2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[Main_match]{The @match@ function}
7 module Match ( match, matchExport, matchWrapper, matchSimply, matchSinglePat ) where
9 #include "HsVersions.h"
11 import {-# SOURCE #-} DsExpr ( dsExpr, dsLet )
13 import CmdLineOpts ( opt_WarnIncompletePatterns, opt_WarnOverlappingPatterns,
14 opt_WarnSimplePatterns
17 import TcHsSyn ( TypecheckedPat, TypecheckedMatch )
18 import DsHsSyn ( outPatType )
19 import Check ( check, ExhaustivePat )
22 import DsGRHSs ( dsGRHSs )
24 import Id ( idType, recordSelectorFieldLabel, Id )
25 import DataCon ( dataConFieldLabels, dataConArgTys )
26 import MatchCon ( matchConFamily )
27 import MatchLit ( matchLiterals )
28 import PrelInfo ( pAT_ERROR_ID )
29 import Type ( isUnLiftedType, splitAlgTyConApp,
32 import TysPrim ( intPrimTy, charPrimTy, floatPrimTy, doublePrimTy,
33 addrPrimTy, wordPrimTy
35 import TysWiredIn ( nilDataCon, consDataCon, mkTupleTy, mkListTy,
36 charTy, charDataCon, intTy, intDataCon,
37 floatTy, floatDataCon, doubleTy, tupleCon,
38 doubleDataCon, addrTy,
39 addrDataCon, wordTy, wordDataCon,
40 mkUnboxedTupleTy, unboxedTupleCon
43 import ErrUtils ( addErrLocHdrLine, dontAddErrLoc )
47 This function is a wrapper of @match@, it must be called from all the parts where
48 it was called match, but only substitutes the firs call, ....
49 if the associated flags are declared, warnings will be issued.
50 It can not be called matchWrapper because this name already exists :-(
55 matchExport :: [Id] -- Vars rep'ing the exprs we're matching with
56 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
57 -> DsM MatchResult -- Desugared result!
59 matchExport vars qs@((EqnInfo _ ctx _ (MatchResult _ _)) : _)
60 | incomplete && shadow =
61 dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
62 dsIncompleteWarn ctx pats `thenDs` \ () ->
65 dsIncompleteWarn ctx pats `thenDs` \ () ->
68 dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
72 where (pats,indexs) = check qs
73 incomplete = opt_WarnIncompletePatterns && (length pats /= 0)
74 shadow = opt_WarnOverlappingPatterns && sizeUniqSet indexs < no_eqns
76 unused_eqns = uniqSetToList (mkUniqSet [1..no_eqns] `minusUniqSet` indexs)
77 eqns_shadow = map (\n -> qs!!(n - 1)) unused_eqns
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 _ _) qs = dsWarn warn
95 warn | length qs > maximum_output
96 = pp_context ctx (ptext SLIT("are overlapped"))
97 (\ f -> vcat (map (ppr_eqn f kind) (take maximum_output qs)) $$
100 = pp_context ctx (ptext SLIT("are overlapped"))
101 (\ f -> vcat $ map (ppr_eqn f kind) qs)
104 dsIncompleteWarn :: DsMatchContext -> [ExhaustivePat] -> DsM ()
105 dsIncompleteWarn ctx@(DsMatchContext kind _ _) pats = dsWarn warn
107 warn = pp_context ctx (ptext SLIT("are non-exhaustive"))
108 (\f -> hang (ptext SLIT("Patterns not matched:"))
109 4 ((vcat $ map (ppr_incomplete_pats kind)
110 (take maximum_output pats))
113 dots | length pats > maximum_output = ptext SLIT("...")
