TcBinds.lhs 42.9 KB
Newer Older
1
%
2
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
3 4 5 6
%
\section[TcBinds]{TcBinds}

\begin{code}
7 8
module TcBinds ( tcLocalBinds, tcTopBinds, 
		 tcHsBootSigs, tcMonoBinds, 
9 10
		 TcPragFun, tcSpecPrag, tcPrags, mkPragFun, 
		 TcSigInfo(..), TcSigFun, mkTcSigFun,
11
		 badBootDeclErr ) where
12

13
#include "HsVersions.h"
14

ross's avatar
ross committed
15
import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
16
import {-# SOURCE #-} TcExpr  ( tcMonoExpr )
17

18 19
import DynFlags		( dopt, DynFlags,
			  DynFlag(Opt_MonomorphismRestriction, Opt_MonoPatBinds, Opt_GlasgowExts) )
20 21 22 23 24
import HsSyn		( HsExpr(..), HsBind(..), LHsBinds, LHsBind, Sig(..),
			  HsLocalBinds(..), HsValBinds(..), HsIPBinds(..),
			  LSig, Match(..), IPBind(..), Prag(..),
			  HsType(..), LHsType, HsExplicitForAll(..), hsLTyVarNames, 
			  isVanillaLSig, sigName, placeHolderNames, isPragLSig,
25
			  LPat, GRHSs, MatchGroup(..), pprLHsBinds, mkHsCoerce,
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
26
			  collectHsBindBinders, collectPatBinders, pprPatBind, isBangHsBind
27
			)
28
import TcHsSyn		( zonkId )
29

30
import TcRnMonad
31
import Inst		( newDictsAtLoc, newIPDict, instToId )
32
import TcEnv		( tcExtendIdEnv, tcExtendIdEnv2, tcExtendTyVarEnv2, 
33
			  pprBinders, tcLookupLocalId_maybe, tcLookupId,
34
			  tcGetGlobalTyVars )
35
import TcUnify		( tcInfer, tcSubExp, unifyTheta, 
36
			  bleatEscapedTvs, sigCtxt )
37 38
import TcSimplify	( tcSimplifyInfer, tcSimplifyInferCheck, 
			  tcSimplifyRestricted, tcSimplifyIPs )
39
import TcHsType		( tcHsSigType, UserTypeCtxt(..) )
40
import TcPat		( tcPat, PatCtxt(..) )
41
import TcSimplify	( bindInstsOfLocalFuns )
42 43 44 45 46
import TcMType		( newFlexiTyVarTy, zonkQuantifiedTyVar, zonkSigTyVar,
			  tcInstSigTyVars, tcInstSkolTyVars, tcInstType, 
			  zonkTcType, zonkTcTypes, zonkTcTyVars )
import TcType		( TcType, TcTyVar, TcThetaType, 
			  SkolemInfo(SigSkol), UserTypeCtxt(FunSigCtxt), 
47
			  TcTauType, TcSigmaType, isUnboxedTupleType,
48
			  mkTyVarTy, mkForAllTys, mkFunTys, exactTyVarsOfType, 
49
			  mkForAllTy, isUnLiftedType, tcGetTyVar, 
50
			  mkTyVarTys, tidyOpenTyVar )
51
import Kind		( argTypeKind )
52 53
import VarEnv		( TyVarEnv, emptyVarEnv, lookupVarEnv, extendVarEnv ) 
import TysWiredIn	( unitTy )
54
import TysPrim		( alphaTyVar )
55
import Id		( Id, mkLocalId, mkVanillaGlobal )
56
import IdInfo		( vanillaIdInfo )
57
import Var		( TyVar, idType, idName )
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
58
import Name		( Name )
59
import NameSet
60
import NameEnv
61
import VarSet
62
import SrcLoc		( Located(..), unLoc, getLoc )
63
import Bag
64
import ErrUtils		( Message )
65
import Digraph		( SCC(..), stronglyConnComp )
66
import Maybes		( expectJust, isJust, isNothing, orElse )
67 68
import Util		( singleton )
import BasicTypes	( TopLevelFlag(..), isTopLevel, isNotTopLevel,
69
			  RecFlag(..), isNonRec, InlineSpec, defaultInlineSpec )
70
import Outputable
71
\end{code}
72

73

74 75 76 77 78 79
%************************************************************************
%*									*
\subsection{Type-checking bindings}
%*									*
%************************************************************************

80
@tcBindsAndThen@ typechecks a @HsBinds@.  The "and then" part is because
81 82 83 84 85 86 87 88 89 90
it needs to know something about the {\em usage} of the things bound,
so that it can create specialisations of them.  So @tcBindsAndThen@
takes a function which, given an extended environment, E, typechecks
the scope of the bindings returning a typechecked thing and (most
important) an LIE.  It is this LIE which is then used as the basis for
specialising the things bound.

@tcBindsAndThen@ also takes a "combiner" which glues together the
bindings and the "thing" to make a new "thing".

91
The real work is done by @tcBindWithSigsAndThen@.
92 93 94 95 96 97 98 99 100 101

Recursive and non-recursive binds are handled in essentially the same
way: because of uniques there are no scoping issues left.  The only
difference is that non-recursive bindings can bind primitive values.

Even for non-recursive binding groups we add typings for each binder
to the LVE for the following reason.  When each individual binding is
checked the type of its LHS is unified with that of its RHS; and
type-checking the LHS of course requires that the binder is in scope.

102 103 104
At the top-level the LIE is sure to contain nothing but constant
dictionaries, which we resolve at the module level.

