2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utilities for desugaring
8 This module exports some utility functions of no great interest.
12 -- | Utility functions for constructing Core syntax, principally for desugaring
17 MatchResult(..), CanItFail(..),
18 cantFailMatchResult, alwaysFailMatchResult,
19 extractMatchResult, combineMatchResults,
20 adjustMatchResult, adjustMatchResultDs,
21 mkCoLetMatchResult, mkViewMatchResult, mkGuardedMatchResult,
22 matchCanFail, mkEvalMatchResult,
23 mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult,
31 mkLHsVarTup, mkLHsTup, mkLHsVarPatTup, mkLHsPatTup,
32 mkBigLHsVarTup, mkBigLHsTup, mkBigLHsVarPatTup, mkBigLHsPatTup,
36 dsSyntaxTable, lookupEvidence,
38 selectSimpleMatchVarL, selectMatchVars, selectMatchVar,
39 mkTickBox, mkOptTickBox, mkBinaryTickBox
42 #include "HsVersions.h"
44 import {-# SOURCE #-} Match ( matchSimply )
45 import {-# SOURCE #-} DsExpr( dsExpr )
49 import TcType( tcSplitTyConApp )
80 %************************************************************************
84 %************************************************************************
87 dsSyntaxTable :: SyntaxTable Id
88 -> DsM ([CoreBind], -- Auxiliary bindings
89 [(Name,Id)]) -- Maps the standard name to its value
91 dsSyntaxTable rebound_ids = do
92 (binds_s, prs) <- mapAndUnzipM mk_bind rebound_ids
93 return (concat binds_s, prs)
95 -- The cheapo special case can happen when we
96 -- make an intermediate HsDo when desugaring a RecStmt
97 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
98 mk_bind (std_name, expr) = do
100 id <- newSysLocalDs (exprType rhs)
101 return ([NonRec id rhs], (std_name, id))
103 lookupEvidence :: [(Name, Id)] -> Name -> Id
104 lookupEvidence prs std_name
105 = assocDefault (mk_panic std_name) prs std_name
107 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext (sLit "Not found:") <+> ppr std_name)
110 %************************************************************************
112 \subsection{ Selecting match variables}
114 %************************************************************************
116 We're about to match against some patterns. We want to make some
117 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
118 hand, which should indeed be bound to the pattern as a whole, then use it;
119 otherwise, make one up.
122 selectSimpleMatchVarL :: LPat Id -> DsM Id
123 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
125 -- (selectMatchVars ps tys) chooses variables of type tys
126 -- to use for matching ps against. If the pattern is a variable,
127 -- we try to use that, to save inventing lots of fresh variables.
129 -- OLD, but interesting note:
130 -- But even if it is a variable, its type might not match. Consider
132 -- T1 :: Int -> T Int
135 -- f :: T a -> a -> Int
136 -- f (T1 i) (x::Int) = x
137 -- f (T2 i) (y::a) = 0
138 -- Then we must not choose (x::Int) as the matching variable!
139 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
141 selectMatchVars :: [Pat Id] -> DsM [Id]
142 selectMatchVars ps = mapM selectMatchVar ps
144 selectMatchVar :: Pat Id -> DsM Id
145 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
146 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
147 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
148 selectMatchVar (VarPat var) = return var
149 selectMatchVar (AsPat var _) = return (unLoc var)
150 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
151 -- OK, better make up one...
155 %************************************************************************
157 %* type synonym EquationInfo and access functions for its pieces *
159 %************************************************************************
160 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
162 The ``equation info'' used by @match@ is relatively complicated and
163 worthy of a type synonym and a few handy functions.
