TcBinds.hs 73 KB
Newer Older
Austin Seipp's avatar
Austin Seipp committed
1 2 3 4
{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

5
\section[TcBinds]{TcBinds}
Austin Seipp's avatar
Austin Seipp committed
6
-}
7

8
{-# LANGUAGE CPP, RankNTypes, ScopedTypeVariables #-}
9
{-# LANGUAGE FlexibleContexts #-}
10
{-# LANGUAGE TypeFamilies #-}
11

12
module TcBinds ( tcLocalBinds, tcTopBinds, tcRecSelBinds,
13
                 tcHsBootSigs, tcPolyCheck,
14
                 addTypecheckedBinds,
15 16
                 chooseInferredQuantifiers,
                 badBootDeclErr ) where
17

18 19
import GhcPrelude

20
import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
21
import {-# SOURCE #-} TcExpr  ( tcMonoExpr )
22
import {-# SOURCE #-} TcPatSyn ( tcInferPatSynDecl, tcCheckPatSynDecl
23
                               , tcPatSynBuilderBind )
24
import CoreSyn (Tickish (..))
25
import CostCentre (mkUserCC, CCFlavour(DeclCC))
Simon Marlow's avatar
Simon Marlow committed
26
import DynFlags
27
import FastString
Simon Marlow's avatar
Simon Marlow committed
28
import HsSyn
29
import HscTypes( isHsBootOrSig )
30
import TcSigs
31
import TcRnMonad
Simon Marlow's avatar
Simon Marlow committed
32 33 34
import TcEnv
import TcUnify
import TcSimplify
35
import TcEvidence
Simon Marlow's avatar
Simon Marlow committed
36 37 38
import TcHsType
import TcPat
import TcMType
39 40
import FamInstEnv( normaliseType )
import FamInst( tcGetFamInstEnvs )
41
import TyCon
Simon Marlow's avatar
Simon Marlow committed
42
import TcType
43
import Type( mkStrLitTy, tidyOpenType, splitTyConApp_maybe, mkCastTy)
Simon Marlow's avatar
Simon Marlow committed
44
import TysPrim
45
import TysWiredIn( mkBoxedTupleTy )
Simon Marlow's avatar
Simon Marlow committed
46
import Id
47
import Var
48
import VarSet
49
import VarEnv( TidyEnv )
50
import Module
Simon Marlow's avatar
Simon Marlow committed
51
import Name
52
import NameSet
53
import NameEnv
Simon Marlow's avatar
Simon Marlow committed
54
import SrcLoc
55
import Bag
Simon Marlow's avatar
Simon Marlow committed
56 57 58 59 60
import ErrUtils
import Digraph
import Maybes
import Util
import BasicTypes
61
import Outputable
62
import PrelNames( ipClassName )
63
import TcValidity (checkValidType)
niteria's avatar
niteria committed
64
import UniqFM
David Feuer's avatar
David Feuer committed
65
import UniqSet
66
import qualified GHC.LanguageExtensions as LangExt
67
import ConLike
68 69

import Control.Monad
70 71

#include "HsVersions.h"
72

73 74 75 76 77 78
{- *********************************************************************
*                                                                      *
               A useful helper function
*                                                                      *
********************************************************************* -}

79
addTypecheckedBinds :: TcGblEnv -> [LHsBinds GhcTc] -> TcGblEnv
80
addTypecheckedBinds tcg_env binds
81
  | isHsBootOrSig (tcg_src tcg_env) = tcg_env
82 83 84 85 86 87
    -- Do not add the code for record-selector bindings
    -- when compiling hs-boot files
  | otherwise = tcg_env { tcg_binds = foldr unionBags
                                            (tcg_binds tcg_env)
                                            binds }

Austin Seipp's avatar
Austin Seipp committed
88 89 90
{-
************************************************************************
*                                                                      *
91
\subsection{Type-checking bindings}
Austin Seipp's avatar
Austin Seipp committed
92 93
*                                                                      *
************************************************************************
94

95
@tcBindsAndThen@ typechecks a @HsBinds@.  The "and then" part is because
96 97 98 99 100 101 102 103 104 105
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".

106
The real work is done by @tcBindWithSigsAndThen@.
107 108 109 110 111 112 113 114 115 116

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.

117 118 119
At the top-level the LIE is sure to contain nothing but constant
dictionaries, which we resolve at the module level.

120 121
Note [Polymorphic recursion]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
122
The game plan for polymorphic recursion in the code above is
123 124

        * Bind any variable for which we have a type signature
125
          to an Id with a polymorphic type.  Then when type-checking
126 127 128 129 130 131 132 133 134 135 136 137 138 139
          the RHSs we'll make a full polymorphic call.

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:

        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'...

140
Notice the stupid construction of (f a d), which is of course
141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177
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.

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

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.

Then we get

        f = /\a -> \d::Eq a -> letrec
                                 fm = \ys:[a] -> ...fm...
                               in
                               fm
Austin Seipp's avatar
Austin Seipp committed
178
-}
179

180 181
tcTopBinds :: [(RecFlag, LHsBinds GhcRn)] -> [LSig GhcRn]
           -> TcM (TcGblEnv, TcLclEnv)
182 183
-- The TcGblEnv contains the new tcg_binds and tcg_spects
-- The TcLclEnv has an extended type envt for the new bindings
184
tcTopBinds binds sigs
cactus's avatar
cactus committed
185 186 187 188 189
  = do  { -- Pattern synonym bindings populate the global environment
          (binds', (tcg_env, tcl_env)) <- tcValBinds TopLevel binds sigs $
            do { gbl <- getGblEnv
               ; lcl <- getLclEnv
               ; return (gbl, lcl) }
190 191
        ; specs <- tcImpPrags sigs   -- SPECIALISE prags for imported Ids