105
\begin{code}
106
tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
107 108 109
	-- Note: returning the TcLclEnv is more than we really
	--       want.  The bit we care about is the local bindings
	--	 and the free type variables thereof
110
tcTopBinds binds
111
  = do	{ (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
112
	; return (foldr (unionBags . snd) emptyBag prs, env) }
113
	-- The top level bindings are flattened into a giant 
114
	-- implicitly-mutually-recursive LHsBinds
115

116
tcHsBootSigs :: HsValBinds Name -> TcM [Id]
117 118
-- A hs-boot file has only one BindGroup, and it only has type
-- signatures in it.  The renamer checked all this
119 120
tcHsBootSigs (ValBindsOut binds sigs)
  = do	{ checkTc (null binds) badBootDeclErr
121
	; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
122
  where
123
    tc_boot_sig (TypeSig (L _ name) ty)
124
      = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
125 126
	   ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
	-- Notice that we make GlobalIds, not LocalIds
127
tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
128

129 130 131
badBootDeclErr :: Message
badBootDeclErr = ptext SLIT("Illegal declarations in an hs-boot file")

132 133 134
------------------------
tcLocalBinds :: HsLocalBinds Name -> TcM thing
	     -> TcM (HsLocalBinds TcId, thing)
sof's avatar
sof committed
135

136 137 138
tcLocalBinds EmptyLocalBinds thing_inside 
  = do	{ thing <- thing_inside
	; return (EmptyLocalBinds, thing) }
sof's avatar
sof committed
139

140 141 142
tcLocalBinds (HsValBinds binds) thing_inside
  = do	{ (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
	; return (HsValBinds binds', thing) }
143

144 145 146
tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
  = do	{ (thing, lie) <- getLIE thing_inside
	; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
147 148 149

	-- If the binding binds ?x = E, we  must now 
	-- discharge any ?x constraints in expr_lie
150 151
	; dict_binds <- tcSimplifyIPs avail_ips lie
	; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
152 153 154 155
  where
	-- I wonder if we should do these one at at time
	-- Consider	?x = 4
	--		?y = ?x + 1
156
    tc_ip_bind (IPBind ip expr)
157
      = newFlexiTyVarTy argTypeKind		`thenM` \ ty ->
158
  	newIPDict (IPBindOrigin ip) ip ty	`thenM` \ (ip', ip_inst) ->
159
  	tcMonoExpr expr ty			`thenM` \ expr' ->
160 161
  	returnM (ip_inst, (IPBind ip' expr'))

162 163 164 165 166
------------------------
tcValBinds :: TopLevelFlag 
	   -> HsValBinds Name -> TcM thing
	   -> TcM (HsValBinds TcId, thing) 

167 168 169
tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside
  = pprPanic "tcValBinds" (ppr binds)

170
tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
171
  = do 	{   	-- Typecheck the signature
172
	; let { prag_fn = mkPragFun sigs
173
	      ; ty_sigs = filter isVanillaLSig sigs
174
	      ; sig_fn  = mkTcSigFun ty_sigs }
175 176

	; poly_ids <- mapM tcTySig ty_sigs
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
177 178 179 180 181
		-- No recovery from bad signatures, because the type sigs
		-- may bind type variables, so proceeding without them
		-- can lead to a cascade of errors
		-- ToDo: this means we fall over immediately if any type sig
		-- is wrong, which is over-conservative, see Trac bug #745
182

183 184
		-- Extend the envt right away with all 
		-- the Ids declared with type signatures
185
  	; (binds', thing) <- tcExtendIdEnv poly_ids $
186
			     tc_val_binds top_lvl sig_fn prag_fn 
187
					  binds thing_inside
188

189
	; return (ValBindsOut binds' sigs, thing) }
190

191 192
------------------------
tc_val_binds :: TopLevelFlag -> TcSigFun -> TcPragFun
193
	     -> [(RecFlag, LHsBinds Name)] -> TcM thing
194 195 196 197 198 199 200 201
	     -> TcM ([(RecFlag, LHsBinds TcId)], thing)
-- Typecheck a whole lot of value bindings,
-- one strongly-connected component at a time

tc_val_binds top_lvl sig_fn prag_fn [] thing_inside
  = do	{ thing <- thing_inside
	; return ([], thing) }

202
tc_val_binds top_lvl sig_fn prag_fn (group : groups) thing_inside
203
  = do	{ (group', (groups', thing))
204 205
		<- tc_group top_lvl sig_fn prag_fn group $ 
		   tc_val_binds top_lvl sig_fn prag_fn groups thing_inside
206
	; return (group' ++ groups', thing) }
sof's avatar
sof committed
207

208 209
------------------------
tc_group :: TopLevelFlag -> TcSigFun -> TcPragFun
210
	 -> (RecFlag, LHsBinds Name) -> TcM thing
211 212 213 214 215 216
 	 -> TcM ([(RecFlag, LHsBinds TcId)], thing)

-- Typecheck one strongly-connected component of the original program.
-- We get a list of groups back, because there may 
-- be specialisations etc as well

217
tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
218 219 220
  =  	-- A single non-recursive binding
     	-- We want to keep non-recursive things non-recursive
        -- so that we desugar unlifted bindings correctly
221 222
    do	{ (binds, thing) <- tcPolyBinds top_lvl NonRecursive NonRecursive
					sig_fn prag_fn binds thing_inside
223 224
	; return ([(NonRecursive, b) | b <- binds], thing) }