166 firstPat :: EquationInfo -> Pat Id
167 firstPat eqn = ASSERT( notNull (eqn_pats eqn) ) head (eqn_pats eqn)
169 shiftEqns :: [EquationInfo] -> [EquationInfo]
170 -- Drop the first pattern in each equation
171 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
174 Functions on MatchResults
177 matchCanFail :: MatchResult -> Bool
178 matchCanFail (MatchResult CanFail _) = True
179 matchCanFail (MatchResult CantFail _) = False
181 alwaysFailMatchResult :: MatchResult
182 alwaysFailMatchResult = MatchResult CanFail (\fail -> return fail)
184 cantFailMatchResult :: CoreExpr -> MatchResult
185 cantFailMatchResult expr = MatchResult CantFail (\_ -> return expr)
187 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
188 extractMatchResult (MatchResult CantFail match_fn) _
189 = match_fn (error "It can't fail!")
191 extractMatchResult (MatchResult CanFail match_fn) fail_expr = do
192 (fail_bind, if_it_fails) <- mkFailurePair fail_expr
193 body <- match_fn if_it_fails
194 return (mkCoreLet fail_bind body)
197 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
198 combineMatchResults (MatchResult CanFail body_fn1)
199 (MatchResult can_it_fail2 body_fn2)
200 = MatchResult can_it_fail2 body_fn
202 body_fn fail = do body2 <- body_fn2 fail
203 (fail_bind, duplicatable_expr) <- mkFailurePair body2
204 body1 <- body_fn1 duplicatable_expr
205 return (Let fail_bind body1)
207 combineMatchResults match_result1@(MatchResult CantFail _) _
210 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
211 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
212 = MatchResult can_it_fail (\fail -> encl_fn <$> body_fn fail)
214 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
215 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
216 = MatchResult can_it_fail (\fail -> encl_fn =<< body_fn fail)
218 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
220 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
222 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
223 wrapBind new old body -- Can deal with term variables *or* type variables
225 | isTyVar new = Let (mkTyBind new (mkTyVarTy old)) body
226 | otherwise = Let (NonRec new (Var old)) body
228 seqVar :: Var -> CoreExpr -> CoreExpr
229 seqVar var body = Case (Var var) var (exprType body)
230 [(DEFAULT, [], body)]
232 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
233 mkCoLetMatchResult bind = adjustMatchResult (mkCoreLet bind)
235 -- (mkViewMatchResult var' viewExpr var mr) makes the expression
236 -- let var' = viewExpr var in mr
237 mkViewMatchResult :: Id -> CoreExpr -> Id -> MatchResult -> MatchResult
238 mkViewMatchResult var' viewExpr var =
239 adjustMatchResult (mkCoreLet (NonRec var' (mkCoreApp viewExpr (Var var))))
241 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
242 mkEvalMatchResult var ty
243 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
245 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
246 mkGuardedMatchResult pred_expr (MatchResult _ body_fn)
247 = MatchResult CanFail (\fail -> do body <- body_fn fail
248 return (mkIfThenElse pred_expr body fail))
250 mkCoPrimCaseMatchResult :: Id -- Scrutinee
251 -> Type -- Type of the case
252 -> [(Literal, MatchResult)] -- Alternatives
254 mkCoPrimCaseMatchResult var ty match_alts
255 = MatchResult CanFail mk_case
258 alts <- mapM (mk_alt fail) sorted_alts
259 return (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
261 sorted_alts = sortWith fst match_alts -- Right order for a Case
262 mk_alt fail (lit, MatchResult _ body_fn) = do body <- body_fn fail
263 return (LitAlt lit, [], body)
266 mkCoAlgCaseMatchResult :: Id -- Scrutinee
267 -> Type -- Type of exp
268 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
270 mkCoAlgCaseMatchResult var ty match_alts
271 | isNewTyCon tycon -- Newtype case; use a let
272 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
273 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
275 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
276 = MatchResult CanFail mk_parrCase
278 | otherwise -- Datatype case; use a case
279 = MatchResult fail_flag mk_case
281 tycon = dataConTyCon con1
282 -- [Interesting: becuase of GADTs, we can't rely on the type of
283 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
286 (con1, arg_ids1, match_result1) = ASSERT( notNull match_alts ) head match_alts
287 arg_id1 = ASSERT( notNull arg_ids1 ) head arg_ids1
289 (tc, ty_args) = tcSplitTyConApp var_ty -- Don't look through newtypes
290 -- (not that splitTyConApp does, these days)
