2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 Typecheck arrow notation
9 -- The above warning supression flag is a temporary kludge.
10 -- While working on this module you are encouraged to remove it and fix
11 -- any warnings in the module. See
12 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
15 module TcArrows ( tcProc ) where
17 #include "HsVersions.h"
19 import {-# SOURCE #-} TcExpr( tcMonoExpr, tcInferRho )
49 %************************************************************************
53 %************************************************************************
56 tcProc :: InPat Name -> LHsCmdTop Name -- proc pat -> expr
57 -> BoxyRhoType -- Expected type of whole proc expression
58 -> TcM (OutPat TcId, LHsCmdTop TcId, CoercionI)
62 do { ((exp_ty1, res_ty), coi) <- boxySplitAppTy exp_ty
63 ; ((arr_ty, arg_ty), coi1) <- boxySplitAppTy exp_ty1
64 ; let cmd_env = CmdEnv { cmd_arr = arr_ty }
65 ; (pat', cmd') <- tcProcPat pat arg_ty (emptyRefinement, res_ty) $
66 tcCmdTop cmd_env cmd []
67 ; let res_coi = mkTransCoI coi (mkAppTyCoI exp_ty1 coi1 res_ty IdCo)
68 ; return (pat', cmd', res_coi)
73 %************************************************************************
77 %************************************************************************
80 type CmdStack = [TcTauType]
83 cmd_arr :: TcType -- arrow type constructor, of kind *->*->*
86 mkCmdArrTy :: CmdEnv -> TcTauType -> TcTauType -> TcTauType
87 mkCmdArrTy env t1 t2 = mkAppTys (cmd_arr env) [t1, t2]
89 ---------------------------------------
93 -> (Refinement, TcTauType) -- Expected result type; always a monotype
94 -- We know exactly how many cmd args are expected,
95 -- albeit perhaps not their types; so we can pass
97 -> TcM (LHsCmdTop TcId)
99 tcCmdTop env (L loc (HsCmdTop cmd _ _ names)) cmd_stk reft_res_ty@(_,res_ty)
101 do { cmd' <- tcGuardedCmd env cmd cmd_stk reft_res_ty
102 ; names' <- mapM (tcSyntaxName ProcOrigin (cmd_arr env)) names
103 ; return (L loc $ HsCmdTop cmd' cmd_stk res_ty names') }
106 ----------------------------------------
107 tcGuardedCmd :: CmdEnv -> LHsExpr Name -> CmdStack
108 -> (Refinement, TcTauType) -> TcM (LHsExpr TcId)
109 -- A wrapper that deals with the refinement (if any)
110 tcGuardedCmd env expr stk (reft, res_ty)
111 = do { let (co, res_ty') = refineResType reft res_ty
112 ; body <- tcCmd env expr (stk, res_ty')
113 ; return (mkLHsWrap co body) }
115 tcCmd :: CmdEnv -> LHsExpr Name -> (CmdStack, TcTauType) -> TcM (LHsExpr TcId)
116 -- The main recursive function
117 tcCmd env (L loc expr) res_ty
118 = setSrcSpan loc $ do
119 { expr' <- tc_cmd env expr res_ty
120 ; return (L loc expr') }
122 tc_cmd env (HsPar cmd) res_ty
123 = do { cmd' <- tcCmd env cmd res_ty
124 ; return (HsPar cmd') }
126 tc_cmd env (HsLet binds (L body_loc body)) res_ty
127 = do { (binds', body') <- tcLocalBinds binds $
128 setSrcSpan body_loc $
129 tc_cmd env body res_ty
130 ; return (HsLet binds' (L body_loc body')) }
132 tc_cmd env in_cmd@(HsCase scrut matches) (stk, res_ty)
133 = addErrCtxt (cmdCtxt in_cmd) $ do
134 (scrut', scrut_ty) <- addErrCtxt (caseScrutCtxt scrut) $
136 matches' <- tcMatchesCase match_ctxt scrut_ty matches res_ty
137 return (HsCase scrut' matches')
139 match_ctxt = MC { mc_what = CaseAlt,
141 mc_body body res_ty' = tcGuardedCmd env body stk res_ty'
143 tc_cmd env (HsIf pred b1 b2) res_ty
144 = do { pred' <- tcMonoExpr pred boolTy
145 ; b1' <- tcCmd env b1 res_ty
146 ; b2' <- tcCmd env b2 res_ty
147 ; return (HsIf pred' b1' b2')
150 -------------------------------------------
152 -- (f -< a) or (f -<< a)
154 tc_cmd env cmd@(HsArrApp fun arg _ ho_app lr) (cmd_stk, res_ty)
155 = addErrCtxt (cmdCtxt cmd) $
156 do { arg_ty <- newFlexiTyVarTy openTypeKind
157 ; let fun_ty = mkCmdArrTy env (foldl mkPairTy arg_ty cmd_stk) res_ty
159 ; fun' <- select_arrow_scope (tcMonoExpr fun fun_ty)
161 ; arg' <- tcMonoExpr arg arg_ty
163 ; return (HsArrApp fun' arg' fun_ty ho_app lr) }
165 -- Before type-checking f, use the environment of the enclosing
166 -- proc for the (-<) case.