225
tc_group top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
226
  =	-- A recursive strongly-connected component
227
 	-- To maximise polymorphism (with -fglasgow-exts), we do a new 
228
	-- strongly-connected-component analysis, this time omitting 
229
	-- any references to variables with type signatures.
230 231
	--
	-- Then we bring into scope all the variables with type signatures
232
    do	{ traceTc (text "tc_group rec" <+> pprLHsBinds binds)
233 234 235
	; gla_exts     <- doptM Opt_GlasgowExts
	; (binds,thing) <- if gla_exts 
			   then go new_sccs
236
			   else tc_binds Recursive binds thing_inside
237 238 239
	; return ([(Recursive, unionManyBags binds)], thing) }
		-- Rec them all together
  where
240
    new_sccs :: [SCC (LHsBind Name)]
241
    new_sccs = stronglyConnComp (mkEdges sig_fn binds)
242

243 244 245 246
--  go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], thing)
    go (scc:sccs) = do	{ (binds1, (binds2, thing)) <- go1 scc (go sccs)
			; return (binds1 ++ binds2, thing) }
    go [] 	  = do	{ thing <- thing_inside; return ([], thing) }
sof's avatar
sof committed
247

248 249
    go1 (AcyclicSCC bind) = tc_binds NonRecursive (unitBag bind)
    go1 (CyclicSCC binds) = tc_binds Recursive    (listToBag binds)
sof's avatar
sof committed
250

251 252 253 254 255 256 257 258 259
    tc_binds rec_tc binds = tcPolyBinds top_lvl Recursive rec_tc sig_fn prag_fn binds

------------------------
mkEdges :: TcSigFun -> LHsBinds Name
	-> [(LHsBind Name, BKey, [BKey])]

type BKey  = Int -- Just number off the bindings

mkEdges sig_fn binds
260 261
  = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
			 Just key <- [lookupNameEnv key_map n], no_sig n ])
262 263 264 265 266 267 268 269 270 271 272 273 274
    | (bind, key) <- keyd_binds
    ]
  where
    no_sig :: Name -> Bool
    no_sig n = isNothing (sig_fn n)

    keyd_binds = bagToList binds `zip` [0::BKey ..]

    key_map :: NameEnv BKey	-- Which binding it comes from
    key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
				     , bndr <- bindersOfHsBind bind ]

bindersOfHsBind :: HsBind Name -> [Name]
275 276
bindersOfHsBind (PatBind { pat_lhs = pat })  = collectPatBinders pat
bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
277

278
------------------------
279 280 281
tcPolyBinds :: TopLevelFlag 
	    -> RecFlag			-- Whether the group is really recursive
	    -> RecFlag			-- Whether it's recursive for typechecking purposes
282
	    -> TcSigFun -> TcPragFun
283
	    -> LHsBinds Name
284 285 286 287 288 289 290 291
 	    -> TcM thing
	    -> TcM ([LHsBinds TcId], thing)

-- Typechecks a single bunch of bindings all together, 
-- and generalises them.  The bunch may be only part of a recursive
-- group, because we use type signatures to maximise polymorphism
--
-- Deals with the bindInstsOfLocalFuns thing too
292 293 294 295
--
-- Returns a list because the input may be a single non-recursive binding,
-- in which case the dependency order of the resulting bindings is
-- important.  
296

297
tcPolyBinds top_lvl rec_group rec_tc sig_fn prag_fn scc thing_inside
298 299 300
  =	-- NB: polymorphic recursion means that a function
	-- may use an instance of itself, we must look at the LIE arising
	-- from the function's own right hand side.  Hence the getLIE
301 302
	-- encloses the tc_poly_binds. 
    do	{ traceTc (text "tcPolyBinds" <+> ppr scc)
303
	; ((binds1, poly_ids, thing), lie) <- getLIE $ 
304
		do { (binds1, poly_ids) <- tc_poly_binds top_lvl rec_group rec_tc
305 306 307 308 309 310 311 312 313 314 315 316 317 318 319
							 sig_fn prag_fn scc
		   ; thing <- tcExtendIdEnv poly_ids thing_inside
		   ; return (binds1, poly_ids, thing) }

	; if isTopLevel top_lvl 
	  then		-- For the top level don't bother will all this
			-- bindInstsOfLocalFuns stuff. All the top level 
			-- things are rec'd together anyway, so it's fine to
		        -- leave them to the tcSimplifyTop, 
			-- and quite a bit faster too
		do { extendLIEs lie; return (binds1, thing) }

	  else do	-- Nested case
		{ lie_binds <- bindInstsOfLocalFuns lie poly_ids
	 	; return (binds1 ++ [lie_binds], thing) }}
320

321
------------------------
322 323
tc_poly_binds :: TopLevelFlag		-- See comments on tcPolyBinds
	      -> RecFlag -> RecFlag
324
	      -> TcSigFun -> TcPragFun
325
	      -> LHsBinds Name
326 327 328 329
	      -> TcM ([LHsBinds TcId], [TcId])
-- Typechecks the bindings themselves
-- Knows nothing about the scope of the bindings

330
tc_poly_binds top_lvl rec_group rec_tc sig_fn prag_fn binds
331
  = let 
332 333
        binder_names = collectHsBindBinders binds
	bind_list    = bagToList binds
334

335
	loc = getLoc (head bind_list)
336 337 338
		-- TODO: location a bit awkward, but the mbinds have been
		--	 dependency analysed and may no longer be adjacent
    in
339
	-- SET UP THE MAIN RECOVERY; take advantage of any type sigs
340
    setSrcSpan loc				$
341
    recoverM (recoveryCode binder_names)	$ do 
342

343 344
  { traceTc (ptext SLIT("------------------------------------------------"))
  ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
345 346

   	-- TYPECHECK THE BINDINGS
347
  ; ((binds', mono_bind_infos), lie_req) 
348
	<- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
349

