2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[Main_match]{The @match@ function}
7 module Match ( match, matchEquations, matchWrapper, matchSimply, matchSinglePat ) where
9 #include "HsVersions.h"
11 import DynFlags ( DynFlag(..), dopt )
13 import TcHsSyn ( mkVanillaTuplePat )
14 import Check ( check, ExhaustivePat )
16 import CoreUtils ( bindNonRec, exprType )
18 import DsBinds ( dsLHsBinds )
19 import DsGRHSs ( dsGRHSs )
21 import Id ( idName, idType, Id )
22 import DataCon ( dataConFieldLabels, dataConInstOrigArgTys, isVanillaDataCon )
23 import MatchCon ( matchConFamily )
24 import MatchLit ( matchLiterals, matchNPlusKPats, matchNPats, tidyLitPat, tidyNPat )
25 import PrelInfo ( pAT_ERROR_ID )
26 import TcType ( Type, tcTyConAppArgs )
27 import Type ( splitFunTysN, mkTyVarTys )
28 import TysWiredIn ( consDataCon, mkListTy, unitTy,
29 tupleCon, parrFakeCon, mkPArrTy )
30 import BasicTypes ( Boxity(..) )
31 import ListSetOps ( runs )
32 import SrcLoc ( noLoc, unLoc, Located(..) )
33 import Util ( lengthExceeds, notNull )
38 This function is a wrapper of @match@, it must be called from all the parts where
39 it was called match, but only substitutes the firs call, ....
40 if the associated flags are declared, warnings will be issued.
41 It can not be called matchWrapper because this name already exists :-(
46 matchCheck :: DsMatchContext
47 -> [Id] -- Vars rep'ing the exprs we're matching with
48 -> Type -- Type of the case expression
49 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
50 -> DsM MatchResult -- Desugared result!
52 matchCheck ctx vars ty qs
53 = getDOptsDs `thenDs` \ dflags ->
54 matchCheck_really dflags ctx vars ty qs
56 matchCheck_really dflags ctx vars ty qs
57 | incomplete && shadow =
58 dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
59 dsIncompleteWarn ctx pats `thenDs` \ () ->
62 dsIncompleteWarn ctx pats `thenDs` \ () ->
65 dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
69 where (pats, eqns_shadow) = check qs
70 incomplete = want_incomplete && (notNull pats)
71 want_incomplete = case ctx of
72 DsMatchContext RecUpd _ ->
73 dopt Opt_WarnIncompletePatternsRecUpd dflags
75 dopt Opt_WarnIncompletePatterns dflags
76 shadow = dopt Opt_WarnOverlappingPatterns dflags
77 && not (null eqns_shadow)
80 This variable shows the maximum number of lines of output generated for warnings.
81 It will limit the number of patterns/equations displayed to@ maximum_output@.
83 (ToDo: add command-line option?)
89 The next two functions create the warning message.
92 dsShadowWarn :: DsMatchContext -> [EquationInfo] -> DsM ()
93 dsShadowWarn ctx@(DsMatchContext kind loc) qs
94 = putSrcSpanDs loc (dsWarn warn)
96 warn | qs `lengthExceeds` maximum_output
97 = pp_context ctx (ptext SLIT("are overlapped"))
98 (\ f -> vcat (map (ppr_eqn f kind) (take maximum_output qs)) $$
101 = pp_context ctx (ptext SLIT("are overlapped"))
102 (\ f -> vcat $ map (ppr_eqn f kind) qs)
105 dsIncompleteWarn :: DsMatchContext -> [ExhaustivePat] -> DsM ()
106 dsIncompleteWarn ctx@(DsMatchContext kind loc) pats
107 = putSrcSpanDs loc (dsWarn warn)
109 warn = pp_context ctx (ptext SLIT("are non-exhaustive"))
110 (\f -> hang (ptext SLIT("Patterns not matched:"))
111 4 ((vcat $ map (ppr_incomplete_pats kind)
112 (take maximum_output pats))
115 dots | pats `lengthExceeds` maximum_output = ptext SLIT("...")
118 pp_context (DsMatchContext kind _loc) msg rest_of_msg_fun
119 = vcat [ptext SLIT("Pattern match(es)") <+> msg,
120 sep [ptext SLIT("In") <+> ppr_match <> char ':', nest 4 (rest_of_msg_fun pref)]]
124 FunRhs fun -> (pprMatchContext kind, \ pp -> ppr fun <+> pp)
125 other -> (pprMatchContext kind, \ pp -> pp)
127 ppr_pats pats = sep (map ppr pats)
129 ppr_shadow_pats kind pats
130 = sep [ppr_pats pats, matchSeparator kind, ptext SLIT("...")]