192 193 194 195 196 197 198 199 200
        ; complete_matches <- setEnvs (tcg_env, tcl_env) $ tcCompleteSigs sigs
        ; traceTc "complete_matches" (ppr binds $$ ppr sigs)
        ; traceTc "complete_matches" (ppr complete_matches)

        ; let { tcg_env' = tcg_env { tcg_imp_specs
                                      = specs ++ tcg_imp_specs tcg_env
                                   , tcg_complete_matches
                                      = complete_matches
                                          ++ tcg_complete_matches tcg_env }
201
                           `addTypecheckedBinds` map snd binds' }
202 203

        ; return (tcg_env', tcl_env) }
204
        -- The top level bindings are flattened into a giant
Ian Lynagh's avatar
Ian Lynagh committed
205
        -- implicitly-mutually-recursive LHsBinds
cactus's avatar
cactus committed
206

207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231

-- Note [Typechecking Complete Matches]
-- Much like when a user bundled a pattern synonym, the result types of
-- all the constructors in the match pragma must be consistent.
--
-- If we allowed pragmas with inconsistent types then it would be
-- impossible to ever match every constructor in the list and so
-- the pragma would be useless.





-- This is only used in `tcCompleteSig`. We fold over all the conlikes,
-- this accumulator keeps track of the first `ConLike` with a concrete
-- return type. After fixing the return type, all other constructors with
-- a fixed return type must agree with this.
--
-- The fields of `Fixed` cache the first conlike and its return type so
-- that that we can compare all the other conlikes to it. The conlike is
-- stored for error messages.
--
-- `Nothing` in the case that the type is fixed by a type signature
data CompleteSigType = AcceptAny | Fixed (Maybe ConLike) TyCon

232
tcCompleteSigs  :: [LSig GhcRn] -> TcM [CompleteMatch]
233 234
tcCompleteSigs sigs =
  let
235
      doOne :: Sig GhcRn -> TcM (Maybe CompleteMatch)
236
      doOne c@(CompleteMatchSig _ _ lns mtc)
237 238 239 240 241 242 243 244 245 246 247 248 249
        = fmap Just $ do
           addErrCtxt (text "In" <+> ppr c) $
            case mtc of
              Nothing -> infer_complete_match
              Just tc -> check_complete_match tc
        where

          checkCLTypes acc = foldM checkCLType (acc, []) (unLoc lns)

          infer_complete_match = do
            (res, cls) <- checkCLTypes AcceptAny
            case res of
              AcceptAny -> failWithTc ambiguousError
250
              Fixed _ tc  -> return $ mkMatch cls tc
251 252 253 254

          check_complete_match tc_name = do
            ty_con <- tcLookupLocatedTyCon tc_name
            (_, cls) <- checkCLTypes (Fixed Nothing ty_con)
255 256 257 258 259 260 261
            return $ mkMatch cls ty_con

          mkMatch :: [ConLike] -> TyCon -> CompleteMatch
          mkMatch cls ty_con = CompleteMatch {
            completeMatchConLikes = map conLikeName cls,
            completeMatchTyCon = tyConName ty_con
            }
262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306
      doOne _ = return Nothing

      ambiguousError :: SDoc
      ambiguousError =
        text "A type signature must be provided for a set of polymorphic"
          <+> text "pattern synonyms."


      -- See note [Typechecking Complete Matches]
      checkCLType :: (CompleteSigType, [ConLike]) -> Located Name
                  -> TcM (CompleteSigType, [ConLike])
      checkCLType (cst, cs) n = do
        cl <- addLocM tcLookupConLike n
        let   (_,_,_,_,_,_, res_ty) = conLikeFullSig cl
              res_ty_con = fst <$> splitTyConApp_maybe res_ty
        case (cst, res_ty_con) of
          (AcceptAny, Nothing) -> return (AcceptAny, cl:cs)
          (AcceptAny, Just tc) -> return (Fixed (Just cl) tc, cl:cs)
          (Fixed mfcl tc, Nothing)  -> return (Fixed mfcl tc, cl:cs)
          (Fixed mfcl tc, Just tc') ->
            if tc == tc'
              then return (Fixed mfcl tc, cl:cs)
              else case mfcl of
                     Nothing ->
                      addErrCtxt (text "In" <+> ppr cl) $
                        failWithTc typeSigErrMsg
                     Just cl -> failWithTc (errMsg cl)
             where
              typeSigErrMsg :: SDoc
              typeSigErrMsg =
                text "Couldn't match expected type"
                      <+> quotes (ppr tc)
                      <+> text "with"
                      <+> quotes (ppr tc')

              errMsg :: ConLike -> SDoc
              errMsg fcl =
                text "Cannot form a group of complete patterns from patterns"
                  <+> quotes (ppr fcl) <+> text "and" <+> quotes (ppr cl)
                  <+> text "as they match different type constructors"
                  <+> parens (quotes (ppr tc)
                               <+> text "resp."
                               <+> quotes (ppr tc'))
  in  mapMaybeM (addLocM doOne) sigs

307
tcRecSelBinds :: HsValBinds GhcRn -> TcM TcGblEnv
308
tcRecSelBinds (XValBindsLR (NValBinds binds sigs))
309
  = tcExtendGlobalValEnv [sel_id | L _ (IdSig _ sel_id) <- sigs] $
310 311 312
    do { (rec_sel_binds, tcg_env) <- discardWarnings $
                                     tcValBinds TopLevel binds sigs getGblEnv
       ; let tcg_env' = tcg_env `addTypecheckedBinds` map snd rec_sel_binds
313
       ; return tcg_env' }
314
tcRecSelBinds (ValBinds {}) = panic "tcRecSelBinds"
315