291 newtype_rhs = unwrapNewTypeBody tc ty_args (Var var)
293 -- Stuff for data types
294 data_cons = tyConDataCons tycon
295 match_results = [match_result | (_,_,match_result) <- match_alts]
297 fail_flag | exhaustive_case
298 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
302 sorted_alts = sortWith get_tag match_alts
303 get_tag (con, _, _) = dataConTag con
304 mk_case fail = do alts <- mapM (mk_alt fail) sorted_alts
305 return (mkWildCase (Var var) (idType var) ty (mk_default fail ++ alts))
307 mk_alt fail (con, args, MatchResult _ body_fn) = do
309 us <- newUniqueSupply
310 return (mkReboxingAlt (uniqsFromSupply us) con args body)
312 mk_default fail | exhaustive_case = []
313 | otherwise = [(DEFAULT, [], fail)]
315 un_mentioned_constructors
316 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
317 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
319 -- Stuff for parallel arrays
321 -- * the following is to desugar cases over fake constructors for
322 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
325 -- Concerning `isPArrFakeAlts':
327 -- * it is *not* sufficient to just check the type of the type
328 -- constructor, as we have to be careful not to confuse the real
329 -- representation of parallel arrays with the fake constructors;
330 -- moreover, a list of alternatives must not mix fake and real
331 -- constructors (this is checked earlier on)
333 -- FIXME: We actually go through the whole list and make sure that
334 -- either all or none of the constructors are fake parallel
335 -- array constructors. This is to spot equations that mix fake
336 -- constructors with the real representation defined in
337 -- `PrelPArr'. It would be nicer to spot this situation
338 -- earlier and raise a proper error message, but it can really
339 -- only happen in `PrelPArr' anyway.
341 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
342 isPArrFakeAlts ((dcon, _, _):alts) =
343 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
344 (True , True ) -> True
345 (False, False) -> False
346 _ -> panic "DsUtils: you may not mix `[:...:]' with `PArr' patterns"
347 isPArrFakeAlts [] = panic "DsUtils: unexpectedly found an empty list of PArr fake alternatives"
349 mk_parrCase fail = do
350 lengthP <- dsLookupGlobalId lengthPName
352 return (mkWildCase (len lengthP) intTy ty [alt])
354 elemTy = case splitTyConApp (idType var) of
355 (_, [elemTy]) -> elemTy
357 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
358 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
361 l <- newSysLocalDs intPrimTy
362 indexP <- dsLookupGlobalId indexPName
363 alts <- mapM (mkAlt indexP) sorted_alts
364 return (DataAlt intDataCon, [l], mkWildCase (Var l) intPrimTy ty (dft : alts))
366 dft = (DEFAULT, [], fail)
368 -- each alternative matches one array length (corresponding to one
369 -- fake array constructor), so the match is on a literal; each
370 -- alternative's body is extended by a local binding for each
371 -- constructor argument, which are bound to array elements starting
374 mkAlt indexP (con, args, MatchResult _ bodyFun) = do
376 return (LitAlt lit, [], mkCoreLets binds body)
378 lit = MachInt $ toInteger (dataConSourceArity con)
379 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
381 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
384 %************************************************************************
386 \subsection{Desugarer's versions of some Core functions}
388 %************************************************************************
391 mkErrorAppDs :: Id -- The error function
392 -> Type -- Type to which it should be applied
393 -> SDoc -- The error message string to pass
396 mkErrorAppDs err_id ty msg = do
397 src_loc <- getSrcSpanDs
399 full_msg = showSDoc (hcat [ppr src_loc, text "|", msg])
400 core_msg = Lit (mkMachString full_msg)
401 -- mkMachString returns a result of type String#
402 return (mkApps (Var err_id) [Type ty, core_msg])
405 %************************************************************************
407 \subsection[mkSelectorBind]{Make a selector bind}
409 %************************************************************************
411 This is used in various places to do with lazy patterns.
412 For each binder $b$ in the pattern, we create a binding:
414 b = case v of pat' -> b'
416 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
418 ToDo: making these bindings should really depend on whether there's
419 much work to be done per binding. If the pattern is complex, it
420 should be de-mangled once, into a tuple (and then selected from).