132 ppr_incomplete_pats kind (pats,[]) = ppr_pats pats
133 ppr_incomplete_pats kind (pats,constraints) =
134 sep [ppr_pats pats, ptext SLIT("with"),
135 sep (map ppr_constraint constraints)]
138 ppr_constraint (var,pats) = sep [ppr var, ptext SLIT("`notElem`"), ppr pats]
140 ppr_eqn prefixF kind eqn = prefixF (ppr_shadow_pats kind (eqn_pats eqn))
144 The function @match@ is basically the same as in the Wadler chapter,
145 except it is monadised, to carry around the name supply, info about
148 Notes on @match@'s arguments, assuming $m$ equations and $n$ patterns:
151 A list of $n$ variable names, those variables presumably bound to the
152 $n$ expressions being matched against the $n$ patterns. Using the
153 list of $n$ expressions as the first argument showed no benefit and
157 The second argument, a list giving the ``equation info'' for each of
161 the $n$ patterns for that equation, and
163 a list of Core bindings [@(Id, CoreExpr)@ pairs] to be ``stuck on
164 the front'' of the matching code, as in:
170 and finally: (ToDo: fill in)
172 The right way to think about the ``after-match function'' is that it
173 is an embryonic @CoreExpr@ with a ``hole'' at the end for the
174 final ``else expression''.
177 There is a type synonym, @EquationInfo@, defined in module @DsUtils@.
179 An experiment with re-ordering this information about equations (in
180 particular, having the patterns available in column-major order)
184 A default expression---what to evaluate if the overall pattern-match
185 fails. This expression will (almost?) always be
186 a measly expression @Var@, unless we know it will only be used once
187 (as we do in @glue_success_exprs@).
189 Leaving out this third argument to @match@ (and slamming in lots of
190 @Var "fail"@s) is a positively {\em bad} idea, because it makes it
191 impossible to share the default expressions. (Also, it stands no
192 chance of working in our post-upheaval world of @Locals@.)
194 So, the full type signature:
196 match :: [Id] -- Variables rep'ing the exprs we're matching with
197 -> Type -- Type of the case expression
198 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
199 -> DsM MatchResult -- Desugared result!
202 Note: @match@ is often called via @matchWrapper@ (end of this module),
203 a function that does much of the house-keeping that goes with a call
206 It is also worth mentioning the {\em typical} way a block of equations
207 is desugared with @match@. At each stage, it is the first column of
208 patterns that is examined. The steps carried out are roughly:
211 Tidy the patterns in column~1 with @tidyEqnInfo@ (this may add
212 bindings to the second component of the equation-info):
215 Remove the `as' patterns from column~1.
217 Make all constructor patterns in column~1 into @ConPats@, notably
218 @ListPats@ and @TuplePats@.
220 Handle any irrefutable (or ``twiddle'') @LazyPats@.
223 Now {\em unmix} the equations into {\em blocks} [w/ local function
224 @unmix_eqns@], in which the equations in a block all have variable
225 patterns in column~1, or they all have constructor patterns in ...
226 (see ``the mixture rule'' in SLPJ).
228 Call @matchEqnBlock@ on each block of equations; it will do the
229 appropriate thing for each kind of column-1 pattern, usually ending up
230 in a recursive call to @match@.
233 %************************************************************************
235 %* match: empty rule *
237 %************************************************************************
238 \subsection[Match-empty-rule]{The ``empty rule''}
240 We are a little more paranoid about the ``empty rule'' (SLPJ, p.~87)
241 than the Wadler-chapter code for @match@ (p.~93, first @match@ clause).
242 And gluing the ``success expressions'' together isn't quite so pretty.
245 match [] ty eqns_info
246 = ASSERT( not (null eqns_info) )
247 returnDs (foldr1 combineMatchResults match_results)
249 match_results = [ ASSERT( null (eqn_pats eqn) )
250 adjustMatchResult (eqn_wrap eqn) (eqn_rhs eqn)
255 %************************************************************************
257 %* match: non-empty rule *
259 %************************************************************************
260 \subsection[Match-nonempty]{@match@ when non-empty: unmixing}
262 This (more interesting) clause of @match@ uses @tidy_and_unmix_eqns@
263 (a)~to get `as'- and `twiddle'-patterns out of the way (tidying), and
264 (b)~to do ``the mixture rule'' (SLPJ, p.~88) [which really {\em
265 un}mixes the equations], producing a list of equation-info
266 blocks, each block having as its first column of patterns either all
267 constructors, or all variables (or similar beasts), etc.