316
tcHsBootSigs :: [(RecFlag, LHsBinds GhcRn)] -> [LSig GhcRn] -> TcM [Id]
317 318
-- A hs-boot file has only one BindGroup, and it only has type
-- signatures in it.  The renamer checked all this
319
tcHsBootSigs binds sigs
Ian Lynagh's avatar
Ian Lynagh committed
320
  = do  { checkTc (null binds) badBootDeclErr
321
        ; concat <$> mapM (addLocM tc_boot_sig) (filter isTypeLSig sigs) }
322
  where
323
    tc_boot_sig (TypeSig _ lnames hs_ty) = mapM f lnames
324
      where
325
        f (L _ name)
Richard Eisenberg's avatar
Richard Eisenberg committed
326
          = do { sigma_ty <- tcHsSigWcType (FunSigCtxt name False) hs_ty
327
               ; return (mkVanillaGlobal name sigma_ty) }
Ian Lynagh's avatar
Ian Lynagh committed
328
        -- Notice that we make GlobalIds, not LocalIds
Ian Lynagh's avatar
Ian Lynagh committed
329
    tc_boot_sig s = pprPanic "tcHsBootSigs/tc_boot_sig" (ppr s)
330

331
badBootDeclErr :: MsgDoc
332
badBootDeclErr = text "Illegal declarations in an hs-boot file"
333

334
------------------------
335 336
tcLocalBinds :: HsLocalBinds GhcRn -> TcM thing
             -> TcM (HsLocalBinds GhcTcId, thing)
sof's avatar
sof committed
337

338
tcLocalBinds (EmptyLocalBinds x) thing_inside
Ian Lynagh's avatar
Ian Lynagh committed
339
  = do  { thing <- thing_inside
340
        ; return (EmptyLocalBinds x, thing) }
sof's avatar
sof committed
341

342
tcLocalBinds (HsValBinds x (XValBindsLR (NValBinds binds sigs))) thing_inside
343
  = do  { (binds', thing) <- tcValBinds NotTopLevel binds sigs thing_inside
344 345
        ; return (HsValBinds x (XValBindsLR (NValBinds binds' sigs)), thing) }
tcLocalBinds (HsValBinds _ (ValBinds {})) _ = panic "tcLocalBinds"
346

347
tcLocalBinds (HsIPBinds x (IPBinds _ ip_binds)) thing_inside
348 349
  = do  { ipClass <- tcLookupClass ipClassName
        ; (given_ips, ip_binds') <-
350
            mapAndUnzipM (wrapLocSndM (tc_ip_bind ipClass)) ip_binds
351

352
        -- If the binding binds ?x = E, we  must now
Ian Lynagh's avatar
Ian Lynagh committed
353
        -- discharge any ?x constraints in expr_lie
354
        -- See Note [Implicit parameter untouchables]
355
        ; (ev_binds, result) <- checkConstraints (IPSkol ips)
356
                                  [] given_ips thing_inside
357

358
        ; return (HsIPBinds x (IPBinds ev_binds ip_binds') , result) }
359
  where
360
    ips = [ip | L _ (IPBind _ (Left (L _ ip)) _) <- ip_binds]
361

Ian Lynagh's avatar
Ian Lynagh committed
362 363 364
        -- I wonder if we should do these one at at time
        -- Consider     ?x = 4
        --              ?y = ?x + 1
365
    tc_ip_bind ipClass (IPBind _ (Left (L _ ip)) expr)
366
       = do { ty <- newOpenFlexiTyVarTy
367 368
            ; let p = mkStrLitTy $ hsIPNameFS ip
            ; ip_id <- newDict ipClass [ p, ty ]
369
            ; expr' <- tcMonoExpr expr (mkCheckExpType ty)
370
            ; let d = toDict ipClass p ty `fmap` expr'
371 372 373
            ; return (ip_id, (IPBind noExt (Right ip_id) d)) }
    tc_ip_bind _ (IPBind _ (Right {}) _) = panic "tc_ip_bind"
    tc_ip_bind _ (XCIPBind _) = panic "tc_ip_bind"
374 375 376

    -- Coerces a `t` into a dictionry for `IP "x" t`.
    -- co : t -> IP "x" t
377
    toDict ipClass x ty = mkHsWrap $ mkWpCastR $
378
                          wrapIP $ mkClassPred ipClass [x,ty]
379

380 381 382
tcLocalBinds (HsIPBinds _ (XHsIPBinds _ )) _ = panic "tcLocalBinds"
tcLocalBinds (XHsLocalBindsLR _)           _ = panic "tcLocalBinds"

383 384
{- Note [Implicit parameter untouchables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
385 386 387 388 389
We add the type variables in the types of the implicit parameters
as untouchables, not so much because we really must not unify them,
but rather because we otherwise end up with constraints like this
    Num alpha, Implic { wanted = alpha ~ Int }
The constraint solver solves alpha~Int by unification, but then
390
doesn't float that solved constraint out (it's not an unsolved
391
wanted).  Result disaster: the (Num alpha) is again solved, this
392 393
time by defaulting.  No no no.