350 351 352 353
	-- CHECK FOR UNLIFTED BINDINGS
	-- These must be non-recursive etc, and are not generalised
	-- They desugar to a case expression in the end
  ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
354 355 356 357 358
  ; is_strict <- checkStrictBinds top_lvl rec_group binds' 
				  zonked_mono_tys mono_bind_infos
  ; if is_strict then
    do	{ extendLIEs lie_req
	; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
359 360
	      mk_export (name, Nothing,  mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
	      mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig,             mono_id, [])
361
			-- ToDo: prags for unlifted bindings
362

363 364
	; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
		   [poly_id | (_, poly_id, _, _) <- exports]) }	-- Guaranteed zonked
365 366

    else do	-- The normal lifted case: GENERALISE
367
  { dflags <- getDOpts 
368
  ; (tyvars_to_gen, dict_binds, dict_ids)
369
	<- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
370
	   generalise dflags top_lvl bind_list sig_fn mono_bind_infos lie_req
371 372 373 374 375 376

	-- FINALISE THE QUANTIFIED TYPE VARIABLES
	-- The quantified type variables often include meta type variables
	-- we want to freeze them into ordinary type variables, and
	-- default their kind (e.g. from OpenTypeKind to TypeKind)
  ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
377 378

	-- BUILD THE POLYMORPHIC RESULT IDs
379 380
  ; exports <- mapM (mkExport prag_fn tyvars_to_gen' (map idType dict_ids))
		    mono_bind_infos
sof's avatar
sof committed
381

382 383
	-- ZONK THE poly_ids, because they are used to extend the type 
	-- environment; see the invariant on TcEnv.tcExtendIdEnv 
384
  ; let	poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
385 386
  ; zonked_poly_ids <- mappM zonkId poly_ids

387
  ; traceTc (text "binding:" <+> ppr (zonked_poly_ids `zip` map idType zonked_poly_ids))
388 389 390 391 392 393 394 395 396 397 398 399 400

  ; let abs_bind = L loc $ AbsBinds tyvars_to_gen'
	 		            dict_ids exports
	 		    	    (dict_binds `unionBags` binds')

  ; return ([unitBag abs_bind], zonked_poly_ids)
  } }


--------------
mkExport :: TcPragFun -> [TyVar] -> [TcType] -> MonoBindInfo
	 -> TcM ([TyVar], Id, Id, [Prag])
mkExport prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418
  = case mb_sig of
      Nothing  -> do { prags <- tcPrags poly_id (prag_fn poly_name)
		     ; return (inferred_tvs, poly_id, mono_id, prags) }
	  where
	    poly_id = mkLocalId poly_name poly_ty
	    poly_ty = mkForAllTys inferred_tvs
				       $ mkFunTys dict_tys 
				       $ idType mono_id

      Just sig -> do { let poly_id = sig_id sig
		     ; prags <- tcPrags poly_id (prag_fn poly_name)
		     ; sig_tys <- zonkTcTyVars (sig_tvs sig)
		     ; let sig_tvs' = map (tcGetTyVar "mkExport") sig_tys
		     ; return (sig_tvs', poly_id, mono_id, prags) }
		-- We zonk the sig_tvs here so that the export triple
		-- always has zonked type variables; 
		-- a convenient invariant

419 420 421 422 423 424 425

------------------------
type TcPragFun = Name -> [LSig Name]

mkPragFun :: [LSig Name] -> TcPragFun
mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
	where
426 427
	  prs = [(expectJust "mkPragFun" (sigName sig), sig) 
		| sig <- sigs, isPragLSig sig]
428 429 430 431 432 433 434 435 436 437 438 439 440
	  env = foldl add emptyNameEnv prs
	  add env (n,p) = extendNameEnv_Acc (:) singleton env n p

tcPrags :: Id -> [LSig Name] -> TcM [Prag]
tcPrags poly_id prags = mapM tc_prag prags
  where
    tc_prag (L loc prag) = setSrcSpan loc $ 
			   addErrCtxt (pragSigCtxt prag) $ 
			   tcPrag poly_id prag

pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)

tcPrag :: TcId -> Sig Name -> TcM Prag
441 442 443
tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl
tcPrag poly_id (SpecInstSig hs_ty)	     = tcSpecPrag poly_id hs_ty defaultInlineSpec
tcPrag poly_id (InlineSig v inl)             = return (InlinePrag inl)
444

445

446 447
tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
tcSpecPrag poly_id hs_ty inl
448
  = do	{ spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
449
	; (co_fn, lie) <- getLIE (tcSubExp (idType poly_id) spec_ty)
450 451
	; extendLIEs lie
	; let const_dicts = map instToId lie
452
	; return (SpecPrag (mkHsCoerce co_fn (HsVar poly_id)) spec_ty const_dicts inl) }
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
453 454
	-- Most of the work of specialisation is done by 
	-- the desugarer, guided by the SpecPrag
455 456
  
--------------
457 458 459
-- If typechecking the binds fails, then return with each
-- signature-less binder given type (forall a.a), to minimise 
-- subsequent error messages
460
recoveryCode binder_names
461
  = do	{ traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
462
	; poly_ids <- mapM mk_dummy binder_names
463
	; return ([], poly_ids) }
464
  where
465 466 467 468 469 470 471 472
    mk_dummy name = do { mb_id <- tcLookupLocalId_maybe name
			; case mb_id of
    		     	      Just id -> return id		-- Had signature, was in envt
	    		      Nothing -> return (mkLocalId name forall_a_a) }    -- No signature

forall_a_a :: TcType
forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)