269 @match_unmixed_eqn_blks@ simply takes the place of the @foldr@ in the
270 Wadler-chapter @match@ (p.~93, last clause), and @match_unmixed_blk@
271 corresponds roughly to @matchVarCon@.
274 match vars@(v:_) ty eqns_info
275 = do { tidy_eqns <- mappM (tidyEqnInfo v) eqns_info
276 ; let eqns_blks = runs same_family tidy_eqns
277 ; match_results <- mappM match_block eqns_blks
278 ; ASSERT( not (null match_results) )
279 return (foldr1 combineMatchResults match_results) }
281 same_family eqn1 eqn2
282 = samePatFamily (firstPat eqn1) (firstPat eqn2)
285 = case firstPat (head eqns) of
286 WildPat {} -> matchVariables vars ty eqns
287 ConPatOut {} -> matchConFamily vars ty eqns
288 NPlusKPat {} -> matchNPlusKPats vars ty eqns
289 NPat {} -> matchNPats vars ty eqns
290 LitPat {} -> matchLiterals vars ty eqns
292 -- After tidying, there are only five kinds of patterns
293 samePatFamily (WildPat {}) (WildPat {}) = True
294 samePatFamily (ConPatOut {}) (ConPatOut {}) = True
295 samePatFamily (NPlusKPat {}) (NPlusKPat {}) = True
296 samePatFamily (NPat {}) (NPat {}) = True
297 samePatFamily (LitPat {}) (LitPat {}) = True
298 samePatFamily _ _ = False
300 matchVariables :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
301 -- Real true variables, just like in matchVar, SLPJ p 94
302 -- No binding to do: they'll all be wildcards by now (done in tidy)
303 matchVariables (var:vars) ty eqns = match vars ty (shiftEqns eqns)
309 Tidy up the leftmost pattern in an @EquationInfo@, given the variable @v@
310 which will be scrutinised. This means:
313 Replace variable patterns @x@ (@x /= v@) with the pattern @_@,
314 together with the binding @x = v@.
316 Replace the `as' pattern @x@@p@ with the pattern p and a binding @x = v@.
318 Removing lazy (irrefutable) patterns (you don't want to know...).
320 Converting explicit tuple-, list-, and parallel-array-pats into ordinary
323 Convert the literal pat "" to [].
326 The result of this tidying is that the column of patterns will include
330 The @VarPat@ information isn't needed any more after this.
333 @ListPats@, @TuplePats@, etc., are all converted into @ConPats@.
335 \item[@LitPats@ and @NPats@:]
336 @LitPats@/@NPats@ of ``known friendly types'' (Int, Char,
337 Float, Double, at least) are converted to unboxed form; e.g.,
338 \tr{(NPat (HsInt i) _ _)} is converted to:
340 (ConPat I# _ _ [LitPat (HsIntPrim i)])
345 tidyEqnInfo :: Id -> EquationInfo -> DsM EquationInfo
346 -- DsM'd because of internal call to dsLHsBinds
347 -- and mkSelectorBinds.
348 -- "tidy1" does the interesting stuff, looking at
349 -- one pattern and fiddling the list of bindings.
351 -- POST CONDITION: head pattern in the EqnInfo is
359 tidyEqnInfo v eqn@(EqnInfo { eqn_wrap = wrap, eqn_pats = pat : pats })
360 = tidy1 v wrap pat `thenDs` \ (wrap', pat') ->
361 returnDs (eqn { eqn_wrap = wrap', eqn_pats = pat' : pats })
363 tidy1 :: Id -- The Id being scrutinised
364 -> DsWrapper -- Previous wrapping bindings
365 -> Pat Id -- The pattern against which it is to be matched
366 -> DsM (DsWrapper, -- Extra bindings around what to do afterwards
367 Pat Id) -- Equivalent pattern
369 -- The extra bindings etc are all wrapped around the RHS of the match
370 -- so they are only available when matching is complete. But that's ok
371 -- becuase, for example, in the pattern x@(...), the x can only be
372 -- used in the RHS, not in the nested pattern, nor subsquent patterns
374 -- However this does have an awkward consequence. The bindings in
375 -- a VarPatOut get wrapped around the result in right to left order,
376 -- rather than left to right. This only matters if one set of
377 -- bindings can mention things used in another, and that can happen
378 -- if we allow equality dictionary bindings of form d1=d2.