394
However [Oct 10] this is all handled automatically by the
395
untouchable-range idea.
Austin Seipp's avatar
Austin Seipp committed
396
-}
397

398
tcValBinds :: TopLevelFlag
399
           -> [(RecFlag, LHsBinds GhcRn)] -> [LSig GhcRn]
400
           -> TcM thing
401
           -> TcM ([(RecFlag, LHsBinds GhcTcId)], thing)
402

403
tcValBinds top_lvl binds sigs thing_inside
404 405 406 407
  = do  { let patsyns = getPatSynBinds binds

            -- Typecheck the signature
        ; (poly_ids, sig_fn) <- tcAddPatSynPlaceholders patsyns $
408
                                tcTySigs sigs
Ian Lynagh's avatar
Ian Lynagh committed
409

410 411
        ; let prag_fn = mkPragEnv sigs (foldr (unionBags . snd) emptyBag binds)

412 413
                -- Extend the envt right away with all the Ids
                -- declared with complete type signatures
414
                -- Do not extend the TcBinderStack; instead
415
                -- we extend it on a per-rhs basis in tcExtendForRhs
416
        ; tcExtendSigIds top_lvl poly_ids $ do
417 418
            { (binds', (extra_binds', thing)) <- tcBindGroups top_lvl sig_fn prag_fn binds $ do
                   { thing <- thing_inside
419
                     -- See Note [Pattern synonym builders don't yield dependencies]
420
                     --     in RnBinds
421
                   ; patsyn_builders <- mapM tcPatSynBuilderBind patsyns
422
                   ; let extra_binds = [ (NonRecursive, builder) | builder <- patsyn_builders ]
423
                   ; return (extra_binds, thing) }
424
            ; return (binds' ++ extra_binds', thing) }}
425

426
------------------------
427
tcBindGroups :: TopLevelFlag -> TcSigFun -> TcPragEnv
428 429
             -> [(RecFlag, LHsBinds GhcRn)] -> TcM thing
             -> TcM ([(RecFlag, LHsBinds GhcTcId)], thing)
430 431
-- Typecheck a whole lot of value bindings,
-- one strongly-connected component at a time
432
-- Here a "strongly connected component" has the strightforward
433
-- meaning of a group of bindings that mention each other,
434
-- ignoring type signatures (that part comes later)
435

436
tcBindGroups _ _ _ [] thing_inside
Ian Lynagh's avatar
Ian Lynagh committed
437 438
  = do  { thing <- thing_inside
        ; return ([], thing) }
439

440
tcBindGroups top_lvl sig_fn prag_fn (group : groups) thing_inside
441
  = do  { -- See Note [Closed binder groups]
442 443
          type_env <- getLclTypeEnv
        ; let closed = isClosedBndrGroup type_env (snd group)
444 445
        ; (group', (groups', thing))
                <- tc_group top_lvl sig_fn prag_fn group closed $
446
                   tcBindGroups top_lvl sig_fn prag_fn groups thing_inside
Ian Lynagh's avatar
Ian Lynagh committed
447
        ; return (group' ++ groups', thing) }
sof's avatar
sof committed
448

449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465
-- Note [Closed binder groups]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
--  A mutually recursive group is "closed" if all of the free variables of
--  the bindings are closed. For example
--
-- >  h = \x -> let f = ...g...
-- >                g = ....f...x...
-- >             in ...
--
-- Here @g@ is not closed because it mentions @x@; and hence neither is @f@
-- closed.
--
-- So we need to compute closed-ness on each strongly connected components,
-- before we sub-divide it based on what type signatures it has.
--

466
------------------------
467
tc_group :: forall thing.
468
            TopLevelFlag -> TcSigFun -> TcPragEnv
469 470
         -> (RecFlag, LHsBinds GhcRn) -> IsGroupClosed -> TcM thing
         -> TcM ([(RecFlag, LHsBinds GhcTcId)], thing)
471 472

-- Typecheck one strongly-connected component of the original program.
473
-- We get a list of groups back, because there may
474 475
-- be specialisations etc as well

476
tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) closed thing_inside
Ian Lynagh's avatar
Ian Lynagh committed
477 478
        -- A single non-recursive binding
        -- We want to keep non-recursive things non-recursive
479
        -- so that we desugar unlifted bindings correctly
cactus's avatar
cactus committed
480 481
  = do { let bind = case bagToList binds of
                 [bind] -> bind
482 483
                 []     -> panic "tc_group: empty list of binds"
                 _      -> panic "tc_group: NonRecursive binds is not a singleton bag"
484 485
       ; (bind', thing) <- tc_single top_lvl sig_fn prag_fn bind closed
                                     thing_inside
cactus's avatar
cactus committed
486
       ; return ( [(NonRecursive, bind')], thing) }
487

488
tc_group top_lvl sig_fn prag_fn (Recursive, binds) closed thing_inside
489 490
  =     -- To maximise polymorphism, we do a new
        -- strongly-connected-component analysis, this time omitting
Ian Lynagh's avatar
Ian Lynagh committed
491
        -- any references to variables with type signatures.
492
        -- (This used to be optional, but isn't now.)
493
        -- See Note [Polymorphic recursion] in HsBinds.
494
    do  { traceTc "tc_group rec" (pprLHsBinds binds)
cactus's avatar
cactus committed
495
        ; when hasPatSyn $ recursivePatSynErr binds
496
        ; (binds1, thing) <- go sccs
497
        ; return ([(Recursive, binds1)], thing) }
Ian Lynagh's avatar
Ian Lynagh committed
498
                -- Rec them all together
499
  where
500
    hasPatSyn = anyBag (isPatSyn . unLoc) binds
cactus's avatar
cactus committed
501 502 503
    isPatSyn PatSynBind{} = True
    isPatSyn _ = False

504
    sccs :: [SCC (LHsBind GhcRn)]
niteria's avatar
niteria committed
505
    sccs = stronglyConnCompFromEdgedVerticesUniq (mkEdges sig_fn binds)
506

