TcBinds.lhs 42.2 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 9
module TcBinds ( tcLocalBinds, tcTopBinds, 
		 tcHsBootSigs, tcMonoBinds, 
		 TcPragFun, tcSpecPrag, tcPrags, mkPragFun,
10
		 TcSigInfo(..),
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
import DynFlags		( DynFlag(Opt_MonomorphismRestriction, Opt_GlasgowExts) )
19 20 21 22 23
import HsSyn		( HsExpr(..), HsBind(..), LHsBinds, LHsBind, Sig(..),
			  HsLocalBinds(..), HsValBinds(..), HsIPBinds(..),
			  LSig, Match(..), IPBind(..), Prag(..),
			  HsType(..), LHsType, HsExplicitForAll(..), hsLTyVarNames, 
			  isVanillaLSig, sigName, placeHolderNames, isPragLSig,
24
			  LPat, GRHSs, MatchGroup(..), pprLHsBinds, mkHsCoerce,
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
25
			  collectHsBindBinders, collectPatBinders, pprPatBind, isBangHsBind
26
			)
27
import TcHsSyn		( zonkId )
28

29
import TcRnMonad
30
import Inst		( newDictsAtLoc, newIPDict, instToId )
31
import TcEnv		( tcExtendIdEnv, tcExtendIdEnv2, tcExtendTyVarEnv2, 
32
			  pprBinders, tcLookupLocalId_maybe, tcLookupId,
33
			  tcGetGlobalTyVars )
34
import TcUnify		( tcInfer, tcSubExp, unifyTheta, 
35
			  bleatEscapedTvs, sigCtxt )
36 37
import TcSimplify	( tcSimplifyInfer, tcSimplifyInferCheck, 
			  tcSimplifyRestricted, tcSimplifyIPs )
38
import TcHsType		( tcHsSigType, UserTypeCtxt(..) )
39
import TcPat		( tcPat, PatCtxt(..) )
40
import TcSimplify	( bindInstsOfLocalFuns )
41 42 43 44 45
import TcMType		( newFlexiTyVarTy, zonkQuantifiedTyVar, zonkSigTyVar,
			  tcInstSigTyVars, tcInstSkolTyVars, tcInstType, 
			  zonkTcType, zonkTcTypes, zonkTcTyVars )
import TcType		( TcType, TcTyVar, TcThetaType, 
			  SkolemInfo(SigSkol), UserTypeCtxt(FunSigCtxt), 
46
			  TcTauType, TcSigmaType, isUnboxedTupleType,
47
			  mkTyVarTy, mkForAllTys, mkFunTys, exactTyVarsOfType, 
48
			  mkForAllTy, isUnLiftedType, tcGetTyVar, 
49
			  mkTyVarTys, tidyOpenTyVar )
50
import Kind		( argTypeKind )
51 52
import VarEnv		( TyVarEnv, emptyVarEnv, lookupVarEnv, extendVarEnv ) 
import TysWiredIn	( unitTy )
53
import TysPrim		( alphaTyVar )
54
import Id		( Id, mkLocalId, mkVanillaGlobal )
55
import IdInfo		( vanillaIdInfo )
56
import Var		( TyVar, idType, idName )
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
57
import Name		( Name )
58
import NameSet
59
import NameEnv
60
import VarSet
61
import SrcLoc		( Located(..), unLoc, getLoc )
62
import Bag
63
import ErrUtils		( Message )
64
import Digraph		( SCC(..), stronglyConnComp )
65
import Maybes		( expectJust, isJust, isNothing, orElse )
66 67
import Util		( singleton )
import BasicTypes	( TopLevelFlag(..), isTopLevel, isNotTopLevel,
68
			  RecFlag(..), isNonRec, InlineSpec, defaultInlineSpec )
69
import Outputable
70
\end{code}
71

72

73 74 75 76 77 78
%************************************************************************
%*									*
\subsection{Type-checking bindings}
%*									*
%************************************************************************

79
@tcBindsAndThen@ typechecks a @HsBinds@.  The "and then" part is because
80 81 82 83 84 85 86 87 88 89
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".

90
The real work is done by @tcBindWithSigsAndThen@.
91 92 93 94 95 96 97 98 99 100

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.

101 102 103
At the top-level the LIE is sure to contain nothing but constant
dictionaries, which we resolve at the module level.

