+++ /dev/null
-%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
-%
-\section[TcMatches]{Typecheck some @Matches@}
-
-\begin{code}
-module TcMatches ( tcMatchesFun, tcGRHSsPat, tcMatchesCase, tcMatchLambda,
- matchCtxt, TcMatchCtxt(..),
- tcStmts, tcDoStmts,
- tcDoStmt, tcMDoStmt, tcGuardStmt
- ) where
-
-#include "HsVersions.h"
-
-import {-# SOURCE #-} TcExpr( tcSyntaxOp, tcInferRho, tcMonoExpr, tcPolyExpr )
-
-import HsSyn ( HsExpr(..), LHsExpr, MatchGroup(..),
- Match(..), LMatch, GRHSs(..), GRHS(..),
- Stmt(..), LStmt, HsMatchContext(..), HsStmtContext(..),
- pprMatch, isIrrefutableHsPat, mkHsCoerce,
- pprMatchContext, pprStmtContext,
- noSyntaxExpr, matchGroupArity, pprMatches,
- ExprCoFn )
-
-import TcRnMonad
-import TcHsType ( tcPatSig, UserTypeCtxt(..) )
-import Inst ( newMethodFromName )
-import TcEnv ( TcId, tcLookupLocalIds, tcLookupId, tcExtendIdEnv,
- tcExtendTyVarEnv2 )
-import TcPat ( PatCtxt(..), tcPats, tcPat )
-import TcMType ( newFlexiTyVarTy, newFlexiTyVarTys )
-import TcType ( TcType, TcRhoType,
- BoxySigmaType, BoxyRhoType,
- mkFunTys, mkFunTy, mkAppTy, mkTyConApp,
- liftedTypeKind )
-import TcBinds ( tcLocalBinds )
-import TcUnify ( boxySplitAppTy, boxySplitTyConApp, boxySplitListTy,
- subFunTys, tcSubExp, withBox )
-import TcSimplify ( bindInstsOfLocalFuns )
-import Name ( Name )
-import TysWiredIn ( stringTy, boolTy, parrTyCon, listTyCon, mkListTy, mkPArrTy )
-import PrelNames ( bindMName, returnMName, mfixName, thenMName, failMName )
-import Id ( idType, mkLocalId )
-import TyCon ( TyCon )
-import Outputable
-import SrcLoc ( Located(..), getLoc )
-import ErrUtils ( Message )
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{tcMatchesFun, tcMatchesCase}
-%* *
-%************************************************************************
-
-@tcMatchesFun@ typechecks a @[Match]@ list which occurs in a
-@FunMonoBind@. The second argument is the name of the function, which
-is used in error messages. It checks that all the equations have the
-same number of arguments before using @tcMatches@ to do the work.
-
-\begin{code}
-tcMatchesFun :: Name
- -> MatchGroup Name
- -> BoxyRhoType -- Expected type of function
- -> TcM (ExprCoFn, MatchGroup TcId) -- Returns type of body
-
-tcMatchesFun fun_name matches exp_ty
- = do { -- Check that they all have the same no of arguments
- -- Location is in the monad, set the caller so that
- -- any inter-equation error messages get some vaguely
- -- sensible location. Note: we have to do this odd
- -- ann-grabbing, because we don't always have annotations in
- -- hand when we call tcMatchesFun...
- checkArgs fun_name matches
-
- -- ToDo: Don't use "expected" stuff if there ain't a type signature
- -- because inconsistency between branches
- -- may show up as something wrong with the (non-existent) type signature
-
- -- This is one of two places places we call subFunTys
- -- The point is that if expected_y is a "hole", we want
- -- to make pat_tys and rhs_ty as "holes" too.
- ; subFunTys doc n_pats exp_ty $ \ pat_tys rhs_ty ->
- tcMatches match_ctxt pat_tys rhs_ty matches
- }
- where
- doc = ptext SLIT("The equation(s) for") <+> quotes (ppr fun_name)
- <+> ptext SLIT("have") <+> speakNOf n_pats (ptext SLIT("argument"))
- n_pats = matchGroupArity matches
- match_ctxt = MC { mc_what = FunRhs fun_name, mc_body = tcPolyExpr }
-\end{code}
-
-@tcMatchesCase@ doesn't do the argument-count check because the
-parser guarantees that each equation has exactly one argument.