507
    go :: [SCC (LHsBind GhcRn)] -> TcM (LHsBinds GhcTcId, thing)
508
    go (scc:sccs) = do  { (binds1, ids1) <- tc_scc scc
509 510 511
                        ; (binds2, thing) <- tcExtendLetEnv top_lvl sig_fn
                                                            closed ids1 $
                                             go sccs
512 513
                        ; return (binds1 `unionBags` binds2, thing) }
    go []         = do  { thing <- thing_inside; return (emptyBag, thing) }
514

515 516
    tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive [bind]
    tc_scc (CyclicSCC binds) = tc_sub_group Recursive    binds
sof's avatar
sof committed
517

518
    tc_sub_group rec_tc binds =
519
      tcPolyBinds sig_fn prag_fn Recursive rec_tc closed binds
sof's avatar
sof committed
520

521
recursivePatSynErr :: OutputableBndrId name => LHsBinds name -> TcM a
cactus's avatar
cactus committed
522 523
recursivePatSynErr binds
  = failWithTc $
524
    hang (text "Recursive pattern synonym definition with following bindings:")
525
       2 (vcat $ map pprLBind . bagToList $ binds)
cactus's avatar
cactus committed
526
  where
527
    pprLoc loc  = parens (text "defined at" <+> ppr loc)
cactus's avatar
cactus committed
528 529 530 531
    pprLBind (L loc bind) = pprWithCommas ppr (collectHsBindBinders bind) <+>
                            pprLoc loc

tc_single :: forall thing.
532
            TopLevelFlag -> TcSigFun -> TcPragEnv
533 534
          -> LHsBind GhcRn -> IsGroupClosed -> TcM thing
          -> TcM (LHsBinds GhcTcId, thing)
535
tc_single _top_lvl sig_fn _prag_fn
536
          (L _ (PatSynBind _ psb@PSB{ psb_id = L _ name }))
537
          _ thing_inside
538 539
  = do { (aux_binds, tcg_env) <- tc_pat_syn_decl
       ; thing <- setGblEnv tcg_env thing_inside
cactus's avatar
cactus committed
540 541
       ; return (aux_binds, thing)
       }
542
  where
543
    tc_pat_syn_decl :: TcM (LHsBinds GhcTcId, TcGblEnv)
544
    tc_pat_syn_decl = case sig_fn name of
545 546 547
        Nothing                 -> tcInferPatSynDecl psb
        Just (TcPatSynSig tpsi) -> tcCheckPatSynDecl psb tpsi
        Just                 _  -> panic "tc_single"
548

549
tc_single top_lvl sig_fn prag_fn lbind closed thing_inside
550
  = do { (binds1, ids) <- tcPolyBinds sig_fn prag_fn
551
                                      NonRecursive NonRecursive
552
                                      closed
553
                                      [lbind]
554
       ; thing <- tcExtendLetEnv top_lvl sig_fn closed ids thing_inside
cactus's avatar
cactus committed
555
       ; return (binds1, thing) }
556

557
------------------------
558
type BKey = Int -- Just number off the bindings
559

560
mkEdges :: TcSigFun -> LHsBinds GhcRn -> [Node BKey (LHsBind GhcRn)]
561
-- See Note [Polymorphic recursion] in HsBinds.
562
mkEdges sig_fn binds
563 564
  = [ DigraphNode bind key [key | n <- nonDetEltsUniqSet (bind_fvs (unLoc bind)),
                         Just key <- [lookupNameEnv key_map n], no_sig n ]
565 566
    | (bind, key) <- keyd_binds
    ]
niteria's avatar
niteria committed
567 568 569
    -- It's OK to use nonDetEltsUFM here as stronglyConnCompFromEdgedVertices
    -- is still deterministic even if the edges are in nondeterministic order
    -- as explained in Note [Deterministic SCC] in Digraph.
570
  where
571 572 573 574
    bind_fvs (FunBind { fun_ext = fvs }) = fvs
    bind_fvs (PatBind { pat_ext = fvs }) = fvs
    bind_fvs _                           = emptyNameSet

575
    no_sig :: Name -> Bool
576
    no_sig n = not (hasCompleteSig sig_fn n)
577 578 579

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

Ian Lynagh's avatar
Ian Lynagh committed
580
    key_map :: NameEnv BKey     -- Which binding it comes from
581
    key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
582
                                     , bndr <- collectHsBindBinders bind ]
583

584
------------------------
585
tcPolyBinds :: TcSigFun -> TcPragEnv
586 587 588
            -> RecFlag         -- Whether the group is really recursive
            -> RecFlag         -- Whether it's recursive after breaking
                               -- dependencies based on type signatures
589
            -> IsGroupClosed   -- Whether the group is closed
590 591
            -> [LHsBind GhcRn]  -- None are PatSynBind
            -> TcM (LHsBinds GhcTcId, [TcId])
592

593
-- Typechecks a single bunch of values bindings all together,
594 595 596
-- and generalises them.  The bunch may be only part of a recursive
-- group, because we use type signatures to maximise polymorphism
--
597 598
-- Returns a list because the input may be a single non-recursive binding,
-- in which case the dependency order of the resulting bindings is
599 600
-- important.
--
601
-- Knows nothing about the scope of the bindings
602
-- None of the bindings are pattern synonyms
603

604
tcPolyBinds sig_fn prag_fn rec_group rec_tc closed bind_list
605
  = setSrcSpan loc                              $
606
    recoverM (recoveryCode binder_names sig_fn) $ do
607
        -- Set up main recover; take advantage of any type sigs
608