167 -- Local bindings, inside the enclosing proc, are not in scope
168 -- inside f. In the higher-order case (-<<), they are.
169 select_arrow_scope tc = case ho_app of
170 HsHigherOrderApp -> tc
171 HsFirstOrderApp -> escapeArrowScope tc
173 -------------------------------------------
174 -- Command application
176 tc_cmd env cmd@(HsApp fun arg) (cmd_stk, res_ty)
177 = addErrCtxt (cmdCtxt cmd) $
179 do { arg_ty <- newFlexiTyVarTy openTypeKind
181 ; fun' <- tcCmd env fun (arg_ty:cmd_stk, res_ty)
183 ; arg' <- tcMonoExpr arg arg_ty
185 ; return (HsApp fun' arg') }
187 -------------------------------------------
190 tc_cmd env cmd@(HsLam (MatchGroup [L mtch_loc (match@(Match pats maybe_rhs_sig grhss))] _))
192 = addErrCtxt (matchCtxt match_ctxt match) $
194 do { -- Check the cmd stack is big enough
195 ; checkTc (lengthAtLeast cmd_stk n_pats)
198 -- Check the patterns, and the GRHSs inside
199 ; (pats', grhss') <- setSrcSpan mtch_loc $
200 tcLamPats pats cmd_stk res_ty $
203 ; let match' = L mtch_loc (Match pats' Nothing grhss')
204 ; return (HsLam (MatchGroup [match'] res_ty))
209 stk' = drop n_pats cmd_stk
210 match_ctxt = (LambdaExpr :: HsMatchContext Name) -- Maybe KappaExpr?
211 pg_ctxt = PatGuard match_ctxt
213 tc_grhss (GRHSs grhss binds) res_ty
214 = do { (binds', grhss') <- tcLocalBinds binds $
215 mapM (wrapLocM (tc_grhs res_ty)) grhss
216 ; return (GRHSs grhss' binds') }
218 tc_grhs res_ty (GRHS guards body)
219 = do { (guards', rhs') <- tcStmts pg_ctxt tcGuardStmt guards res_ty $
220 tcGuardedCmd env body stk'
221 ; return (GRHS guards' rhs') }
223 -------------------------------------------
226 tc_cmd env cmd@(HsDo do_or_lc stmts body ty) (cmd_stk, res_ty)
227 = do { checkTc (null cmd_stk) (nonEmptyCmdStkErr cmd)
228 ; (stmts', body') <- tcStmts do_or_lc tc_stmt stmts (emptyRefinement, res_ty) $
229 tcGuardedCmd env body []
230 ; return (HsDo do_or_lc stmts' body' res_ty) }
232 tc_stmt = tcMDoStmt tc_rhs
233 tc_rhs rhs = do { ty <- newFlexiTyVarTy liftedTypeKind
234 ; rhs' <- tcCmd env rhs ([], ty)
235 ; return (rhs', ty) }
238 -----------------------------------------------------------------
239 -- Arrow ``forms'' (| e c1 .. cn |)
241 -- G |-b c : [s1 .. sm] s
242 -- pop(G) |- e : forall w. b ((w,s1) .. sm) s
243 -- -> a ((w,t1) .. tn) t
244 -- e \not\in (s, s1..sm, t, t1..tn)
245 -- ----------------------------------------------
246 -- G |-a (| e c |) : [t1 .. tn] t
248 tc_cmd env cmd@(HsArrForm expr fixity cmd_args) (cmd_stk, res_ty)
249 = addErrCtxt (cmdCtxt cmd) $
250 do { cmds_w_tys <- zipWithM new_cmd_ty cmd_args [1..]