104
\begin{code}
105
tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
106 107 108
	-- 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
109
tcTopBinds binds
110
  = do	{ (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
111
	; return (foldr (unionBags . snd) emptyBag prs, env) }
112
	-- The top level bindings are flattened into a giant 
113
	-- implicitly-mutually-recursive LHsBinds
114

115
tcHsBootSigs :: HsValBinds Name -> TcM [Id]
116 117
-- A hs-boot file has only one BindGroup, and it only has type
-- signatures in it.  The renamer checked all this
118 119
tcHsBootSigs (ValBindsOut binds sigs)
  = do	{ checkTc (null binds) badBootDeclErr
120
	; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
121
  where
122
    tc_boot_sig (TypeSig (L _ name) ty)
123
      = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
124 125
	   ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
	-- Notice that we make GlobalIds, not LocalIds
126
tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
127

128 129 130
badBootDeclErr :: Message
badBootDeclErr = ptext SLIT("Illegal declarations in an hs-boot file")

131 132 133
------------------------
tcLocalBinds :: HsLocalBinds Name -> TcM thing
	     -> TcM (HsLocalBinds TcId, thing)
sof's avatar
sof committed
134

135 136 137
tcLocalBinds EmptyLocalBinds thing_inside 
  = do	{ thing <- thing_inside
	; return (EmptyLocalBinds, thing) }
sof's avatar
sof committed
138

139 140 141
tcLocalBinds (HsValBinds binds) thing_inside
  = do	{ (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
	; return (HsValBinds binds', thing) }
142

143 144 145
tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
  = do	{ (thing, lie) <- getLIE thing_inside
	; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
146 147 148

	-- If the binding binds ?x = E, we  must now 
	-- discharge any ?x constraints in expr_lie
149 150
	; dict_binds <- tcSimplifyIPs avail_ips lie
	; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
151 152 153 154
  where
	-- I wonder if we should do these one at at time
	-- Consider	?x = 4
	--		?y = ?x + 1
155
    tc_ip_bind (IPBind ip expr)
156
      = newFlexiTyVarTy argTypeKind		`thenM` \ ty ->
157
  	newIPDict (IPBindOrigin ip) ip ty	`thenM` \ (ip', ip_inst) ->
158
  	tcMonoExpr expr ty			`thenM` \ expr' ->
159 160
  	returnM (ip_inst, (IPBind ip' expr'))

161 162 163 164 165
------------------------
tcValBinds :: TopLevelFlag 
	   -> HsValBinds Name -> TcM thing
	   -> TcM (HsValBinds TcId, thing) 

166 167 168
tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside
  = pprPanic "tcValBinds" (ppr binds)

169
tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
170
  = do 	{   	-- Typecheck the signature
171
	; let { prag_fn = mkPragFun sigs
172 173 174 175
	      ; ty_sigs = filter isVanillaLSig sigs
	      ; sig_fn  = mkSigFun ty_sigs }

	; poly_ids <- mapM tcTySig ty_sigs
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
176 177 178 179 180
		-- 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
181

182 183
		-- Extend the envt right away with all 
		-- the Ids declared with type signatures
184
  	; (binds', thing) <- tcExtendIdEnv poly_ids $
185
			     tc_val_binds top_lvl sig_fn prag_fn 
186
					  binds thing_inside
187

188
	; return (ValBindsOut binds' sigs, thing) }
189

190 191
------------------------
tc_val_binds :: TopLevelFlag -> TcSigFun -> TcPragFun
192
	     -> [(RecFlag, LHsBinds Name)] -> TcM thing
193 194 195 196 197 198 199 200
	     -> 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) }

201
tc_val_binds top_lvl sig_fn prag_fn (group : groups) thing_inside
202
  = do	{ (group', (groups', thing))
203 204
		<- tc_group top_lvl sig_fn prag_fn group $ 
		   tc_val_binds top_lvl sig_fn prag_fn groups thing_inside
205
	; return (group' ++ groups', thing) }
sof's avatar
sof committed
206

207 208
------------------------
tc_group :: TopLevelFlag -> TcSigFun -> TcPragFun
209
	 -> (RecFlag, LHsBinds Name) -> TcM thing
210 211 212 213 214 215
 	 -> 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

216
tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
217 218 219
  =  	-- A single non-recursive binding
     	-- We want to keep non-recursive things non-recursive
        -- so that we desugar unlifted bindings correctly
220 221
    do	{ (binds, thing) <- tcPolyBinds top_lvl NonRecursive NonRecursive
					sig_fn prag_fn binds thing_inside
222 223
	; return ([(NonRecursive, b) | b <- binds], thing) }