609
    { traceTc "------------------------------------------------" Outputable.empty
610
    ; traceTc "Bindings for {" (ppr binder_names)
611
    ; dflags   <- getDynFlags
612
    ; let plan = decideGeneralisationPlan dflags bind_list closed sig_fn
613
    ; traceTc "Generalisation plan" (ppr plan)
614
    ; result@(_, poly_ids) <- case plan of
615 616
         NoGen              -> tcPolyNoGen rec_tc prag_fn sig_fn bind_list
         InferGen mn        -> tcPolyInfer rec_tc prag_fn sig_fn mn bind_list
617
         CheckGen lbind sig -> tcPolyCheck prag_fn sig lbind
618

619 620 621
    ; traceTc "} End of bindings for" (vcat [ ppr binder_names, ppr rec_group
                                            , vcat [ppr id <+> ppr (idType id) | id <- poly_ids]
                                          ])
622

623
    ; return result }
624
  where
625 626
    binder_names = collectHsBindListBinders bind_list
    loc = foldr1 combineSrcSpans (map getLoc bind_list)
627
         -- The mbinds have been dependency analysed and
628
         -- may no longer be adjacent; so find the narrowest
chak@cse.unsw.edu.au.'s avatar
chak@cse.unsw.edu.au. committed
629
         -- span that includes them all
630

631 632 633 634
--------------
-- If typechecking the binds fails, then return with each
-- signature-less binder given type (forall a.a), to minimise
-- subsequent error messages
635
recoveryCode :: [Name] -> TcSigFun -> TcM (LHsBinds GhcTcId, [Id])
636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656
recoveryCode binder_names sig_fn
  = do  { traceTc "tcBindsWithSigs: error recovery" (ppr binder_names)
        ; let poly_ids = map mk_dummy binder_names
        ; return (emptyBag, poly_ids) }
  where
    mk_dummy name
      | Just sig <- sig_fn name
      , Just poly_id <- completeSigPolyId_maybe sig
      = poly_id
      | otherwise
      = mkLocalId name forall_a_a

forall_a_a :: TcType
forall_a_a = mkSpecForAllTys [runtimeRep1TyVar, openAlphaTyVar] openAlphaTy

{- *********************************************************************
*                                                                      *
                         tcPolyNoGen
*                                                                      *
********************************************************************* -}

657
tcPolyNoGen     -- No generalisation whatsoever
658
  :: RecFlag       -- Whether it's recursive after breaking
659
                   -- dependencies based on type signatures
660
  -> TcPragEnv -> TcSigFun
661 662
  -> [LHsBind GhcRn]
  -> TcM (LHsBinds GhcTcId, [TcId])
663

664 665
tcPolyNoGen rec_tc prag_fn tc_sig_fn bind_list
  = do { (binds', mono_infos) <- tcMonoBinds rec_tc tc_sig_fn
666
                                             (LetGblBndr prag_fn)
667
                                             bind_list
668
       ; mono_ids' <- mapM tc_mono_info mono_infos
669
       ; return (binds', mono_ids') }
670
  where
eir@cis.upenn.edu's avatar
eir@cis.upenn.edu committed
671
    tc_mono_info (MBI { mbi_poly_name = name, mbi_mono_id = mono_id })
672 673
      = do { _specs <- tcSpecPrags mono_id (lookupPragEnv prag_fn name)
           ; return mono_id }
chak@cse.unsw.edu.au.'s avatar
chak@cse.unsw.edu.au. committed
674 675 676 677
           -- NB: tcPrags generates error messages for
           --     specialisation pragmas for non-overloaded sigs
           -- Indeed that is why we call it here!
           -- So we can safely ignore _specs
678

679 680 681 682 683 684 685 686 687

{- *********************************************************************
*                                                                      *
                         tcPolyCheck
*                                                                      *
********************************************************************* -}

tcPolyCheck :: TcPragEnv
            -> TcIdSigInfo     -- Must be a complete signature
688 689
            -> LHsBind GhcRn   -- Must be a FunBind
            -> TcM (LHsBinds GhcTcId, [TcId])
690
-- There is just one binding,
691
--   it is a Funbind
Simon Peyton Jones's avatar
Simon Peyton Jones committed
692
--   it has a complete type signature,
693 694 695 696 697 698 699 700
tcPolyCheck prag_fn
            (CompleteSig { sig_bndr  = poly_id
                         , sig_ctxt  = ctxt
                         , sig_loc   = sig_loc })
            (L loc (FunBind { fun_id = L nm_loc name
                            , fun_matches = matches }))
  = setSrcSpan sig_loc $
    do { traceTc "tcPolyCheck" (ppr poly_id $$ ppr sig_loc)
701
       ; (tv_prs, theta, tau) <- tcInstType tcInstSkolTyVars poly_id
702 703 704 705 706
                -- See Note [Instantiate sig with fresh variables]

       ; mono_name <- newNameAt (nameOccName name) nm_loc
       ; ev_vars   <- newEvVars theta
       ; let mono_id   = mkLocalId mono_name tau
707
             skol_info = SigSkol ctxt (idType poly_id) tv_prs
708 709 710 711
             skol_tvs  = map snd tv_prs

       ; (ev_binds, (co_fn, matches'))
            <- checkConstraints skol_info skol_tvs ev_vars $
712
               tcExtendBinderStack [TcIdBndr mono_id NotTopLevel]  $
713
               tcExtendNameTyVarEnv tv_prs $
714 715 716 717
               setSrcSpan loc           $
               tcMatchesFun (L nm_loc mono_name) matches (mkCheckExpType tau)

