2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section{Typecheck arrow notation}
7 module TcArrows ( tcProc ) where
9 #include "HsVersions.h"
11 import {-# SOURCE #-} TcExpr( tcCheckRho, tcInferRho )
14 import TcHsSyn ( mkHsLet )
16 import TcMatches ( TcStmtCtxt(..), tcMatchPats, matchCtxt, tcStmts,
17 TcMatchCtxt(..), tcMatchesCase )
19 import TcType ( TcType, TcTauType, TcRhoType, mkFunTys, mkTyConApp,
20 mkTyVarTy, mkAppTys, tcSplitTyConApp_maybe, tcEqType,
22 import TcMType ( newTyFlexiVarTy, newTyFlexiVarTys, tcSkolTyVar, zonkTcType )
23 import TcBinds ( tcBindsAndThen )
24 import TcSimplify ( tcSimplifyCheck )
25 import TcUnify ( Expected(..), checkSigTyVarsWrt, zapExpectedTo )
27 import Inst ( tcSyntaxName )
29 import TysWiredIn ( boolTy, pairTyCon )
31 import TysPrim ( alphaTyVar )
32 import Type ( Kind, mkArrowKinds, liftedTypeKind, openTypeKind, tyVarsOfTypes )
34 import SrcLoc ( Located(..) )
36 import Util ( lengthAtLeast )
40 %************************************************************************
44 %************************************************************************
47 tcProc :: InPat Name -> LHsCmdTop Name -- proc pat -> expr
48 -> Expected TcRhoType -- Expected type of whole proc expression
49 -> TcM (OutPat TcId, LHsCmdTop TcId)
53 = do { arr_ty <- newTyFlexiVarTy arrowTyConKind
54 ; [arg_ty, res_ty] <- newTyFlexiVarTys 2 liftedTypeKind
55 ; zapExpectedTo exp_ty (mkAppTys arr_ty [arg_ty,res_ty])
57 ; let cmd_env = CmdEnv { cmd_arr = arr_ty }
58 ; ([pat'], cmd') <- incProcLevel $
59 tcMatchPats [pat] [Check arg_ty] (Check res_ty) $
60 tcCmdTop cmd_env cmd ([], res_ty)
61 -- The False says don't do GADT type refinement
62 -- This is a conservative choice, but I'm not sure of the consequences
63 -- of type refinement in the arrow world!
65 ; return (pat', cmd') }
69 %************************************************************************
73 %************************************************************************
76 type CmdStack = [TcTauType]
77 data CmdEnv = CmdEnv { cmd_arr :: TcType } -- The arrow type constructor, of kind *->*->*
79 mkCmdArrTy :: CmdEnv -> TcTauType -> TcTauType -> TcTauType
80 mkCmdArrTy env t1 t2 = mkAppTys (cmd_arr env) [t1, t2]
82 ---------------------------------------
85 -> (CmdStack, TcTauType) -- Expected result type; always a monotype
86 -- We know exactly how many cmd args are expected,
87 -- albeit perhaps not their types; so we can pass
89 -> TcM (LHsCmdTop TcId)
91 tcCmdTop env (L loc (HsCmdTop cmd _ _ names)) (cmd_stk, res_ty)
93 do { cmd' <- tcCmd env cmd (cmd_stk, res_ty)
94 ; names' <- mapM (tcSyntaxName ProcOrigin (cmd_arr env)) names
95 ; return (L loc $ HsCmdTop cmd' cmd_stk res_ty names') }
98 ----------------------------------------
99 tcCmd :: CmdEnv -> LHsExpr Name -> (CmdStack, TcTauType) -> TcM (LHsExpr TcId)
100 -- The main recursive function
101 tcCmd env (L loc expr) res_ty
102 = setSrcSpan loc $ do
103 { expr' <- tc_cmd env expr res_ty
104 ; return (L loc expr') }
106 tc_cmd env (HsPar cmd) res_ty
107 = do { cmd' <- tcCmd env cmd res_ty
108 ; return (HsPar cmd') }
110 tc_cmd env (HsLet binds (L body_loc body)) res_ty
111 = tcBindsAndThen glue binds $
112 setSrcSpan body_loc $
113 tc_cmd env body res_ty
115 glue binds expr = HsLet [binds] (L body_loc expr)
117 tc_cmd env in_cmd@(HsCase scrut matches) (stk, res_ty)
118 = addErrCtxt (cmdCtxt in_cmd) $
119 addErrCtxt (caseScrutCtxt scrut) (
121 ) `thenM` \ (scrut', scrut_ty) ->
122 tcMatchesCase match_ctxt scrut_ty matches (Check res_ty) `thenM` \ matches' ->
123 returnM (HsCase scrut' matches')
125 match_ctxt = MC { mc_what = CaseAlt,
127 mc_body body (Check res_ty') = tcCmd env body (stk, res_ty')
129 tc_cmd env (HsIf pred b1 b2) res_ty
130 = do { pred' <- tcCheckRho pred boolTy
131 ; b1' <- tcCmd env b1 res_ty
132 ; b2' <- tcCmd env b2 res_ty
133 ; return (HsIf pred' b1' b2')
136 -------------------------------------------
138 -- (f -< a) or (f -<< a)
140 tc_cmd env cmd@(HsArrApp fun arg _ ho_app lr) (cmd_stk, res_ty)
141 = addErrCtxt (cmdCtxt cmd) $
142 do { arg_ty <- newTyFlexiVarTy openTypeKind
143 ; let fun_ty = mkCmdArrTy env (foldl mkPairTy arg_ty cmd_stk) res_ty
145 ; fun' <- pop_arrow_binders (tcCheckRho fun fun_ty)
147 ; arg' <- tcCheckRho arg arg_ty
149 ; return (HsArrApp fun' arg' fun_ty ho_app lr) }
151 -- Before type-checking f, remove the "arrow binders" from the
152 -- environment in the (-<) case.