224
tc_group top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
225
  =	-- A recursive strongly-connected component
226
 	-- To maximise polymorphism (with -fglasgow-exts), we do a new 
227
	-- strongly-connected-component analysis, this time omitting 
228
	-- any references to variables with type signatures.
229 230
	--
	-- Then we bring into scope all the variables with type signatures
231
    do	{ traceTc (text "tc_group rec" <+> pprLHsBinds binds)
232 233 234
	; gla_exts     <- doptM Opt_GlasgowExts
	; (binds,thing) <- if gla_exts 
			   then go new_sccs
235
			   else tc_binds Recursive binds thing_inside
236 237 238
	; return ([(Recursive, unionManyBags binds)], thing) }
		-- Rec them all together
  where
239
    new_sccs :: [SCC (LHsBind Name)]
240
    new_sccs = stronglyConnComp (mkEdges sig_fn binds)
241

242 243 244 245
--  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
246

247 248
    go1 (AcyclicSCC bind) = tc_binds NonRecursive (unitBag bind)
    go1 (CyclicSCC binds) = tc_binds Recursive    (listToBag binds)
sof's avatar
sof committed
249

250 251 252 253 254 255 256 257 258
    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
259 260
  = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
			 Just key <- [lookupNameEnv key_map n], no_sig n ])
261 262 263 264 265 266 267 268 269 270 271 272 273
    | (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]
274 275
bindersOfHsBind (PatBind { pat_lhs = pat })  = collectPatBinders pat
bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
276

277
------------------------
278 279 280
tcPolyBinds :: TopLevelFlag 
	    -> RecFlag			-- Whether the group is really recursive
	    -> RecFlag			-- Whether it's recursive for typechecking purposes
281
	    -> TcSigFun -> TcPragFun
282
	    -> LHsBinds Name
283 284 285 286 287 288 289 290
 	    -> 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
291 292 293 294
--
-- 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.  
295

296
tcPolyBinds top_lvl rec_group rec_tc sig_fn prag_fn scc thing_inside
297 298 299
  =	-- 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
300 301
	-- encloses the tc_poly_binds. 
    do	{ traceTc (text "tcPolyBinds" <+> ppr scc)
302
	; ((binds1, poly_ids, thing), lie) <- getLIE $ 
303
		do { (binds1, poly_ids) <- tc_poly_binds top_lvl rec_group rec_tc
304 305 306 307 308 309 310 311 312 313 314 315 316 317 318
							 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) }}
319

320
------------------------
321 322
tc_poly_binds :: TopLevelFlag		-- See comments on tcPolyBinds
	      -> RecFlag -> RecFlag
323
	      -> TcSigFun -> TcPragFun
324
	      -> LHsBinds Name
325 326 327 328
	      -> TcM ([LHsBinds TcId], [TcId])
-- Typechecks the bindings themselves
-- Knows nothing about the scope of the bindings

329
tc_poly_binds top_lvl rec_group rec_tc sig_fn prag_fn binds
330
  = let 
331 332
        binder_names = collectHsBindBinders binds
	bind_list    = bagToList binds
333

334
	loc = getLoc (head bind_list)
335 336 337
		-- TODO: location a bit awkward, but the mbinds have been
		--	 dependency analysed and may no longer be adjacent
    in
338
	-- SET UP THE MAIN RECOVERY; take advantage of any type sigs
339
    setSrcSpan loc				$
340
    recoverM (recoveryCode binder_names)	$ do 
341

342 343
  { traceTc (ptext SLIT("------------------------------------------------"))
  ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
344 345

   	-- TYPECHECK THE BINDINGS
346
  ; ((binds', mono_bind_infos), lie_req) 
347
	<- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
348

349 350 351 352
	-- 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
353 354 355 356 357
  ; 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
358 359
	      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, [])
360
			-- ToDo: prags for unlifted bindings
361

362 363
	; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
		   [poly_id | (_, poly_id, _, _) <- exports]) }	-- Guaranteed zonked
364 365

    else do	-- The normal lifted case: GENERALISE
366
  { is_unres <- isUnRestrictedGroup bind_list sig_fn
367
  ; (tyvars_to_gen, dict_binds, dict_ids)
368 369
	<- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
	   generalise top_lvl is_unres mono_bind_infos lie_req
370 371 372 373 374 375

	-- 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
376 377

	-- BUILD THE POLYMORPHIC RESULT IDs
378 379
  ; exports <- mapM (mkExport prag_fn tyvars_to_gen' (map idType dict_ids))
		    mono_bind_infos
sof's avatar
sof committed
380