251 ; span <- getSrcSpanM
252 ; [w_tv] <- tcInstSkolTyVars ArrowSkol [alphaTyVar]
253 ; let w_ty = mkTyVarTy w_tv -- Just a convenient starting point
255 -- a ((w,t1) .. tn) t
256 ; let e_res_ty = mkCmdArrTy env (foldl mkPairTy w_ty cmd_stk) res_ty
258 -- b ((w,s1) .. sm) s
259 -- -> a ((w,t1) .. tn) t
260 ; let e_ty = mkFunTys [mkAppTys b [tup,s] | (_,_,b,tup,s) <- cmds_w_tys]
264 ; (expr', lie) <- escapeArrowScope (getLIE (tcMonoExpr expr e_ty))
265 ; loc <- getInstLoc (SigOrigin ArrowSkol)
266 ; inst_binds <- tcSimplifyCheck loc [w_tv] [] lie
268 -- Check that the polymorphic variable hasn't been unified with anything
269 -- and is not free in res_ty or the cmd_stk (i.e. t, t1..tn)
270 ; checkSigTyVarsWrt (tyVarsOfTypes (res_ty:cmd_stk)) [w_tv]
272 -- OK, now we are in a position to unscramble
273 -- the s1..sm and check each cmd
274 ; cmds' <- mapM (tc_cmd w_tv) cmds_w_tys
276 ; return (HsArrForm (noLoc $ HsWrap (WpTyLam w_tv)
277 (unLoc $ mkHsDictLet inst_binds expr'))
282 -- b, ((e,s1) .. sm), s
283 new_cmd_ty :: LHsCmdTop Name -> Int
284 -> TcM (LHsCmdTop Name, Int, TcType, TcType, TcType)
286 = do { b_ty <- newFlexiTyVarTy arrowTyConKind
287 ; tup_ty <- newFlexiTyVarTy liftedTypeKind
288 -- We actually make a type variable for the tuple
289 -- because we don't know how deeply nested it is yet
290 ; s_ty <- newFlexiTyVarTy liftedTypeKind
291 ; return (cmd, i, b_ty, tup_ty, s_ty)
294 tc_cmd w_tv (cmd, i, b, tup_ty, s)
295 = do { tup_ty' <- zonkTcType tup_ty
296 ; let (corner_ty, arg_tys) = unscramble tup_ty'
298 -- Check that it has the right shape:
300 -- where the si do not mention w
301 ; checkTc (corner_ty `tcEqType` mkTyVarTy w_tv &&
302 not (w_tv `elemVarSet` tyVarsOfTypes arg_tys))
303 (badFormFun i tup_ty')
305 ; tcCmdTop (env { cmd_arr = b }) cmd arg_tys (emptyRefinement, s) }
307 unscramble :: TcType -> (TcType, [TcType])
308 -- unscramble ((w,s1) .. sn) = (w, [s1..sn])
310 = case tcSplitTyConApp_maybe ty of
311 Just (tc, [t,s]) | tc == pairTyCon
313 (w,ss) = unscramble t
318 -----------------------------------------------------------------
319 -- Base case for illegal commands
320 -- This is where expressions that aren't commands get rejected
323 = failWithTc (vcat [ptext SLIT("The expression"), nest 2 (ppr cmd),
324 ptext SLIT("was found where an arrow command was expected")])
328 %************************************************************************
332 %************************************************************************
336 mkPairTy t1 t2 = mkTyConApp pairTyCon [t1,t2]
338 arrowTyConKind :: Kind -- *->*->*
339 arrowTyConKind = mkArrowKinds [liftedTypeKind, liftedTypeKind] liftedTypeKind
343 %************************************************************************
347 %************************************************************************
350 cmdCtxt cmd = ptext SLIT("In the command:") <+> ppr cmd
353 = hang (ptext SLIT("In the scrutinee of a case command:")) 4 (ppr cmd)
355 nonEmptyCmdStkErr cmd
356 = hang (ptext SLIT("Non-empty command stack at command:"))
360 = hang (ptext SLIT("Command stack underflow at command:"))
364 = hang (ptext SLIT("The type of the") <+> speakNth i <+> ptext SLIT("argument of a command form has the wrong shape"))
365 4 (ptext SLIT("Argument type:") <+> ppr tup_ty')