       ; let prag_sigs = lookupPragEnv prag_fn name
718 719
       ; spec_prags <- tcSpecPrags poly_id prag_sigs
       ; poly_id    <- addInlinePrags poly_id prag_sigs
720

721
       ; mod <- getModule
722
       ; tick <- funBindTicks nm_loc mono_id mod prag_sigs
723 724 725
       ; let bind' = FunBind { fun_id      = L nm_loc mono_id
                             , fun_matches = matches'
                             , fun_co_fn   = co_fn
726
                             , fun_ext     = placeHolderNamesTc
727
                             , fun_tick    = tick }
728

729 730
             export = ABE { abe_ext = noExt
                          , abe_wrap = idHsWrapper
731 732 733 734 735
                          , abe_poly  = poly_id
                          , abe_mono  = mono_id
                          , abe_prags = SpecPrags spec_prags }

             abs_bind = L loc $
736 737
                        AbsBinds { abs_ext = noExt
                                 , abs_tvs      = skol_tvs
738 739 740 741 742
                                 , abs_ev_vars  = ev_vars
                                 , abs_ev_binds = [ev_binds]
                                 , abs_exports  = [export]
                                 , abs_binds    = unitBag (L loc bind')
                                 , abs_sig      = True }
eir@cis.upenn.edu's avatar
eir@cis.upenn.edu committed
743

744
       ; return (unitBag abs_bind, [poly_id]) }
745

746 747 748
tcPolyCheck _prag_fn sig bind
  = pprPanic "tcPolyCheck" (ppr sig $$ ppr bind)

749
funBindTicks :: SrcSpan -> TcId -> Module -> [LSig GhcRn]
750
             -> TcM [Tickish TcId]
751
funBindTicks loc fun_id mod sigs
752
  | (mb_cc_str : _) <- [ cc_name | L _ (SCCFunSig _ _ _ cc_name) <- sigs ]
753 754 755 756
      -- this can only be a singleton list, as duplicate pragmas are rejected
      -- by the renamer
  , let cc_str
          | Just cc_str <- mb_cc_str
757
          = sl_fs $ unLoc cc_str
758 759 760
          | otherwise
          = getOccFS (Var.varName fun_id)
        cc_name = moduleNameFS (moduleName mod) `appendFS` consFS '.' cc_str
761 762 763 764
  = do
      flavour <- DeclCC <$> getCCIndexM cc_name
      let cc = mkUserCC cc_name mod loc flavour
      return [ProfNote cc True True]
765
  | otherwise
766
  = return []
767

768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786
{- Note [Instantiate sig with fresh variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's vital to instantiate a type signature with fresh variables.
For example:
      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!!
(Instantiation is only necessary because of type synonyms.  Otherwise,
it's all cool; each signature has distinct type variables from the renamer.)
-}


{- *********************************************************************
*                                                                      *
                         tcPolyInfer
*                                                                      *
********************************************************************* -}
787 788

tcPolyInfer
789
  :: RecFlag       -- Whether it's recursive after breaking
790
                   -- dependencies based on type signatures
791
  -> TcPragEnv -> TcSigFun
792
  -> Bool         -- True <=> apply the monomorphism restriction
793 794
  -> [LHsBind GhcRn]
  -> TcM (LHsBinds GhcTcId, [TcId])
795
tcPolyInfer rec_tc prag_fn tc_sig_fn mono bind_list
796
  = do { (tclvl, wanted, (binds', mono_infos))
797
             <- pushLevelAndCaptureConstraints  $
798 799
                tcMonoBinds rec_tc tc_sig_fn LetLclBndr bind_list

800 801 802 803
       ; let name_taus  = [ (mbi_poly_name info, idType (mbi_mono_id info))
                          | info <- mono_infos ]
             sigs       = [ sig | MBI { mbi_sig = Just sig } <- mono_infos ]
             infer_mode = if mono then ApplyMR else NoRestrictions
804

805 806
       ; mapM_ (checkOverloadedSig mono) sigs

807
       ; traceTc "simplifyInfer call" (ppr tclvl $$ ppr name_taus $$ ppr wanted)
808
       ; (qtvs, givens, ev_binds, insoluble)
809
                 <- simplifyInfer tclvl infer_mode sigs name_taus wanted
810

811
       ; let inferred_theta = map evVarPred givens
812
       ; exports <- checkNoErrs $
813
                    mapM (mkExport prag_fn insoluble qtvs inferred_theta) mono_infos
thomasw's avatar
thomasw committed
814

815
       ; loc <- getSrcSpanM
816
       ; let poly_ids = map abe_poly exports
817
             abs_bind = L loc $
818 819
                        AbsBinds { abs_ext = noExt
                                 , abs_tvs = qtvs
820
                                 , abs_ev_vars = givens, abs_ev_binds = [ev_binds]
821 822
                                 , abs_exports = exports, abs_binds = binds'
                                 , abs_sig = False }
823

824 825
       ; traceTc "Binding:" (ppr (poly_ids `zip` map idType poly_ids))
       ; return (unitBag abs_bind, poly_ids) }
826
         -- poly_ids are guaranteed zonked by mkExport
827 828

--------------
829
mkExport :: TcPragEnv
830 831
         -> Bool                        -- True <=> there was an insoluble type error
                                        --          when typechecking the bindings
chak@cse.unsw.edu.au.'s avatar
chak@cse.unsw.edu.au. committed
832
         -> [TyVar] -> TcThetaType      -- Both already zonked
Ian Lynagh's avatar
Ian Lynagh committed
833
         -> MonoBindInfo
834
         -> TcM (ABExport GhcTc)
eir@cis.upenn.edu's avatar
eir@cis.upenn.edu committed
835
-- Only called for generalisation plan InferGen, not by CheckGen or NoGen
836 837 838
--
-- mkExport generates exports with
--      zonked type variables,
Ian Lynagh's avatar
Ian Lynagh committed
839
--      zonked poly_ids
840 841 842 843
-- The former is just because no further unifications will change
-- the quantified type variables, so we can fix their final form
-- right now.
-- The latter is needed because the poly_ids are used to extend the
844
-- type environment; see the invariant on TcEnv.tcExtendIdEnv
845