379 -- bindIInstsOfLocalFuns is now careful not to do this, but it's a wart.
380 -- (Without this care in bindInstsOfLocalFuns, compiling
381 -- Data.Generics.Schemes.hs fails in function everywhereBut.)
383 -------------------------------------------------------
384 -- (pat', mr') = tidy1 v pat mr
385 -- tidies the *outer level only* of pat, giving pat'
386 -- It eliminates many pattern forms (as-patterns, variable patterns,
387 -- list patterns, etc) yielding one of:
394 tidy1 v wrap (ParPat pat) = tidy1 v wrap (unLoc pat)
395 tidy1 v wrap (SigPatOut pat _) = tidy1 v wrap (unLoc pat)
396 tidy1 v wrap (WildPat ty) = returnDs (wrap, WildPat ty)
398 -- case v of { x -> mr[] }
399 -- = case v of { _ -> let x=v in mr[] }
400 tidy1 v wrap (VarPat var)
401 = returnDs (wrap . wrapBind var v, WildPat (idType var))
403 tidy1 v wrap (VarPatOut var binds)
404 = do { prs <- dsLHsBinds binds
405 ; return (wrap . wrapBind var v . mkDsLet (Rec prs),
406 WildPat (idType var)) }
408 -- case v of { x@p -> mr[] }
409 -- = case v of { p -> let x=v in mr[] }
410 tidy1 v wrap (AsPat (L _ var) pat)
411 = tidy1 v (wrap . wrapBind var v) (unLoc pat)
413 tidy1 v wrap (BangPat pat)
414 = tidy1 v (wrap . seqVar v) (unLoc pat)
416 {- now, here we handle lazy patterns:
417 tidy1 v ~p bs = (v, v1 = case v of p -> v1 :
418 v2 = case v of p -> v2 : ... : bs )
420 where the v_i's are the binders in the pattern.
422 ToDo: in "v_i = ... -> v_i", are the v_i's really the same thing?
424 The case expr for v_i is just: match [v] [(p, [], \ x -> Var v_i)] any_expr
427 tidy1 v wrap (LazyPat pat)
428 = do { v' <- newSysLocalDs (idType v)
429 ; sel_prs <- mkSelectorBinds pat (Var v)
430 ; let sel_binds = [NonRec b rhs | (b,rhs) <- sel_prs]
431 ; returnDs (wrap . wrapBind v' v . mkDsLets sel_binds,
432 WildPat (idType v)) }
434 -- re-express <con-something> as (ConPat ...) [directly]
436 tidy1 v wrap (ConPatOut (L loc con) ex_tvs dicts binds ps pat_ty)
437 = returnDs (wrap, ConPatOut (L loc con) ex_tvs dicts binds tidy_ps pat_ty)
439 tidy_ps = PrefixCon (tidy_con con ex_tvs pat_ty ps)
441 tidy1 v wrap (ListPat pats ty)
442 = returnDs (wrap, unLoc list_ConPat)
444 list_ty = mkListTy ty
445 list_ConPat = foldr (\ x y -> mkPrefixConPat consDataCon [x, y] list_ty)
449 -- Introduce fake parallel array constructors to be able to handle parallel
450 -- arrays with the existing machinery for constructor pattern
451 tidy1 v wrap (PArrPat pats ty)
452 = returnDs (wrap, unLoc parrConPat)
455 parrConPat = mkPrefixConPat (parrFakeCon arity) pats (mkPArrTy ty)
457 tidy1 v wrap (TuplePat pats boxity ty)
458 = returnDs (wrap, unLoc tuple_ConPat)
461 tuple_ConPat = mkPrefixConPat (tupleCon boxity arity) pats ty
463 tidy1 v wrap (DictPat dicts methods)
464 = case num_of_d_and_ms of
465 0 -> tidy1 v wrap (TuplePat [] Boxed unitTy)
466 1 -> tidy1 v wrap (unLoc (head dict_and_method_pats))
467 _ -> tidy1 v wrap (mkVanillaTuplePat dict_and_method_pats Boxed)
469 num_of_d_and_ms = length dicts + length methods
470 dict_and_method_pats = map nlVarPat (dicts ++ methods)
472 -- LitPats: we *might* be able to replace these w/ a simpler form
473 tidy1 v wrap pat@(LitPat lit)
474 = returnDs (wrap, unLoc (tidyLitPat lit (noLoc pat)))
476 -- NPats: we *might* be able to replace these w/ a simpler form
477 tidy1 v wrap pat@(NPat lit mb_neg _ lit_ty)
478 = returnDs (wrap, unLoc (tidyNPat lit mb_neg lit_ty (noLoc pat)))
480 -- and everything else goes through unchanged...