153 -- Local bindings, inside the enclosing proc, are not in scope
154 -- inside f. In the higher-order case (-<<), they are.
155 pop_arrow_binders tc = case ho_app of
156 HsHigherOrderApp -> tc
157 HsFirstOrderApp -> popArrowBinders tc
159 -------------------------------------------
160 -- Command application
162 tc_cmd env cmd@(HsApp fun arg) (cmd_stk, res_ty)
163 = addErrCtxt (cmdCtxt cmd) $
165 do { arg_ty <- newTyFlexiVarTy openTypeKind
167 ; fun' <- tcCmd env fun (arg_ty:cmd_stk, res_ty)
169 ; arg' <- tcCheckRho arg arg_ty
171 ; return (HsApp fun' arg') }
173 -------------------------------------------
177 tc_cmd env cmd@(HsLam (MatchGroup [L mtch_loc (match@(Match pats maybe_rhs_sig grhss))] _))
179 = addErrCtxt (matchCtxt match_ctxt match) $
181 do { -- Check the cmd stack is big enough
182 ; checkTc (lengthAtLeast cmd_stk n_pats)
185 -- Check the patterns, and the GRHSs inside
186 ; (pats', grhss') <- setSrcSpan mtch_loc $
187 tcMatchPats pats (map Check cmd_stk) (Check res_ty) $
190 ; let match' = L mtch_loc (Match pats' Nothing grhss')
191 ; return (HsLam (MatchGroup [match'] res_ty))
196 stk' = drop n_pats cmd_stk
197 match_ctxt = LambdaExpr -- Maybe KappaExpr?
199 tc_grhss (GRHSs grhss binds)
200 = tcBindsAndThen glueBindsOnGRHSs binds $
201 do { grhss' <- mappM (wrapLocM tc_grhs) grhss
202 ; return (GRHSs grhss' []) }
204 stmt_ctxt = SC { sc_what = PatGuard match_ctxt,
206 sc_body = \ body -> tcCmd env body (stk', res_ty),
207 sc_ty = res_ty } -- ToDo: Is this right?
208 tc_grhs (GRHS guarded)
209 = do { guarded' <- tcStmts stmt_ctxt guarded
210 ; return (GRHS guarded') }
212 -------------------------------------------
215 tc_cmd env cmd@(HsDo do_or_lc stmts _ ty) (cmd_stk, res_ty)
216 = do { checkTc (null cmd_stk) (nonEmptyCmdStkErr cmd)
217 ; stmts' <- tcStmts stmt_ctxt stmts
218 ; return (HsDo do_or_lc stmts' [] res_ty) }
219 -- The 'methods' needed for the HsDo are in the enclosing HsCmd
220 -- hence the empty list here
222 stmt_ctxt = SC { sc_what = do_or_lc,
227 tc_rhs rhs = do { ty <- newTyFlexiVarTy liftedTypeKind
228 ; rhs' <- tcCmd env rhs ([], ty)
229 ; return (rhs', ty) }
230 tc_ret body = tcCmd env body ([], res_ty)
233 -----------------------------------------------------------------
234 -- Arrow ``forms'' (| e |) c1 .. cn
236 -- G |-b c : [s1 .. sm] s
237 -- pop(G) |- e : forall w. b ((w,s1) .. sm) s
238 -- -> a ((w,t1) .. tn) t
239 -- e \not\in (s, s1..sm, t, t1..tn)
240 -- ----------------------------------------------
241 -- G |-a (| e |) c : [t1 .. tn] t
243 tc_cmd env cmd@(HsArrForm expr fixity cmd_args) (cmd_stk, res_ty)
244 = addErrCtxt (cmdCtxt cmd) $
245 do { cmds_w_tys <- zipWithM new_cmd_ty cmd_args [1..]