-
-\begin{code}
-tcMatchesCase :: TcMatchCtxt -- Case context
- -> TcRhoType -- Type of scrutinee
- -> MatchGroup Name -- The case alternatives
- -> BoxyRhoType -- Type of whole case expressions
- -> TcM (MatchGroup TcId) -- Translated alternatives
-
-tcMatchesCase ctxt scrut_ty matches res_ty
- = tcMatches ctxt [scrut_ty] res_ty matches
-
-tcMatchLambda :: MatchGroup Name -> BoxyRhoType -> TcM (ExprCoFn, MatchGroup TcId)
-tcMatchLambda match res_ty
- = subFunTys doc n_pats res_ty $ \ pat_tys rhs_ty ->
- tcMatches match_ctxt pat_tys rhs_ty match
- where
- n_pats = matchGroupArity match
- doc = sep [ ptext SLIT("The lambda expression")
- <+> quotes (pprSetDepth 1 $ pprMatches LambdaExpr match),
- -- The pprSetDepth makes the abstraction print briefly
- ptext SLIT("has") <+> speakNOf n_pats (ptext SLIT("argument"))]
- match_ctxt = MC { mc_what = LambdaExpr,
- mc_body = tcPolyExpr }
-\end{code}
-
-@tcGRHSsPat@ typechecks @[GRHSs]@ that occur in a @PatMonoBind@.
-
-\begin{code}
-tcGRHSsPat :: GRHSs Name -> BoxyRhoType -> TcM (GRHSs TcId)
-tcGRHSsPat grhss res_ty = tcGRHSs match_ctxt grhss res_ty
- where
- match_ctxt = MC { mc_what = PatBindRhs,
- mc_body = tcPolyExpr }
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{tcMatch}
-%* *
-%************************************************************************
-
-\begin{code}
-tcMatches :: TcMatchCtxt
- -> [BoxySigmaType] -- Expected pattern types
- -> BoxyRhoType -- Expected result-type of the Match.
- -> MatchGroup Name
- -> TcM (MatchGroup TcId)
-
-data TcMatchCtxt -- c.f. TcStmtCtxt, also in this module
- = MC { mc_what :: HsMatchContext Name, -- What kind of thing this is
- mc_body :: LHsExpr Name -- Type checker for a body of an alternative
- -> BoxyRhoType
- -> TcM (LHsExpr TcId) }
-
-tcMatches ctxt pat_tys rhs_ty (MatchGroup matches _)
- = do { matches' <- mapM (tcMatch ctxt pat_tys rhs_ty) matches
- ; return (MatchGroup matches' (mkFunTys pat_tys rhs_ty)) }
-
--------------
-tcMatch :: TcMatchCtxt
- -> [BoxySigmaType] -- Expected pattern types
- -> BoxyRhoType -- Expected result-type of the Match.