473

474 475 476
-- Check that non-overloaded unlifted bindings are
-- 	a) non-recursive,
--	b) not top level, 
477 478
--	c) not a multiple-binding group (more or less implied by (a))

simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
479 480 481 482 483
checkStrictBinds :: TopLevelFlag -> RecFlag
		 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
		 -> TcM Bool
checkStrictBinds top_lvl rec_group mbind mono_tys infos
  | unlifted || bang_pat
484
  = do 	{ checkTc (isNotTopLevel top_lvl)
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
485
	  	  (strictBindErr "Top-level" unlifted mbind)
486
	; checkTc (isNonRec rec_group)
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
487
	  	  (strictBindErr "Recursive" unlifted mbind)
488
	; checkTc (isSingletonBag mbind)
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
489 490 491 492 493
	    	  (strictBindErr "Multiple" unlifted mbind) 
	; mapM_ check_sig infos
	; return True }
  | otherwise
  = return False
494
  where
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
495 496
    unlifted = any isUnLiftedType mono_tys
    bang_pat = anyBag (isBangHsBind . unLoc) mbind
497
    check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
498
					 (badStrictSig unlifted sig)
499
    check_sig other	       = return ()
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
500 501 502 503 504 505 506 507 508 509 510 511 512

strictBindErr flavour unlifted mbind
  = hang (text flavour <+> msg <+> ptext SLIT("aren't allowed:")) 4 (ppr mbind)
  where
    msg | unlifted  = ptext SLIT("bindings for unlifted types")
	| otherwise = ptext SLIT("bang-pattern bindings")

badStrictSig unlifted sig
  = hang (ptext SLIT("Illegal polymorphic signature in") <+> msg)
	 4 (ppr sig)
  where
    msg | unlifted  = ptext SLIT("an unlifted binding")
	| otherwise = ptext SLIT("a bang-pattern binding")
513 514
\end{code}

515

516 517
%************************************************************************
%*									*
518
\subsection{tcMonoBind}
519 520 521
%*									*
%************************************************************************

522
@tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
523 524
The signatures have been dealt with already.

525
\begin{code}
526 527
tcMonoBinds :: [LHsBind Name]
	    -> TcSigFun
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
528 529 530
	    -> RecFlag	-- Whether the binding is recursive for typechecking purposes
			-- i.e. the binders are mentioned in their RHSs, and
			--	we are not resuced by a type signature
531 532
	    -> TcM (LHsBinds TcId, [MonoBindInfo])

533 534
tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf, 
				fun_matches = matches, bind_fvs = fvs })]
535
	    sig_fn 		-- Single function binding,
536
	    NonRecursive	-- binder isn't mentioned in RHS,
537
  | Nothing <- sig_fn name	-- ...with no type signature
538 539 540 541 542 543
  = 	-- In this very special case we infer the type of the
	-- right hand side first (it may have a higher-rank type)
	-- and *then* make the monomorphic Id for the LHS
	-- e.g.		f = \(x::forall a. a->a) -> <body>
	-- 	We want to infer a higher-rank type for f
    setSrcSpan b_loc  	$
544
    do	{ ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name matches)
545

546 547 548 549 550 551 552 553
		-- Check for an unboxed tuple type
		--	f = (# True, False #)
		-- Zonk first just in case it's hidden inside a meta type variable
		-- (This shows up as a (more obscure) kind error 
		--  in the 'otherwise' case of tcMonoBinds.)
	; zonked_rhs_ty <- zonkTcType rhs_ty
	; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
		  (unboxedTupleErr name zonked_rhs_ty)
554

555
	; mono_name <- newLocalName name
556
	; let mono_id = mkLocalId mono_name zonked_rhs_ty
557 558 559
	; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
					      fun_matches = matches', bind_fvs = fvs,
					      fun_co_fn = co_fn })),
560 561
		  [(name, Nothing, mono_id)]) }

562 563 564 565
tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf, 
				fun_matches = matches, bind_fvs = fvs })]
	    sig_fn 		-- Single function binding
	    non_rec	
566
  | Just scoped_tvs <- sig_fn name	-- ...with a type signature
567 568 569 570
  = 	-- When we have a single function binding, with a type signature
	-- we can (a) use genuine, rigid skolem constants for the type variables
	--	  (b) bring (rigid) scoped type variables into scope
    setSrcSpan b_loc  	$
571
    do	{ tc_sig <- tcInstSig True name scoped_tvs
572 573 574 575 576 577 578 579 580 581 582 583 584 585 586
	; mono_name <- newLocalName name
	; let mono_ty = sig_tau tc_sig
	      mono_id = mkLocalId mono_name mono_ty
	      rhs_tvs = [ (name, mkTyVarTy tv)
			| (name, tv) <- sig_scoped tc_sig `zip` sig_tvs tc_sig ]

	; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs    $
		    	       tcMatchesFun mono_name matches mono_ty

	; let fun_bind' = FunBind { fun_id = L nm_loc mono_id, 
				    fun_infix = inf, fun_matches = matches',
			            bind_fvs = placeHolderNames, fun_co_fn = co_fn }
	; return (unitBag (L b_loc fun_bind'),
		  [(name, Just tc_sig, mono_id)]) }

587 588
tcMonoBinds binds sig_fn non_rec
  = do	{ tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
589

590
	-- Bring the monomorphic Ids, into scope for the RHSs
591
	; let mono_info  = getMonoBindInfo tc_binds
592 593 594
	      rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
			 	-- A monomorphic binding for each term variable that lacks 
				-- a type sig.  (Ones with a sig are already in scope.)
595

596
	; binds' <- tcExtendIdEnv2    rhs_id_env $
597 598 599 600
		    traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id) 
							 | (n,id) <- rhs_id_env]) `thenM_`
		    mapM (wrapLocM tcRhs) tc_binds
	; return (listToBag binds', mono_info) }
601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621