421 Otherwise the demangling can be in-line in the bindings (as here).
423 Boring! Boring! One error message per binder. The above ToDo is
424 even more helpful. Something very similar happens for pattern-bound
428 mkSelectorBinds :: LPat Id -- The pattern
429 -> CoreExpr -- Expression to which the pattern is bound
430 -> DsM [(Id,CoreExpr)]
432 mkSelectorBinds (L _ (VarPat v)) val_expr
433 = return [(v, val_expr)]
435 mkSelectorBinds pat val_expr
436 | isSingleton binders || is_simple_lpat pat = do
437 -- Given p = e, where p binds x,y
438 -- we are going to make
439 -- v = p (where v is fresh)
440 -- x = case v of p -> x
441 -- y = case v of p -> x
444 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
445 -- This does not matter after desugaring, but there's a subtle
446 -- issue with implicit parameters. Consider
448 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
449 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
450 -- does it get that type? So that when we abstract over it we get the
451 -- right top-level type (?i::Int) => ...)
453 -- So to get the type of 'v', use the pattern not the rhs. Often more
455 val_var <- newSysLocalDs (hsLPatType pat)
457 -- For the error message we make one error-app, to avoid duplication.
458 -- But we need it at different types... so we use coerce for that
459 err_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID unitTy (ppr pat)
460 err_var <- newSysLocalDs unitTy
461 binds <- mapM (mk_bind val_var err_var) binders
462 return ( (val_var, val_expr) :
463 (err_var, err_expr) :
468 error_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID tuple_ty (ppr pat)
469 tuple_expr <- matchSimply val_expr PatBindRhs pat local_tuple error_expr
470 tuple_var <- newSysLocalDs tuple_ty
473 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
474 return ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
476 binders = collectPatBinders pat
477 local_tuple = mkBigCoreVarTup binders
478 tuple_ty = exprType local_tuple
480 mk_bind scrut_var err_var bndr_var = do
481 -- (mk_bind sv err_var) generates
482 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
483 -- Remember, pat binds bv
484 rhs_expr <- matchSimply (Var scrut_var) PatBindRhs pat
485 (Var bndr_var) error_expr
486 return (bndr_var, rhs_expr)
488 error_expr = mkCoerce co (Var err_var)
489 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
491 is_simple_lpat p = is_simple_pat (unLoc p)
493 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
494 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConPatArgs ps)
495 is_simple_pat (VarPat _) = True
496 is_simple_pat (ParPat p) = is_simple_lpat p
497 is_simple_pat _ = False
499 is_triv_lpat p = is_triv_pat (unLoc p)
501 is_triv_pat (VarPat _) = True
502 is_triv_pat (WildPat _) = True
503 is_triv_pat (ParPat p) = is_triv_lpat p
504 is_triv_pat _ = False
508 Creating tuples and their types for full Haskell expressions
512 -- Smart constructors for source tuple expressions
513 mkLHsVarTup :: [Id] -> LHsExpr Id
514 mkLHsVarTup ids = mkLHsTup (map nlHsVar ids)
516 mkLHsTup :: [LHsExpr Id] -> LHsExpr Id
517 mkLHsTup [] = nlHsVar unitDataConId
518 mkLHsTup [lexp] = lexp
519 mkLHsTup lexps = L (getLoc (head lexps)) $
520 ExplicitTuple lexps Boxed
522 -- Smart constructors for source tuple patterns
523 mkLHsVarPatTup :: [Id] -> LPat Id
524 mkLHsVarPatTup bs = mkLHsPatTup (map nlVarPat bs)
526 mkLHsPatTup :: [LPat Id] -> LPat Id
527 mkLHsPatTup [] = noLoc $ mkVanillaTuplePat [] Boxed
528 mkLHsPatTup [lpat] = lpat
529 mkLHsPatTup lpats = L (getLoc (head lpats)) $
530 mkVanillaTuplePat lpats Boxed
532 -- The Big equivalents for the source tuple expressions
533 mkBigLHsVarTup :: [Id] -> LHsExpr Id
534 mkBigLHsVarTup ids = mkBigLHsTup (map nlHsVar ids)
536 mkBigLHsTup :: [LHsExpr Id] -> LHsExpr Id
537 mkBigLHsTup = mkChunkified mkLHsTup
540 -- The Big equivalents for the source tuple patterns
541 mkBigLHsVarPatTup :: [Id] -> LPat Id
542 mkBigLHsVarPatTup bs = mkBigLHsPatTup (map nlVarPat bs)
544 mkBigLHsPatTup :: [LPat Id] -> LPat Id
545 mkBigLHsPatTup = mkChunkified mkLHsPatTup
548 %************************************************************************
550 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
552 %************************************************************************
554 Generally, we handle pattern matching failure like this: let-bind a
555 fail-variable, and use that variable if the thing fails:
557 let fail.33 = error "Help"
568 If the case can't fail, then there'll be no mention of @fail.33@, and the
569 simplifier will later discard it.