381 382
	-- ZONK THE poly_ids, because they are used to extend the type 
	-- environment; see the invariant on TcEnv.tcExtendIdEnv 
383
  ; let	poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
384 385
  ; zonked_poly_ids <- mappM zonkId poly_ids

386
  ; traceTc (text "binding:" <+> ppr (zonked_poly_ids `zip` map idType zonked_poly_ids))
387 388 389 390 391 392 393 394 395 396 397 398 399

  ; 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)
400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417
  = 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

418 419 420 421 422 423 424

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

mkPragFun :: [LSig Name] -> TcPragFun
mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
	where
425 426
	  prs = [(expectJust "mkPragFun" (sigName sig), sig) 
		| sig <- sigs, isPragLSig sig]
427 428 429 430 431 432 433 434 435 436 437 438 439
	  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
440 441 442
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)
443

444

445 446
tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
tcSpecPrag poly_id hs_ty inl
447
  = do	{ spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
448
	; (co_fn, lie) <- getLIE (tcSubExp (idType poly_id) spec_ty)
449 450
	; extendLIEs lie
	; let const_dicts = map instToId lie
451
	; return (SpecPrag (mkHsCoerce co_fn (HsVar poly_id)) spec_ty const_dicts inl) }
452 453
  
--------------
454 455 456
-- If typechecking the binds fails, then return with each
-- signature-less binder given type (forall a.a), to minimise 
-- subsequent error messages
457
recoveryCode binder_names
458
  = do	{ traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
459
	; poly_ids <- mapM mk_dummy binder_names
460
	; return ([], poly_ids) }
461
  where
462 463 464 465 466 467 468 469
    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)

470

471 472 473
-- Check that non-overloaded unlifted bindings are
-- 	a) non-recursive,
--	b) not top level, 
474 475
--	c) not a multiple-binding group (more or less implied by (a))

simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
476 477 478 479 480
checkStrictBinds :: TopLevelFlag -> RecFlag
		 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
		 -> TcM Bool
checkStrictBinds top_lvl rec_group mbind mono_tys infos
  | unlifted || bang_pat
481
  = do 	{ checkTc (isNotTopLevel top_lvl)
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
482
	  	  (strictBindErr "Top-level" unlifted mbind)
483
	; checkTc (isNonRec rec_group)
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
484
	  	  (strictBindErr "Recursive" unlifted mbind)
485
	; checkTc (isSingletonBag mbind)
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
486 487 488 489 490
	    	  (strictBindErr "Multiple" unlifted mbind) 
	; mapM_ check_sig infos
	; return True }
  | otherwise
  = return False
491
  where
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
492 493
    unlifted = any isUnLiftedType mono_tys
    bang_pat = anyBag (isBangHsBind . unLoc) mbind
494
    check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
495
					 (badStrictSig unlifted sig)
496
    check_sig other	       = return ()
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
497 498 499 500 501 502 503 504 505 506 507 508 509

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")
510 511
\end{code}

512

513 514
%************************************************************************
%*									*
515
\subsection{tcMonoBind}
516 517 518
%*									*
%************************************************************************

519
@tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
520 521
The signatures have been dealt with already.

522
\begin{code}
523 524
tcMonoBinds :: [LHsBind Name]
	    -> TcSigFun
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
525 526 527
	    -> 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
528 529
	    -> TcM (LHsBinds TcId, [MonoBindInfo])

530 531
tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf, 
				fun_matches = matches, bind_fvs = fvs })]
532
	    sig_fn 		-- Single function binding,
533
	    NonRecursive	-- binder isn't mentioned in RHS,
534
  | Nothing <- sig_fn name	-- ...with no type signature
535 536 537 538 539 540
  = 	-- 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  	$
541
    do	{ ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name matches)
542

543 544 545 546 547 548 549 550
		-- 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)
551

552
	; mono_name <- newLocalName name
553
	; let mono_id = mkLocalId mono_name zonked_rhs_ty
554 555 556
	; 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 })),
557 558
		  [(name, Nothing, mono_id)]) }

559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583
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	
  | Just sig <- sig_fn name	-- ...with a type signature
  = 	-- 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  	$
    do	{ tc_sig <- tcInstSig True sig
	; 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)]) }

584 585
tcMonoBinds binds sig_fn non_rec
  = do	{ tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
586

587
	-- Bring the monomorphic Ids, into scope for the RHSs
588
	; let mono_info  = getMonoBindInfo tc_binds
589 590 591
	      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.)
592