- -> LMatch Name
- -> TcM (LMatch TcId)
-
-tcMatch ctxt pat_tys rhs_ty match
- = wrapLocM (tc_match ctxt pat_tys rhs_ty) match
- where
- tc_match ctxt pat_tys rhs_ty match@(Match pats maybe_rhs_sig grhss)
- = addErrCtxt (matchCtxt (mc_what ctxt) match) $
- do { (pats', grhss') <- tcPats LamPat pats pat_tys rhs_ty $
- tc_grhss ctxt maybe_rhs_sig grhss
- ; returnM (Match pats' Nothing grhss') }
-
- tc_grhss ctxt Nothing grhss rhs_ty
- = tcGRHSs ctxt grhss rhs_ty -- No result signature
-
- tc_grhss ctxt (Just res_sig) grhss rhs_ty
- = do { (inner_ty, sig_tvs) <- tcPatSig ResSigCtxt res_sig rhs_ty
- ; tcExtendTyVarEnv2 sig_tvs $
- tcGRHSs ctxt grhss inner_ty }
-
--------------
-tcGRHSs :: TcMatchCtxt -> GRHSs Name -> BoxyRhoType -> TcM (GRHSs TcId)
-
--- Notice that we pass in the full res_ty, so that we get
--- good inference from simple things like
--- f = \(x::forall a.a->a) -> <stuff>
--- We used to force it to be a monotype when there was more than one guard
--- but we don't need to do that any more
-
-tcGRHSs ctxt (GRHSs grhss binds) res_ty
- = do { (binds', grhss') <- tcLocalBinds binds $
- mappM (wrapLocM (tcGRHS ctxt res_ty)) grhss
-
- ; returnM (GRHSs grhss' binds') }
-
--------------
-tcGRHS :: TcMatchCtxt -> BoxyRhoType -> GRHS Name -> TcM (GRHS TcId)
-
-tcGRHS ctxt res_ty (GRHS guards rhs)
- = do { (guards', rhs') <- tcStmts stmt_ctxt tcGuardStmt guards res_ty $
- mc_body ctxt rhs
- ; return (GRHS guards' rhs') }
- where
- stmt_ctxt = PatGuard (mc_what ctxt)
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
-%* *
-%************************************************************************
-
-\begin{code}
-tcDoStmts :: HsStmtContext Name
- -> [LStmt Name]
- -> LHsExpr Name
- -> BoxyRhoType
- -> TcM (HsExpr TcId) -- Returns a HsDo
-tcDoStmts ListComp stmts body res_ty
- = do { elt_ty <- boxySplitListTy res_ty
- ; (stmts', body') <- tcStmts ListComp (tcLcStmt listTyCon) stmts elt_ty $
- tcBody (doBodyCtxt ListComp body) body
- ; return (HsDo ListComp stmts' body' (mkListTy elt_ty)) }
-
-tcDoStmts PArrComp stmts body res_ty
- = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
- ; (stmts', body') <- tcStmts PArrComp (tcLcStmt parrTyCon) stmts elt_ty $
- tcBody (doBodyCtxt PArrComp body) body
- ; return (HsDo PArrComp stmts' body' (mkPArrTy elt_ty)) }
-
-tcDoStmts DoExpr stmts body res_ty
- = do { (m_ty, elt_ty) <- boxySplitAppTy res_ty
- ; let res_ty' = mkAppTy m_ty elt_ty -- The boxySplit consumes res_ty
- ; (stmts', body') <- tcStmts DoExpr (tcDoStmt m_ty) stmts res_ty' $
- tcBody (doBodyCtxt DoExpr body) body
- ; return (HsDo DoExpr stmts' body' res_ty') }
-
-tcDoStmts ctxt@(MDoExpr _) stmts body res_ty
- = do { (m_ty, elt_ty) <- boxySplitAppTy res_ty
- ; let res_ty' = mkAppTy m_ty elt_ty -- The boxySplit consumes res_ty
- tc_rhs rhs = withBox liftedTypeKind $ \ pat_ty ->
- tcMonoExpr rhs (mkAppTy m_ty pat_ty)
-
- ; (stmts', body') <- tcStmts ctxt (tcMDoStmt tc_rhs) stmts res_ty' $
- tcBody (doBodyCtxt ctxt body) body
-
- ; let names = [mfixName, bindMName, thenMName, returnMName, failMName]
- ; insts <- mapM (newMethodFromName DoOrigin m_ty) names
- ; return (HsDo (MDoExpr (names `zip` insts)) stmts' body' res_ty') }
-
-tcDoStmts ctxt stmts body res_ty = pprPanic "tcDoStmts" (pprStmtContext ctxt)
-
-tcBody :: Message -> LHsExpr Name -> BoxyRhoType -> TcM (LHsExpr TcId)
-tcBody ctxt body res_ty