572 If it can fail in only one way, then the simplifier will inline it.
575 Only if it is used more than once will the let-binding remain.
578 There's a problem when the result of the case expression is of
579 unboxed type. Then the type of @fail.33@ is unboxed too, and
580 there is every chance that someone will change the let into a case:
586 which is of course utterly wrong. Rather than drop the condition that
587 only boxed types can be let-bound, we just turn the fail into a function
588 for the primitive case:
590 let fail.33 :: Void -> Int#
591 fail.33 = \_ -> error "Help"
600 Now @fail.33@ is a function, so it can be let-bound.
603 mkFailurePair :: CoreExpr -- Result type of the whole case expression
604 -> DsM (CoreBind, -- Binds the newly-created fail variable
605 -- to either the expression or \ _ -> expression
606 CoreExpr) -- Either the fail variable, or fail variable
607 -- applied to unit tuple
609 | isUnLiftedType ty = do
610 fail_fun_var <- newFailLocalDs (unitTy `mkFunTy` ty)
611 fail_fun_arg <- newSysLocalDs unitTy
612 return (NonRec fail_fun_var (Lam fail_fun_arg expr),
613 App (Var fail_fun_var) (Var unitDataConId))
616 fail_var <- newFailLocalDs ty
617 return (NonRec fail_var expr, Var fail_var)
623 mkOptTickBox :: Maybe (Int,[Id]) -> CoreExpr -> DsM CoreExpr
624 mkOptTickBox Nothing e = return e
625 mkOptTickBox (Just (ix,ids)) e = mkTickBox ix ids e
627 mkTickBox :: Int -> [Id] -> CoreExpr -> DsM CoreExpr
628 mkTickBox ix vars e = do
631 let tick | opt_Hpc = mkTickBoxOpId uq mod ix
632 | otherwise = mkBreakPointOpId uq mod ix
634 let occName = mkVarOcc "tick"
635 let name = mkInternalName uq2 occName noSrcSpan -- use mkSysLocal?
636 let var = Id.mkLocalId name realWorldStatePrimTy
639 then return (Var tick)
641 let tickVar = Var tick
642 let tickType = mkFunTys (map idType vars) realWorldStatePrimTy
643 let scrutApTy = App tickVar (Type tickType)
644 return (mkApps scrutApTy (map Var vars) :: Expr Id)
645 return $ Case scrut var ty [(DEFAULT,[],e)]
649 mkBinaryTickBox :: Int -> Int -> CoreExpr -> DsM CoreExpr
650 mkBinaryTickBox ixT ixF e = do
652 let bndr1 = mkSysLocal (fsLit "t1") uq boolTy
653 falseBox <- mkTickBox ixF [] $ Var falseDataConId
654 trueBox <- mkTickBox ixT [] $ Var trueDataConId
655 return $ Case e bndr1 boolTy
656 [ (DataAlt falseDataCon, [], falseBox)
657 , (DataAlt trueDataCon, [], trueBox)