846
-- Pre-condition: the qtvs and theta are already zonked
847

848
mkExport prag_fn insoluble qtvs theta
eir@cis.upenn.edu's avatar
eir@cis.upenn.edu committed
849 850 851
         mono_info@(MBI { mbi_poly_name = poly_name
                        , mbi_sig       = mb_sig
                        , mbi_mono_id   = mono_id })
852
  = do  { mono_ty <- zonkTcType (idType mono_id)
853
        ; poly_id <- mkInferredPolyId insoluble qtvs theta poly_name mb_sig mono_ty
854 855

        -- NB: poly_id has a zonked type
856
        ; poly_id <- addInlinePrags poly_id prag_sigs
857
        ; spec_prags <- tcSpecPrags poly_id prag_sigs
Ian Lynagh's avatar
Ian Lynagh committed
858
                -- tcPrags requires a zonked poly_id
859

Gabor Greif's avatar
Gabor Greif committed
860
        -- See Note [Impedance matching]
861 862
        -- NB: we have already done checkValidType, including an ambiguity check,
        --     on the type; either when we checked the sig or in mkInferredPolyId
863
        ; let poly_ty     = idType poly_id
864
              sel_poly_ty = mkInfSigmaTy qtvs theta mono_ty
865
                -- This type is just going into tcSubType,
866
                -- so Inferred vs. Specified doesn't matter
eir@cis.upenn.edu's avatar
eir@cis.upenn.edu committed
867 868

        ; wrap <- if sel_poly_ty `eqType` poly_ty  -- NB: eqType ignores visibility
869
                  then return idHsWrapper  -- Fast path; also avoids complaint when we infer
870
                                           -- an ambiguous type and have AllowAmbiguousType
871
                                           -- e..g infer  x :: forall a. F a -> Int
Gabor Greif's avatar
Gabor Greif committed
872
                  else addErrCtxtM (mk_impedance_match_msg mono_info sel_poly_ty poly_ty) $
873
                       tcSubType_NC sig_ctxt sel_poly_ty poly_ty
874

manav's avatar
manav committed
875
        ; warn_missing_sigs <- woptM Opt_WarnMissingLocalSignatures
876 877
        ; when warn_missing_sigs $
              localSigWarn Opt_WarnMissingLocalSignatures poly_id mb_sig
878

879 880
        ; return (ABE { abe_ext = noExt
                      , abe_wrap = wrap
881
                        -- abe_wrap :: idType poly_id ~ (forall qtvs. theta => mono_ty)
882 883 884
                      , abe_poly  = poly_id
                      , abe_mono  = mono_id
                      , abe_prags = SpecPrags spec_prags }) }
885
  where
886
    prag_sigs = lookupPragEnv prag_fn poly_name
887
    sig_ctxt  = InfSigCtxt poly_name
888

889 890 891
mkInferredPolyId :: Bool  -- True <=> there was an insoluble error when
                          --          checking the binding group for this Id
                 -> [TyVar] -> TcThetaType
892
                 -> Name -> Maybe TcIdSigInst -> TcType
893
                 -> TcM TcId
894
mkInferredPolyId insoluble qtvs inferred_theta poly_name mb_sig_inst mono_ty
895 896
  | Just (TISI { sig_inst_sig = sig })  <- mb_sig_inst
  , CompleteSig { sig_bndr = poly_id } <- sig
897 898 899 900
  = return poly_id

  | otherwise  -- Either no type sig or partial type sig
  = checkNoErrs $  -- The checkNoErrs ensures that if the type is ambiguous
Gabor Greif's avatar
Gabor Greif committed
901
                   -- we don't carry on to the impedance matching, and generate
902 903 904
                   -- a duplicate ambiguity error.  There is a similar
                   -- checkNoErrs for complete type signatures too.
    do { fam_envs <- tcGetFamInstEnvs
905
       ; let (_co, mono_ty') = normaliseType fam_envs Nominal mono_ty
906 907
               -- Unification may not have normalised the type,
               -- (see Note [Lazy flattening] in TcFlatten) so do it
908 909 910
               -- here to make it as uncomplicated as possible.
               -- Example: f :: [F Int] -> Bool
               -- should be rewritten to f :: [Char] -> Bool, if possible
911
               --
Gabor Greif's avatar
Gabor Greif committed
912
               -- We can discard the coercion _co, because we'll reconstruct
913
               -- it in the call to tcSubType below
914

eir@cis.upenn.edu's avatar
eir@cis.upenn.edu committed
915
       ; (binders, theta') <- chooseInferredQuantifiers inferred_theta
916
                                (tyCoVarsOfType mono_ty') qtvs mb_sig_inst
917

eir@cis.upenn.edu's avatar
eir@cis.upenn.edu committed
918
       ; let inferred_poly_ty = mkForAllTys binders (mkPhiTy theta' mono_ty')
919

eir@cis.upenn.edu's avatar
eir@cis.upenn.edu committed
920
       ; traceTc "mkInferredPolyId" (vcat [ppr poly_name, ppr qtvs, ppr theta'
Simon Peyton Jones's avatar
Simon Peyton Jones committed
921
                                          , ppr inferred_poly_ty])