- = -- addErrCtxt ctxt $ -- This context adds little that is useful
- tcPolyExpr body res_ty
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{tcStmts}
-%* *
-%************************************************************************
-
-\begin{code}
-type TcStmtChecker
- = forall thing. HsStmtContext Name
- -> Stmt Name
- -> BoxyRhoType -- Result type for comprehension
- -> (BoxyRhoType -> TcM thing) -- Checker for what follows the stmt
- -> TcM (Stmt TcId, thing)
-
- -- The incoming BoxyRhoType may be refined by type refinements
- -- before being passed to the thing_inside
-
-tcStmts :: HsStmtContext Name
- -> TcStmtChecker -- NB: higher-rank type
- -> [LStmt Name]
- -> BoxyRhoType
- -> (BoxyRhoType -> TcM thing)
- -> TcM ([LStmt TcId], thing)
-
--- Note the higher-rank type. stmt_chk is applied at different
--- types in the equations for tcStmts
-
-tcStmts ctxt stmt_chk [] res_ty thing_inside
- = do { thing <- thing_inside res_ty
- ; return ([], thing) }
-
--- LetStmts are handled uniformly, regardless of context
-tcStmts ctxt stmt_chk (L loc (LetStmt binds) : stmts) res_ty thing_inside
- = do { (binds', (stmts',thing)) <- tcLocalBinds binds $
- tcStmts ctxt stmt_chk stmts res_ty thing_inside
- ; return (L loc (LetStmt binds') : stmts', thing) }
-
--- For the vanilla case, handle the location-setting part
-tcStmts ctxt stmt_chk (L loc stmt : stmts) res_ty thing_inside
- = do { (stmt', (stmts', thing)) <-
- setSrcSpan loc $
- addErrCtxt (stmtCtxt ctxt stmt) $
- stmt_chk ctxt stmt res_ty $ \ res_ty' ->
- popErrCtxt $
- tcStmts ctxt stmt_chk stmts res_ty' $
- thing_inside
- ; return (L loc stmt' : stmts', thing) }
-
---------------------------------
--- Pattern guards
-tcGuardStmt :: TcStmtChecker
-tcGuardStmt ctxt (ExprStmt guard _ _) res_ty thing_inside
- = do { guard' <- tcMonoExpr guard boolTy
- ; thing <- thing_inside res_ty
- ; return (ExprStmt guard' noSyntaxExpr boolTy, thing) }
-
-tcGuardStmt ctxt (BindStmt pat rhs _ _) res_ty thing_inside
- = do { (rhs', rhs_ty) <- tcInferRho rhs
- ; (pat', thing) <- tcPat LamPat pat rhs_ty res_ty thing_inside
- ; return (BindStmt pat' rhs' noSyntaxExpr noSyntaxExpr, thing) }
-
-tcGuardStmt ctxt stmt res_ty thing_inside
- = pprPanic "tcGuardStmt: unexpected Stmt" (ppr stmt)
-
-
---------------------------------
--- List comprehensions and PArrays
-
-tcLcStmt :: TyCon -- The list/Parray type constructor ([] or PArray)
- -> TcStmtChecker
-
--- A generator, pat <- rhs
-tcLcStmt m_tc ctxt (BindStmt pat rhs _ _) res_ty thing_inside
- = do { (rhs', pat_ty) <- withBox liftedTypeKind $ \ ty ->
- tcMonoExpr rhs (mkTyConApp m_tc [ty])
- ; (pat', thing) <- tcPat LamPat pat pat_ty res_ty thing_inside
- ; return (BindStmt pat' rhs' noSyntaxExpr noSyntaxExpr, thing) }
-
--- A boolean guard
-tcLcStmt m_tc ctxt (ExprStmt rhs _ _) res_ty thing_inside
- = do { rhs' <- tcMonoExpr rhs boolTy
- ; thing <- thing_inside res_ty
- ; return (ExprStmt rhs' noSyntaxExpr boolTy, thing) }
-
--- A parallel set of comprehensions
--- [ (g x, h x) | ... ; let g v = ...
--- | ... ; let h v = ... ]
---
--- It's possible that g,h are overloaded, so we need to feed the LIE from the
--- (g x, h x) up through both lots of bindings (so we get the bindInstsOfLocalFuns).
--- Similarly if we had an existential pattern match:
---
--- data T = forall a. Show a => C a
---
--- [ (show x, show y) | ... ; C x <- ...