116 pp_context NoMatchContext msg rest_of_msg_fun
117 = dontAddErrLoc "" (ptext SLIT("Some match(es)") <+> hang msg 8 (rest_of_msg_fun id))
119 pp_context (DsMatchContext kind pats loc) msg rest_of_msg_fun
120 = case pp_match kind pats of
122 addErrLocHdrLine loc message (nest 8 (rest_of_msg_fun pref))
124 message = ptext SLIT("Pattern match(es)") <+> msg <+> ppr_match <> char ':'
126 pp_match (FunMatch fun) pats
127 = let ppr_fun = ppr fun in
128 ( hsep [ptext SLIT("in the definition of function"), quotes ppr_fun]
129 , (\ x -> ppr_fun <+> x)
132 pp_match CaseMatch pats
133 = (hang (ptext SLIT("in a group of case alternatives beginning"))
138 pp_match RecUpdMatch pats
139 = (hang (ptext SLIT("in a record-update construct"))
144 pp_match PatBindMatch pats
145 = ( hang (ptext SLIT("in a pattern binding"))
150 pp_match LambdaMatch pats
151 = ( hang (ptext SLIT("in a lambda abstraction"))
156 pp_match DoBindMatch pats
157 = ( hang (ptext SLIT("in a `do' pattern binding"))
162 pp_match ListCompMatch pats
163 = ( hang (ptext SLIT("in a `list comprension' pattern binding"))
168 pp_match LetMatch pats
169 = ( hang (ptext SLIT("in a `let' pattern binding"))
174 ppr_pats pats = sep (map ppr pats)
176 separator (FunMatch _) = SLIT("=")
177 separator (CaseMatch) = SLIT("->")
178 separator (LambdaMatch) = SLIT("->")
179 separator (PatBindMatch) = panic "When is this used?"
180 separator (RecUpdMatch) = panic "When is this used?"
181 separator (DoBindMatch) = SLIT("<-")
182 separator (ListCompMatch) = SLIT("<-")
183 separator (LetMatch) = SLIT("=")
185 ppr_shadow_pats kind pats
186 = sep [ppr_pats pats, ptext (separator kind), ptext SLIT("...")]
188 ppr_incomplete_pats kind (pats,[]) = ppr_pats pats
189 ppr_incomplete_pats kind (pats,constraints) =
190 sep [ppr_pats pats, ptext SLIT("with"),
191 sep (map ppr_constraint constraints)]
194 ppr_constraint (var,pats) = sep [ppr var, ptext SLIT("`notElem`"), ppr pats]
196 ppr_eqn prefixF kind (EqnInfo _ _ pats _) = prefixF (ppr_shadow_pats kind pats)
200 The function @match@ is basically the same as in the Wadler chapter,
201 except it is monadised, to carry around the name supply, info about
204 Notes on @match@'s arguments, assuming $m$ equations and $n$ patterns:
207 A list of $n$ variable names, those variables presumably bound to the
208 $n$ expressions being matched against the $n$ patterns. Using the
209 list of $n$ expressions as the first argument showed no benefit and
213 The second argument, a list giving the ``equation info'' for each of
217 the $n$ patterns for that equation, and
219 a list of Core bindings [@(Id, CoreExpr)@ pairs] to be ``stuck on
220 the front'' of the matching code, as in:
226 and finally: (ToDo: fill in)
228 The right way to think about the ``after-match function'' is that it
229 is an embryonic @CoreExpr@ with a ``hole'' at the end for the
230 final ``else expression''.
233 There is a type synonym, @EquationInfo@, defined in module @DsUtils@.
235 An experiment with re-ordering this information about equations (in
236 particular, having the patterns available in column-major order)
240 A default expression---what to evaluate if the overall pattern-match
241 fails. This expression will (almost?) always be
242 a measly expression @Var@, unless we know it will only be used once
243 (as we do in @glue_success_exprs@).
245 Leaving out this third argument to @match@ (and slamming in lots of
246 @Var "fail"@s) is a positively {\em bad} idea, because it makes it
247 impossible to share the default expressions. (Also, it stands no
248 chance of working in our post-upheaval world of @Locals@.)