------------------------
-- tcLhs typechecks the LHS of the bindings, to construct the environment in which
-- we typecheck the RHSs.  Basically what we are doing is this: for each binder:
--	if there's a signature for it, use the instantiated signature type
--	otherwise invent a type variable
-- You see that quite directly in the FunBind case.
-- 
-- But there's a complication for pattern bindings:
--	data T = MkT (forall a. a->a)
--	MkT f = e
-- Here we can guess a type variable for the entire LHS (which will be refined to T)
-- but we want to get (f::forall a. a->a) as the RHS environment.
-- The simplest way to do this is to typecheck the pattern, and then look up the
-- bound mono-ids.  Then we want to retain the typechecked pattern to avoid re-doing
-- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't

data TcMonoBind		-- Half completed; LHS done, RHS not done
  = TcFunBind  MonoBindInfo  (Located TcId) Bool (MatchGroup Name) 
  | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType

622 623 624 625 626 627 628 629 630 631
type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
	-- Type signature (if any), and
	-- the monomorphic bound things

bndrNames :: [MonoBindInfo] -> [Name]
bndrNames mbi = [n | (n,_,_) <- mbi]

getMonoType :: MonoBindInfo -> TcTauType
getMonoType (_,_,mono_id) = idType mono_id

632
tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
633
tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
634
  = do	{ mb_sig <- tcInstSig_maybe sig_fn name
635 636 637 638 639 640
	; mono_name <- newLocalName name
	; mono_ty   <- mk_mono_ty mb_sig
	; let mono_id = mkLocalId mono_name mono_ty
	; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
  where
    mk_mono_ty (Just sig) = return (sig_tau sig)
641 642 643
    mk_mono_ty Nothing    = newFlexiTyVarTy argTypeKind

tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
644
  = do	{ mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
645

646 647 648
	; let nm_sig_prs  = names `zip` mb_sigs
	      tau_sig_env = mkNameEnv [ (name, sig_tau sig) | (name, Just sig) <- nm_sig_prs]
	      sig_tau_fn  = lookupNameEnv tau_sig_env
649

650 651 652 653 654 655 656 657 658 659 660 661
	      tc_pat exp_ty = tcPat (LetPat sig_tau_fn) pat exp_ty unitTy $ \ _ ->
			      mapM lookup_info nm_sig_prs
		-- The unitTy is a bit bogus; it's the "result type" for lookup_info.  

		-- After typechecking the pattern, look up the binder
		-- names, which the pattern has brought into scope.
	      lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
	      lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
					      ; return (name, mb_sig, mono_id) }

	; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
				     tcInfer tc_pat
662

663 664 665 666 667
	; return (TcPatBind infos pat' grhss pat_ty) }
  where
    names = collectPatBinders pat


668
tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
669 670
	-- AbsBind, VarBind impossible

671 672
-------------------
tcRhs :: TcMonoBind -> TcM (HsBind TcId)
673
tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
674 675 676 677
  = do	{ (co_fn, matches') <- tcMatchesFun (idName mono_id) matches 
				    	    (idType mono_id)
	; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
			    bind_fvs = placeHolderNames, fun_co_fn = co_fn }) }
678 679 680

tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
  = do	{ grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
681 682 683
		    tcGRHSsPat grhss pat_ty
	; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty, 
			    bind_fvs = placeHolderNames }) }
684 685 686


---------------------
687
getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
688
getMonoBindInfo tc_binds
689
  = foldr (get_info . unLoc) [] tc_binds
690 691 692 693 694 695 696 697
  where
    get_info (TcFunBind info _ _ _)  rest = info : rest
    get_info (TcPatBind infos _ _ _) rest = infos ++ rest
\end{code}


%************************************************************************
%*									*
698
		Generalisation
699 700 701 702
%*									*
%************************************************************************

\begin{code}
703 704
generalise :: DynFlags -> TopLevelFlag 
	   -> [LHsBind Name] -> TcSigFun 
705
	   -> [MonoBindInfo] -> [Inst]
706
	   -> TcM ([TcTyVar], TcDictBinds, [TcId])
707 708 709 710 711
generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
  | isMonoGroup dflags bind_list
  = do { extendLIEs lie_req; return ([], emptyBag, []) }

  | isRestrictedGroup dflags bind_list sig_fn 	-- RESTRICTED CASE
712 713
  = 	-- Check signature contexts are empty 
    do	{ checkTc (all is_mono_sig sigs)
714
	  	  (restrictedBindCtxtErr bndrs)
715

716 717
	-- Now simplify with exactly that set of tyvars
	-- We have to squash those Methods
718
	; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs 
719
						tau_tvs lie_req
720

721
   	-- Check that signature type variables are OK
722
	; final_qtvs <- checkSigsTyVars qtvs sigs
723

724
	; return (final_qtvs, binds, []) }
725

726 727 728 729
  | null sigs	-- UNRESTRICTED CASE, NO TYPE SIGS
  = tcSimplifyInfer doc tau_tvs lie_req

  | otherwise	-- UNRESTRICTED CASE, WITH TYPE SIGS
730
  = do	{ sig_lie <- unifyCtxts sigs	-- sigs is non-empty
731 732
	; let	-- The "sig_avails" is the stuff available.  We get that from
		-- the context of the type signature, BUT ALSO the lie_avail
733
		-- so that polymorphic recursion works right (see Note [Polymorphic recursion])
734 735
		local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
		sig_avails = sig_lie ++ local_meths
736

737 738
	-- Check that the needed dicts can be
	-- expressed in terms of the signature ones
739
	; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
740 741
	
   	-- Check that signature type variables are OK
742
	; final_qtvs <- checkSigsTyVars forall_tvs sigs
743