--- | ... ; C y <- ... ]
---
--- Then we need the LIE from (show x, show y) to be simplified against
--- the bindings for x and y.
---
--- It's difficult to do this in parallel, so we rely on the renamer to
--- ensure that g,h and x,y don't duplicate, and simply grow the environment.
--- So the binders of the first parallel group will be in scope in the second
--- group. But that's fine; there's no shadowing to worry about.
-
-tcLcStmt m_tc ctxt (ParStmt bndr_stmts_s) elt_ty thing_inside
- = do { (pairs', thing) <- loop bndr_stmts_s
- ; return (ParStmt pairs', thing) }
- where
- -- loop :: [([LStmt Name], [Name])] -> TcM ([([LStmt TcId], [TcId])], thing)
- loop [] = do { thing <- thing_inside elt_ty -- No refinement from pattern
- ; return ([], thing) } -- matching in the branches
-
- loop ((stmts, names) : pairs)
- = do { (stmts', (ids, pairs', thing))
- <- tcStmts ctxt (tcLcStmt m_tc) stmts elt_ty $ \ elt_ty' ->
- do { ids <- tcLookupLocalIds names
- ; (pairs', thing) <- loop pairs
- ; return (ids, pairs', thing) }
- ; return ( (stmts', ids) : pairs', thing ) }
-
-tcLcStmt m_tc ctxt stmt elt_ty thing_inside
- = pprPanic "tcLcStmt: unexpected Stmt" (ppr stmt)
-
---------------------------------
--- Do-notation
--- The main excitement here is dealing with rebindable syntax
-
-tcDoStmt :: TcType -- Monad type, m
- -> TcStmtChecker
-
-tcDoStmt m_ty ctxt (BindStmt pat rhs bind_op fail_op) res_ty thing_inside
- = do { (rhs', pat_ty) <- withBox liftedTypeKind $ \ pat_ty ->
- tcMonoExpr rhs (mkAppTy m_ty pat_ty)
- -- We should use type *inference* for the RHS computations, becuase of GADTs.
- -- do { pat <- rhs; <rest> }
- -- is rather like
- -- case rhs of { pat -> <rest> }
- -- We do inference on rhs, so that information about its type can be refined
- -- when type-checking the pattern.
-
- ; (pat', thing) <- tcPat LamPat pat pat_ty res_ty thing_inside
-
- -- Deal with rebindable syntax; (>>=) :: m a -> (a -> m b) -> m b
- ; let bind_ty = mkFunTys [mkAppTy m_ty pat_ty,
- mkFunTy pat_ty res_ty] res_ty
- ; bind_op' <- tcSyntaxOp DoOrigin bind_op bind_ty
- -- If (but only if) the pattern can fail,
- -- typecheck the 'fail' operator
- ; fail_op' <- if isIrrefutableHsPat pat'
- then return noSyntaxExpr
- else tcSyntaxOp DoOrigin fail_op (mkFunTy stringTy res_ty)
- ; return (BindStmt pat' rhs' bind_op' fail_op', thing) }
-
-
-tcDoStmt m_ty ctxt (ExprStmt rhs then_op _) res_ty thing_inside
- = do { -- Deal with rebindable syntax; (>>) :: m a -> m b -> m b
- a_ty <- newFlexiTyVarTy liftedTypeKind
- ; let rhs_ty = mkAppTy m_ty a_ty
- then_ty = mkFunTys [rhs_ty, res_ty] res_ty
- ; then_op' <- tcSyntaxOp DoOrigin then_op then_ty
- ; rhs' <- tcPolyExpr rhs rhs_ty
- ; thing <- thing_inside res_ty
- ; return (ExprStmt rhs' then_op' rhs_ty, thing) }
-
-tcDoStmt m_ty ctxt stmt res_ty thing_inside
- = pprPanic "tcDoStmt: unexpected Stmt" (ppr stmt)
-
---------------------------------
--- Mdo-notation
--- The distinctive features here are
--- (a) RecStmts, and
--- (b) no rebindable syntax
-
-tcMDoStmt :: (LHsExpr Name -> TcM (LHsExpr TcId, TcType)) -- RHS inference