593
	; binds' <- tcExtendIdEnv2    rhs_id_env $
594 595 596 597
		    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) }
598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618

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

619 620 621 622 623 624 625 626 627 628
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

629
tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
630 631
tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
  = do	{ mb_sig <- tcInstSig_maybe (sig_fn name)
632 633 634 635 636 637
	; 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)
638 639 640 641
    mk_mono_ty Nothing    = newFlexiTyVarTy argTypeKind

tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
  = do	{ mb_sigs <- mapM (tcInstSig_maybe . sig_fn) names
642

643 644 645
	; 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
646

647 648 649 650 651 652 653 654 655 656 657 658
	      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
659

660 661 662 663 664
	; return (TcPatBind infos pat' grhss pat_ty) }
  where
    names = collectPatBinders pat


665
tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
666 667
	-- AbsBind, VarBind impossible

668 669
-------------------
tcRhs :: TcMonoBind -> TcM (HsBind TcId)
670
tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
671 672 673 674
  = 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 }) }
675 676 677

tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
  = do	{ grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
678 679 680
		    tcGRHSsPat grhss pat_ty
	; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty, 
			    bind_fvs = placeHolderNames }) }
681 682 683


---------------------
684
getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
685
getMonoBindInfo tc_binds
686
  = foldr (get_info . unLoc) [] tc_binds
687 688 689 690 691 692 693 694
  where
    get_info (TcFunBind info _ _ _)  rest = info : rest
    get_info (TcPatBind infos _ _ _) rest = infos ++ rest
\end{code}


%************************************************************************
%*									*
695
		Generalisation
696 697 698 699
%*									*
%************************************************************************

\begin{code}
700 701
generalise :: TopLevelFlag -> Bool 
	   -> [MonoBindInfo] -> [Inst]
702
	   -> TcM ([TcTyVar], TcDictBinds, [TcId])
703
generalise top_lvl is_unrestricted mono_infos lie_req
704 705 706
  | not is_unrestricted	-- RESTRICTED CASE
  = 	-- Check signature contexts are empty 
    do	{ checkTc (all is_mono_sig sigs)
707
	  	  (restrictedBindCtxtErr bndrs)
708

709 710
	-- Now simplify with exactly that set of tyvars
	-- We have to squash those Methods
711
	; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs 
712
						tau_tvs lie_req
713

714
   	-- Check that signature type variables are OK
715
	; final_qtvs <- checkSigsTyVars qtvs sigs
716

717
	; return (final_qtvs, binds, []) }
718

719 720 721 722
  | null sigs	-- UNRESTRICTED CASE, NO TYPE SIGS
  = tcSimplifyInfer doc tau_tvs lie_req

  | otherwise	-- UNRESTRICTED CASE, WITH TYPE SIGS
723
  = do	{ sig_lie <- unifyCtxts sigs	-- sigs is non-empty
724 725
	; let	-- The "sig_avails" is the stuff available.  We get that from
		-- the context of the type signature, BUT ALSO the lie_avail
726
		-- so that polymorphic recursion works right (see Note [Polymorphic recursion])
727 728
		local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
		sig_avails = sig_lie ++ local_meths
729

730 731
	-- Check that the needed dicts can be
	-- expressed in terms of the signature ones
732
	; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
733 734
	
   	-- Check that signature type variables are OK
735
	; final_qtvs <- checkSigsTyVars forall_tvs sigs
736

737
	; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
738
  where
739 740
    bndrs   = bndrNames mono_infos
    sigs    = [sig | (_, Just sig, _) <- mono_infos]
741 742 743
    tau_tvs = foldr (unionVarSet . exactTyVarsOfType . getMonoType) emptyVarSet mono_infos
		-- NB: exactTyVarsOfType; see Note [Silly type synonym] 
		--     near defn of TcType.exactTyVarsOfType
744
    is_mono_sig sig = null (sig_theta sig)
745
    doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
746

747
    mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs, 
748 749 750
		            sig_theta = theta, sig_loc = loc }) mono_id
      = Method mono_id poly_id (mkTyVarTys tvs) theta loc
\end{code}
751

752 753 754
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).
755

756 757 758 759 760 761 762 763 764
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}
765 766 767 768 769 770 771 772 773 774 775 776
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

777 778
checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
checkSigsTyVars qtvs sigs 
779 780 781 782 783 784 785 786 787 788 789 790 791 792
  = 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 }
793
  where
794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813
    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
814
  = do	{ zonked_tvs <- mapM zonkSigTyVar sig_tvs
815 816 817 818 819 820 821 822
	; 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
823
		Just sig_tv' -> bomb_out sig_tv sig_tv'
824 825 826

		Nothing -> return (extendVarEnv acc zonked_tv sig_tv)

827
    bomb_out sig_tv1 sig_tv2
828 829 830 831 832 833 834
       = 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) }
835 836 837
       where
\end{code}    

838

839
@getTyVarsToGen@ decides what type variables to generalise over.
840 841 842 843 844 845 846 847 848 849 850 851 852 853 854

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!