744
	; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
745
  where
746 747
    bndrs   = bndrNames mono_infos
    sigs    = [sig | (_, Just sig, _) <- mono_infos]
748 749 750
    tau_tvs = foldr (unionVarSet . exactTyVarsOfType . getMonoType) emptyVarSet mono_infos
		-- NB: exactTyVarsOfType; see Note [Silly type synonym] 
		--     near defn of TcType.exactTyVarsOfType
751
    is_mono_sig sig = null (sig_theta sig)
752
    doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
753

754
    mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs, 
755 756 757
		            sig_theta = theta, sig_loc = loc }) mono_id
      = Method mono_id poly_id (mkTyVarTys tvs) theta loc
\end{code}
758

759 760 761
unifyCtxts checks that all the signature contexts are the same
The type signatures on a mutually-recursive group of definitions
must all have the same context (or none).
762

763 764 765 766 767 768 769 770 771
The trick here is that all the signatures should have the same
context, and we want to share type variables for that context, so that
all the right hand sides agree a common vocabulary for their type
constraints

We unify them because, with polymorphic recursion, their types
might not otherwise be related.  This is a rather subtle issue.

\begin{code}
772 773 774 775 776 777 778 779 780 781 782 783
unifyCtxts :: [TcSigInfo] -> TcM [Inst]
unifyCtxts (sig1 : sigs) 	-- Argument is always non-empty
  = do	{ mapM unify_ctxt sigs
	; newDictsAtLoc (sig_loc sig1) (sig_theta sig1) }
  where
    theta1 = sig_theta sig1
    unify_ctxt :: TcSigInfo -> TcM ()
    unify_ctxt sig@(TcSigInfo { sig_theta = theta })
	= setSrcSpan (instLocSrcSpan (sig_loc sig)) 	$
	  addErrCtxt (sigContextsCtxt sig1 sig)		$
	  unifyTheta theta1 theta

784 785
checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
checkSigsTyVars qtvs sigs 
786 787 788 789 790 791 792 793 794 795 796 797 798 799
  = do	{ gbl_tvs <- tcGetGlobalTyVars
	; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs

	; let	-- Sigh.  Make sure that all the tyvars in the type sigs
		-- appear in the returned ty var list, which is what we are
		-- going to generalise over.  Reason: we occasionally get
		-- silly types like
		--	type T a = () -> ()
		--	f :: T a
		--	f () = ()
		-- Here, 'a' won't appear in qtvs, so we have to add it
	 	sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
		all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
	; returnM all_tvs }
800
  where
801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820
    check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs, 
				  sig_theta = theta, sig_tau = tau})
      = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id))	$
	addErrCtxtM (sigCtxt id tvs theta tau)						$
	do { tvs' <- checkDistinctTyVars tvs
	   ; ifM (any (`elemVarSet` gbl_tvs) tvs')
		 (bleatEscapedTvs gbl_tvs tvs tvs') 
	   ; return tvs' }

checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
-- (checkDistinctTyVars tvs) checks that the tvs from one type signature
-- are still all type variables, and all distinct from each other.  
-- It returns a zonked set of type variables.
-- For example, if the type sig is
--	f :: forall a b. a -> b -> b
-- we want to check that 'a' and 'b' haven't 
--	(a) been unified with a non-tyvar type
--	(b) been unified with each other (all distinct)

checkDistinctTyVars sig_tvs
821
  = do	{ zonked_tvs <- mapM zonkSigTyVar sig_tvs
822 823 824 825 826 827 828 829
	; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
	; return zonked_tvs }
  where
    check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
	-- The TyVarEnv maps each zonked type variable back to its
	-- corresponding user-written signature type variable
    check_dup acc (sig_tv, zonked_tv)
	= case lookupVarEnv acc zonked_tv of
830
		Just sig_tv' -> bomb_out sig_tv sig_tv'
831 832 833

		Nothing -> return (extendVarEnv acc zonked_tv sig_tv)

834
    bomb_out sig_tv1 sig_tv2
835 836 837 838 839 840 841
       = do { env0 <- tcInitTidyEnv
	    ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
		  (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
	          msg = ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1) 
		         <+> ptext SLIT("is unified with another quantified type variable") 
		         <+> quotes (ppr tidy_tv2)
	    ; failWithTcM (env2, msg) }
842 843 844
       where
\end{code}    

845

846
@getTyVarsToGen@ decides what type variables to generalise over.
847 848 849 850 851 852 853 854 855 856 857 858 859 860 861

For a "restricted group" -- see the monomorphism restriction
for a definition -- we bind no dictionaries, and
remove from tyvars_to_gen any constrained type variables

*Don't* simplify dicts at this point, because we aren't going
to generalise over these dicts.  By the time we do simplify them
we may well know more.  For example (this actually came up)
	f :: Array Int Int
	f x = array ... xs where xs = [1,2,3,4,5]
We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
stuff.  If we simplify only at the f-binding (not the xs-binding)
we'll know that the literals are all Ints, and we can just produce
Int literals!

862 863 864 865
Find all the type variables involved in overloading, the
"constrained_tyvars".  These are the ones we *aren't* going to
generalise.  We must be careful about doing this:

866 867 868 869 870 871 872 873
 (a) If we fail to generalise a tyvar which is not actually
	constrained, then it will never, ever get bound, and lands
	up printed out in interface files!  Notorious example:
		instance Eq a => Eq (Foo a b) where ..
	Here, b is not constrained, even though it looks as if it is.
	Another, more common, example is when there's a Method inst in
	the LIE, whose type might very well involve non-overloaded
	type variables.
874 875
  [NOTE: Jan 2001: I don't understand the problem here so I'm doing 
	the simple thing instead]
876

877 878 879 880 881 882 883 884
 (b) On the other hand, we mustn't generalise tyvars which are constrained,
	because we are going to pass on out the unmodified LIE, with those
	tyvars in it.  They won't be in scope if we've generalised them.