- -> TcStmtChecker
-tcMDoStmt tc_rhs ctxt (BindStmt pat rhs bind_op fail_op) res_ty thing_inside
- = do { (rhs', pat_ty) <- tc_rhs rhs
- ; (pat', thing) <- tcPat LamPat pat pat_ty res_ty thing_inside
- ; return (BindStmt pat' rhs' noSyntaxExpr noSyntaxExpr, thing) }
-
-tcMDoStmt tc_rhs ctxt (ExprStmt rhs then_op _) res_ty thing_inside
- = do { (rhs', elt_ty) <- tc_rhs rhs
- ; thing <- thing_inside res_ty
- ; return (ExprStmt rhs' noSyntaxExpr elt_ty, thing) }
-
-tcMDoStmt tc_rhs ctxt (RecStmt stmts laterNames recNames _ _) res_ty thing_inside
- = do { rec_tys <- newFlexiTyVarTys (length recNames) liftedTypeKind
- ; let rec_ids = zipWith mkLocalId recNames rec_tys
- ; tcExtendIdEnv rec_ids $ do
- { (stmts', (later_ids, rec_rets))
- <- tcStmts ctxt (tcMDoStmt tc_rhs) stmts res_ty $ \ res_ty' ->
- -- ToDo: res_ty not really right
- do { rec_rets <- zipWithM tc_ret recNames rec_tys
- ; later_ids <- tcLookupLocalIds laterNames
- ; return (later_ids, rec_rets) }
-
- ; (thing,lie) <- tcExtendIdEnv later_ids (getLIE (thing_inside res_ty))
- -- NB: The rec_ids for the recursive things
- -- already scope over this part. This binding may shadow
- -- some of them with polymorphic things with the same Name
- -- (see note [RecStmt] in HsExpr)
- ; lie_binds <- bindInstsOfLocalFuns lie later_ids
-
- ; return (RecStmt stmts' later_ids rec_ids rec_rets lie_binds, thing)
- }}
- where
- -- Unify the types of the "final" Ids with those of "knot-tied" Ids
- tc_ret rec_name mono_ty
- = do { poly_id <- tcLookupId rec_name
- -- poly_id may have a polymorphic type
- -- but mono_ty is just a monomorphic type variable
- ; co_fn <- tcSubExp (idType poly_id) mono_ty
- ; return (mkHsCoerce co_fn (HsVar poly_id)) }
-
-tcMDoStmt tc_rhs ctxt stmt res_ty thing_inside
- = pprPanic "tcMDoStmt: unexpected Stmt" (ppr stmt)
-
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{Errors and contexts}
-%* *
-%************************************************************************
-
-@sameNoOfArgs@ takes a @[RenamedMatch]@ and decides whether the same
-number of args are used in each equation.
-
-\begin{code}
-checkArgs :: Name -> MatchGroup Name -> TcM ()
-checkArgs fun (MatchGroup (match1:matches) _)
- | null bad_matches = return ()
- | otherwise
- = failWithTc (vcat [ptext SLIT("Equations for") <+> quotes (ppr fun) <+>
- ptext SLIT("have different numbers of arguments"),
- nest 2 (ppr (getLoc match1)),
- nest 2 (ppr (getLoc (head bad_matches)))])
- where
- n_args1 = args_in_match match1
- bad_matches = [m | m <- matches, args_in_match m /= n_args1]
-
- args_in_match :: LMatch Name -> Int
- args_in_match (L _ (Match pats _ _)) = length pats
-\end{code}
-
-\begin{code}
-matchCtxt ctxt match = hang (ptext SLIT("In") <+> pprMatchContext ctxt <> colon)
- 4 (pprMatch ctxt match)
-
-doBodyCtxt :: HsStmtContext Name -> LHsExpr Name -> SDoc
-doBodyCtxt ctxt body = hang (ptext SLIT("In the result of") <+> pprStmtContext ctxt <> colon)
- 4 (ppr body)
-
-stmtCtxt ctxt stmt = hang (ptext SLIT("In") <+> pprStmtContext ctxt <> colon)
- 4 (ppr stmt)
-\end{code}
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