482 tidy1 v wrap non_interesting_pat
483 = returnDs (wrap, non_interesting_pat)
486 tidy_con data_con ex_tvs pat_ty (PrefixCon ps) = ps
487 tidy_con data_con ex_tvs pat_ty (InfixCon p1 p2) = [p1,p2]
488 tidy_con data_con ex_tvs pat_ty (RecCon rpats)
490 = -- Special case for C {}, which can be used for
491 -- a constructor that isn't declared to have
493 map (noLoc . WildPat) con_arg_tys'
496 = map mk_pat tagged_arg_tys
498 -- Boring stuff to find the arg-tys of the constructor
500 inst_tys | isVanillaDataCon data_con = tcTyConAppArgs pat_ty -- Newtypes must be opaque
501 | otherwise = mkTyVarTys ex_tvs
503 con_arg_tys' = dataConInstOrigArgTys data_con inst_tys
504 tagged_arg_tys = con_arg_tys' `zip` dataConFieldLabels data_con
506 -- mk_pat picks a WildPat of the appropriate type for absent fields,
507 -- and the specified pattern for present fields
508 mk_pat (arg_ty, lbl) =
509 case [ pat | (sel_id,pat) <- rpats, idName (unLoc sel_id) == lbl] of
510 (pat:pats) -> ASSERT( null pats ) pat
511 [] -> noLoc (WildPat arg_ty)
515 {\bf Previous @matchTwiddled@ stuff:}
517 Now we get to the only interesting part; note: there are choices for
518 translation [from Simon's notes]; translation~1:
525 s = case w of [s,t] -> s
526 t = case w of [s,t] -> t
530 Here \tr{w} is a fresh variable, and the \tr{w}-binding prevents multiple
531 evaluation of \tr{e}. An alternative translation (No.~2):
533 [ w = case e of [s,t] -> (s,t)
534 s = case w of (s,t) -> s
535 t = case w of (s,t) -> t
539 %************************************************************************
541 \subsubsection[improved-unmixing]{UNIMPLEMENTED idea for improved unmixing}
543 %************************************************************************
545 We might be able to optimise unmixing when confronted by
546 only-one-constructor-possible, of which tuples are the most notable
554 This definition would normally be unmixed into four equation blocks,
555 one per equation. But it could be unmixed into just one equation
556 block, because if the one equation matches (on the first column),
557 the others certainly will.
559 You have to be careful, though; the example
567 {\em must} be broken into two blocks at the line shown; otherwise, you
568 are forcing unnecessary evaluation. In any case, the top-left pattern
569 always gives the cue. You could then unmix blocks into groups of...
571 \item[all variables:]
573 \item[constructors or variables (mixed):]
574 Need to make sure the right names get bound for the variable patterns.
575 \item[literals or variables (mixed):]
576 Presumably just a variant on the constructor case (as it is now).
579 %************************************************************************
581 %* matchWrapper: a convenient way to call @match@ *
583 %************************************************************************
584 \subsection[matchWrapper]{@matchWrapper@: a convenient interface to @match@}
586 Calls to @match@ often involve similar (non-trivial) work; that work
587 is collected here, in @matchWrapper@. This function takes as
591 Typchecked @Matches@ (of a function definition, or a case or lambda
592 expression)---the main input;
594 An error message to be inserted into any (runtime) pattern-matching
598 As results, @matchWrapper@ produces:
601 A list of variables (@Locals@) that the caller must ``promise'' to
602 bind to appropriate values; and
604 a @CoreExpr@, the desugared output (main result).
607 The main actions of @matchWrapper@ include:
610 Flatten the @[TypecheckedMatch]@ into a suitable list of
613 Create as many new variables as there are patterns in a pattern-list
614 (in any one of the @EquationInfo@s).
616 Create a suitable ``if it fails'' expression---a call to @error@ using
617 the error-string input; the {\em type} of this fail value can be found
618 by examining one of the RHS expressions in one of the @EquationInfo@s.