So we are careful, and do a complete simplification just to find the
constrained tyvars. We don't use any of the results, except to
find which tyvars are constrained.

885 886 887
Note [Polymorphic recursion]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The game plan for polymorphic recursion in the code above is 
888

889 890 891
	* Bind any variable for which we have a type signature
	  to an Id with a polymorphic type.  Then when type-checking 
	  the RHSs we'll make a full polymorphic call.
892

893 894
This fine, but if you aren't a bit careful you end up with a horrendous
amount of partial application and (worse) a huge space leak. For example:
895

896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925
	f :: Eq a => [a] -> [a]
	f xs = ...f...

If we don't take care, after typechecking we get

	f = /\a -> \d::Eq a -> let f' = f a d
			       in
			       \ys:[a] -> ...f'...

Notice the the stupid construction of (f a d), which is of course
identical to the function we're executing.  In this case, the
polymorphic recursion isn't being used (but that's a very common case).
This can lead to a massive space leak, from the following top-level defn
(post-typechecking)

	ff :: [Int] -> [Int]
	ff = f Int dEqInt

Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
f' is another thunk which evaluates to the same thing... and you end
up with a chain of identical values all hung onto by the CAF ff.

	ff = f Int dEqInt

	   = let f' = f Int dEqInt in \ys. ...f'...

	   = let f' = let f' = f Int dEqInt in \ys. ...f'...
		      in \ys. ...f'...

Etc.
926 927 928 929

NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
which would make the space leak go away in this case

930 931 932 933 934 935
Solution: when typechecking the RHSs we always have in hand the
*monomorphic* Ids for each binding.  So we just need to make sure that
if (Method f a d) shows up in the constraints emerging from (...f...)
we just use the monomorphic Id.  We achieve this by adding monomorphic Ids
to the "givens" when simplifying constraints.  That's what the "lies_avail"
is doing.
936

937 938 939 940 941 942 943 944
Then we get

	f = /\a -> \d::Eq a -> letrec
				 fm = \ys:[a] -> ...fm...
			       in
			       fm


945 946 947

%************************************************************************
%*									*
948
		Signatures
949 950 951
%*									*
%************************************************************************

952
Type signatures are tricky.  See Note [Signature skolems] in TcType
953

954 955 956 957 958 959 960 961 962
@tcSigs@ checks the signatures for validity, and returns a list of
{\em freshly-instantiated} signatures.  That is, the types are already
split up, and have fresh type variables installed.  All non-type-signature
"RenamedSigs" are ignored.

The @TcSigInfo@ contains @TcTypes@ because they are unified with
the variable's type, and after that checked to see whether they've
been instantiated.

963
\begin{code}
964 965 966 967
type TcSigFun = Name -> Maybe [Name]	-- Maps a let-binder to the list of
					-- type variables brought into scope
					-- by its type signature.
					-- Nothing => no type signature
968

969
mkTcSigFun :: [LSig Name] -> TcSigFun
970 971 972
-- Search for a particular type signature
-- Precondition: the sigs are all type sigs
-- Precondition: no duplicates
973
mkTcSigFun sigs = lookupNameEnv env
974
  where
975 976 977 978 979 980 981
    env = mkNameEnv [(name, scoped_tyvars hs_ty)
		    | L span (TypeSig (L _ name) (L _ hs_ty)) <- sigs]
    scoped_tyvars (HsForAllTy Explicit tvs _ _) = hsLTyVarNames tvs
    scoped_tyvars other				= []
	-- The scoped names are the ones explicitly mentioned
	-- in the HsForAll.  (There may be more in sigma_ty, because
	-- of nested type synonyms.  See Note [Scoped] with TcSigInfo.)
982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028

---------------
data TcSigInfo
  = TcSigInfo {
	sig_id     :: TcId,		--  *Polymorphic* binder for this value...

	sig_scoped :: [Name],		-- Names for any scoped type variables
					-- Invariant: correspond 1-1 with an initial
					-- segment of sig_tvs (see Note [Scoped])

	sig_tvs    :: [TcTyVar],	-- Instantiated type variables
					-- See Note [Instantiate sig]

	sig_theta  :: TcThetaType,	-- Instantiated theta
	sig_tau    :: TcTauType,	-- Instantiated tau
	sig_loc    :: InstLoc	 	-- The location of the signature
    }

-- 	Note [Scoped]
-- There may be more instantiated type variables than scoped 
-- ones.  For example:
--	type T a = forall b. b -> (a,b)
--	f :: forall c. T c
-- Here, the signature for f will have one scoped type variable, c,
-- but two instantiated type variables, c' and b'.  
--
-- We assume that the scoped ones are at the *front* of sig_tvs,
-- and remember the names from the original HsForAllTy in sig_scoped

-- 	Note [Instantiate sig]
-- It's vital to instantiate a type signature with fresh variable.
-- For example:
--	type S = forall a. a->a
--	f,g :: S
--	f = ...
--	g = ...
-- Here, we must use distinct type variables when checking f,g's right hand sides.
-- (Instantiation is only necessary because of type synonyms.  Otherwise,
-- it's all cool; each signature has distinct type variables from the renamer.)

instance Outputable TcSigInfo where
    ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
	= ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
\end{code}

\begin{code}
tcTySig :: LSig Name -> TcM TcId
1029
tcTySig (L span (TypeSig (L _ name) ty))
1030
  = setSrcSpan span		$
1031
    do	{ sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1032 1033 1034
	; return (mkLocalId name sigma_ty) }

-------------------