************************************
+%* *
+\subsection{Errors and contexts}
+%* *
+%************************************************************************
-Errors and contexts
-~~~~~~~~~~~~~~~~~~~
\begin{code}
-patCtxt pat = hang (ptext SLIT("In the pattern:"))
- 4 (ppr pat)
-
-recordLabel field_label
- = hang (hcat [ptext SLIT("When matching record field"), ppr field_label])
- 4 (hcat [ptext SLIT("with its immediately enclosing constructor")])
+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("When checking the pattern:"))
+ 4 (ppr pat))
+
+badFieldCon :: DataCon -> Name -> SDoc
+badFieldCon con 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)
+
+badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
+
+lazyPatErr pat tvs
+ = failWithTc $
+ hang (ptext SLIT("A lazy (~) pattern connot bind existential type variables"))
+ 2 (vcat (map get tvs))
+ where
+ get tv = ASSERT( isSkolemTyVar tv ) pprSkolemTyVar tv
-recordRhs field_label pat
- = hang (ptext SLIT("In the record field pattern"))
- 4 (sep [ppr field_label, char '=', ppr pat])
+inaccessibleAlt msg
+ = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg
\end{code}