246 ; span <- getSrcSpanM
247 ; w_tv <- tcSkolTyVar (ArrowSkol span) alphaTyVar
248 ; let w_ty = mkTyVarTy w_tv -- Just a convenient starting point
250 -- a ((w,t1) .. tn) t
251 ; let e_res_ty = mkCmdArrTy env (foldl mkPairTy w_ty cmd_stk) res_ty
253 -- b ((w,s1) .. sm) s
254 -- -> a ((w,t1) .. tn) t
255 ; let e_ty = mkFunTys [mkAppTys b [tup,s] | (_,_,b,tup,s) <- cmds_w_tys]
259 ; (expr', lie) <- getLIE (tcCheckRho expr e_ty)
260 ; inst_binds <- tcSimplifyCheck sig_msg [w_tv] [] lie
262 -- Check that the polymorphic variable hasn't been unified with anything
263 -- and is not free in res_ty or the cmd_stk (i.e. t, t1..tn)
264 ; checkSigTyVarsWrt (tyVarsOfTypes (res_ty:cmd_stk)) [w_tv]
266 -- OK, now we are in a position to unscramble
267 -- the s1..sm and check each cmd
268 ; cmds' <- mapM (tc_cmd w_tv) cmds_w_tys
270 ; returnM (HsArrForm (mkHsTyLam [w_tv] (mkHsLet inst_binds expr')) fixity cmds')
274 -- b, ((e,s1) .. sm), s
275 new_cmd_ty :: LHsCmdTop Name -> Int
276 -> TcM (LHsCmdTop Name, Int, TcType, TcType, TcType)
279 = do { b_ty <- newTyFlexiVarTy arrowTyConKind
280 ; tup_ty <- newTyFlexiVarTy liftedTypeKind
281 -- We actually make a type variable for the tuple
282 -- because we don't know how deeply nested it is yet
283 ; s_ty <- newTyFlexiVarTy liftedTypeKind
284 ; return (cmd, i, b_ty, tup_ty, s_ty)
287 tc_cmd w_tv (cmd, i, b, tup_ty, s)
288 = do { tup_ty' <- zonkTcType tup_ty
289 ; let (corner_ty, arg_tys) = unscramble tup_ty'
291 -- Check that it has the right shape:
293 -- where the si do not mention w
294 ; checkTc (corner_ty `tcEqType` mkTyVarTy w_tv &&
295 not (w_tv `elemVarSet` tyVarsOfTypes arg_tys))
296 (badFormFun i tup_ty')
298 ; tcCmdTop (CmdEnv { cmd_arr = b }) cmd (arg_tys, s) }
300 unscramble :: TcType -> (TcType, [TcType])
301 -- unscramble ((w,s1) .. sn) = (w, [s1..sn])
303 = case tcSplitTyConApp_maybe ty of
304 Just (tc, [t,s]) | tc == pairTyCon
306 (w,ss) = unscramble t
311 sig_msg = ptext SLIT("expected type of a command form")
313 -----------------------------------------------------------------
314 -- Base case for illegal commands
315 -- This is where expressions that aren't commands get rejected
318 = failWithTc (vcat [ptext SLIT("The expression"), nest 2 (ppr cmd),
319 ptext SLIT("was found where an arrow command was expected")])
323 %************************************************************************
327 %************************************************************************
331 mkPairTy t1 t2 = mkTyConApp pairTyCon [t1,t2]
333 arrowTyConKind :: Kind -- *->*->*
334 arrowTyConKind = mkArrowKinds [liftedTypeKind, liftedTypeKind] liftedTypeKind
338 %************************************************************************
342 %************************************************************************
345 cmdCtxt cmd = ptext SLIT("In the command:") <+> ppr cmd
348 = hang (ptext SLIT("In the scrutinee of a case command:")) 4 (ppr cmd)
350 nonEmptyCmdStkErr cmd
351 = hang (ptext SLIT("Non-empty command stack at command:"))
355 = hang (ptext SLIT("Command stack underflow at command:"))
359 = hang (ptext SLIT("The type of the") <+> speakNth i <+> ptext SLIT("argument of a command form has the wrong shape"))
360 4 (ptext SLIT("Argument type:") <+> ppr tup_ty')