620 Call @match@ with all of this information!
624 matchWrapper :: HsMatchContext Name -- For shadowing warning messages
625 -> MatchGroup Id -- Matches being desugared
626 -> DsM ([Id], CoreExpr) -- Results
629 There is one small problem with the Lambda Patterns, when somebody
630 writes something similar to:
634 he/she don't want a warning about incomplete patterns, that is done with
635 the flag @opt_WarnSimplePatterns@.
636 This problem also appears in the:
638 \item @do@ patterns, but if the @do@ can fail
639 it creates another equation if the match can fail
640 (see @DsExpr.doDo@ function)
641 \item @let@ patterns, are treated by @matchSimply@
642 List Comprension Patterns, are treated by @matchSimply@ also
645 We can't call @matchSimply@ with Lambda patterns,
646 due to the fact that lambda patterns can have more than
647 one pattern, and match simply only accepts one pattern.
652 matchWrapper ctxt (MatchGroup matches match_ty)
653 = do { eqns_info <- mapM mk_eqn_info matches
654 ; new_vars <- selectMatchVars arg_pats pat_tys
655 ; result_expr <- matchEquations ctxt new_vars eqns_info rhs_ty
656 ; return (new_vars, result_expr) }
658 arg_pats = map unLoc (hsLMatchPats (head matches))
659 n_pats = length arg_pats
660 (pat_tys, rhs_ty) = splitFunTysN n_pats match_ty
662 mk_eqn_info (L _ (Match pats _ grhss))
663 = do { let upats = map unLoc pats
664 ; match_result <- dsGRHSs ctxt upats grhss rhs_ty
665 ; return (EqnInfo { eqn_wrap = idWrapper,
667 eqn_rhs = match_result}) }
670 matchEquations :: HsMatchContext Name
671 -> [Id] -> [EquationInfo] -> Type
673 matchEquations ctxt vars eqns_info rhs_ty
674 = do { dflags <- getDOptsDs
675 ; locn <- getSrcSpanDs
676 ; let ds_ctxt = DsMatchContext ctxt locn
677 error_string = matchContextErrString ctxt
679 ; match_result <- match_fun dflags ds_ctxt vars rhs_ty eqns_info
681 ; fail_expr <- mkErrorAppDs pAT_ERROR_ID rhs_ty error_string
682 ; extractMatchResult match_result fail_expr }
684 match_fun dflags ds_ctxt
686 LambdaExpr | dopt Opt_WarnSimplePatterns dflags -> matchCheck ds_ctxt
688 _ -> matchCheck ds_ctxt
691 %************************************************************************
693 \subsection[matchSimply]{@matchSimply@: match a single expression against a single pattern}
695 %************************************************************************
697 @mkSimpleMatch@ is a wrapper for @match@ which deals with the
698 situation where we want to match a single expression against a single
699 pattern. It returns an expression.
702 matchSimply :: CoreExpr -- Scrutinee
703 -> HsMatchContext Name -- Match kind
704 -> LPat Id -- Pattern it should match
705 -> CoreExpr -- Return this if it matches
706 -> CoreExpr -- Return this if it doesn't
709 matchSimply scrut hs_ctx pat result_expr fail_expr
711 match_result = cantFailMatchResult result_expr
712 rhs_ty = exprType fail_expr
713 -- Use exprType of fail_expr, because won't refine in the case of failure!
715 matchSinglePat scrut hs_ctx pat rhs_ty match_result `thenDs` \ match_result' ->
716 extractMatchResult match_result' fail_expr
719 matchSinglePat :: CoreExpr -> HsMatchContext Name -> LPat Id
720 -> Type -> MatchResult -> DsM MatchResult
721 matchSinglePat (Var var) hs_ctx (L _ pat) ty match_result
722 = getDOptsDs `thenDs` \ dflags ->
723 getSrcSpanDs `thenDs` \ locn ->
726 | dopt Opt_WarnSimplePatterns dflags = matchCheck ds_ctx
729 ds_ctx = DsMatchContext hs_ctx locn
731 match_fn dflags [var] ty [EqnInfo { eqn_wrap = idWrapper,
733 eqn_rhs = match_result }]
735 matchSinglePat scrut hs_ctx pat ty match_result
736 = selectSimpleMatchVarL pat `thenDs` \ var ->
737 matchSinglePat (Var var) hs_ctx pat ty match_result `thenDs` \ match_result' ->
738 returnDs (adjustMatchResult (bindNonRec var scrut) match_result')