855 856 857 858
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:

859 860 861 862 863 864 865 866
 (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.
867 868
  [NOTE: Jan 2001: I don't understand the problem here so I'm doing 
	the simple thing instead]
869

870 871 872 873 874 875 876 877
 (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.

878 879 880
Note [Polymorphic recursion]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The game plan for polymorphic recursion in the code above is 
881

882 883 884
	* 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.
885

886 887
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:
888

889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918
	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.
919 920 921 922

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

923 924 925 926 927 928
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.
929

930 931 932 933 934 935 936 937
Then we get

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


938 939 940

%************************************************************************
%*									*
941
		Signatures
942 943 944
%*									*
%************************************************************************

945
Type signatures are tricky.  See Note [Signature skolems] in TcType
946

947 948 949 950 951 952 953 954 955
@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.

956
\begin{code}
957
type TcSigFun = Name -> Maybe (LSig Name)
958

959 960 961 962 963 964
mkSigFun :: [LSig Name] -> TcSigFun
-- Search for a particular type signature
-- Precondition: the sigs are all type sigs
-- Precondition: no duplicates
mkSigFun sigs = lookupNameEnv env
  where
965
    env = mkNameEnv [(expectJust "mkSigFun" (sigName sig), sig) | sig <- sigs]
966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012

---------------
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
1013
tcTySig (L span (TypeSig (L _ name) ty))
1014
  = setSrcSpan span		$
1015
    do	{ sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053
	; return (mkLocalId name sigma_ty) }

-------------------
tcInstSig_maybe :: Maybe (LSig Name) -> TcM (Maybe TcSigInfo)
-- Instantiate with *meta* type variables; 
-- this signature is part of a multi-signature group
tcInstSig_maybe Nothing    = return Nothing
tcInstSig_maybe (Just sig) = do { tc_sig <- tcInstSig False sig
				; return (Just tc_sig) }

tcInstSig :: Bool -> LSig Name -> TcM TcSigInfo
-- Instantiate the signature, with either skolems or meta-type variables
-- depending on the use_skols boolean
--
-- We always instantiate with freshs uniques,
-- although we keep the same print-name
--	
--	type T = forall a. [a] -> [a]
--	f :: T; 
--	f = g where { g :: T; g = <rhs> }
--
-- We must not use the same 'a' from the defn of T at both places!!

tcInstSig use_skols (L loc (TypeSig (L _ name) hs_ty))
  = setSrcSpan loc $
    do	{ poly_id <- tcLookupId name	-- Cannot fail; the poly ids are put into 
					-- scope when starting the binding group
	; let skol_info = SigSkol (FunSigCtxt name)
	      inst_tyvars | use_skols = tcInstSkolTyVars skol_info
			  | otherwise = tcInstSigTyVars  skol_info
	; (tvs, theta, tau) <- tcInstType inst_tyvars (idType poly_id)
	; loc <- getInstLoc (SigOrigin skol_info)
	; return (TcSigInfo { sig_id = poly_id,
			      sig_tvs = tvs, sig_theta = theta, sig_tau = tau, 
			      sig_scoped = scoped_names, sig_loc = loc }) }
		-- Note that the scoped_names and the sig_tvs will have
		-- different Names. That's quite ok; when we bring the 
		-- scoped_names into scope, we just bind them to the sig_tvs
1054 1055 1056 1057
  where
	-- 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.)
1058 1059 1060 1061 1062
	-- We also only have scoped type variables when we are instantiating
	-- with true skolems
    scoped_names = case (use_skols, hs_ty) of
		     (True, L _ (HsForAllTy Explicit tvs _ _)) -> hsLTyVarNames tvs
		     other 		    		       -> []
1063

1064
-------------------
1065 1066 1067 1068 1069 1070 1071 1072
isUnRestrictedGroup :: [LHsBind Name] -> TcSigFun -> TcM Bool