250 So, the full type signature:
252 match :: [Id] -- Variables rep'ing the exprs we're matching with
253 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
254 -> DsM MatchResult -- Desugared result!
257 Note: @match@ is often called via @matchWrapper@ (end of this module),
258 a function that does much of the house-keeping that goes with a call
261 It is also worth mentioning the {\em typical} way a block of equations
262 is desugared with @match@. At each stage, it is the first column of
263 patterns that is examined. The steps carried out are roughly:
266 Tidy the patterns in column~1 with @tidyEqnInfo@ (this may add
267 bindings to the second component of the equation-info):
270 Remove the `as' patterns from column~1.
272 Make all constructor patterns in column~1 into @ConPats@, notably
273 @ListPats@ and @TuplePats@.
275 Handle any irrefutable (or ``twiddle'') @LazyPats@.
278 Now {\em unmix} the equations into {\em blocks} [w/ local function
279 @unmix_eqns@], in which the equations in a block all have variable
280 patterns in column~1, or they all have constructor patterns in ...
281 (see ``the mixture rule'' in SLPJ).
283 Call @matchUnmixedEqns@ on each block of equations; it will do the
284 appropriate thing for each kind of column-1 pattern, usually ending up
285 in a recursive call to @match@.
288 %************************************************************************
290 %* match: empty rule *
292 %************************************************************************
293 \subsection[Match-empty-rule]{The ``empty rule''}
295 We are a little more paranoid about the ``empty rule'' (SLPJ, p.~87)
296 than the Wadler-chapter code for @match@ (p.~93, first @match@ clause).
297 And gluing the ``success expressions'' together isn't quite so pretty.
301 = complete_matches eqns_info
303 complete_matches [eqn]
306 complete_matches (eqn:eqns)
307 = complete_match eqn `thenDs` \ match_result1 ->
308 complete_matches eqns `thenDs` \ match_result2 ->
309 returnDs (combineMatchResults match_result1 match_result2)
311 complete_match (EqnInfo _ _ pats match_result)
312 = ASSERT( null pats )
313 returnDs match_result
316 %************************************************************************
318 %* match: non-empty rule *
320 %************************************************************************
321 \subsection[Match-nonempty]{@match@ when non-empty: unmixing}
323 This (more interesting) clause of @match@ uses @tidy_and_unmix_eqns@
324 (a)~to get `as'- and `twiddle'-patterns out of the way (tidying), and
325 (b)~to do ``the mixture rule'' (SLPJ, p.~88) [which really {\em
326 un}mixes the equations], producing a list of equation-info
327 blocks, each block having as its first column of patterns either all
328 constructors, or all variables (or similar beasts), etc.
330 @match_unmixed_eqn_blks@ simply takes the place of the @foldr@ in the
331 Wadler-chapter @match@ (p.~93, last clause), and @match_unmixed_blk@
332 corresponds roughly to @matchVarCon@.
335 match vars@(v:vs) eqns_info
336 = mapDs (tidyEqnInfo v) eqns_info `thenDs` \ tidy_eqns_info ->
338 tidy_eqns_blks = unmix_eqns tidy_eqns_info
340 match_unmixed_eqn_blks vars tidy_eqns_blks
343 unmix_eqns [eqn] = [ [eqn] ]
344 unmix_eqns (eq1@(EqnInfo _ _ (p1:p1s) _) : eq2@(EqnInfo _ _ (p2:p2s) _) : eqs)
345 = if ( (isWildPat p1 && isWildPat p2)
346 || (isConPat p1 && isConPat p2)
347 || (isLitPat p1 && isLitPat p2) ) then
348 eq1 `tack_onto` unmixed_rest
350 [ eq1 ] : unmixed_rest
352 unmixed_rest = unmix_eqns (eq2:eqs)
354 x `tack_onto` xss = ( x : head xss) : tail xss
356 -----------------------------------------------------------------------
357 -- loop through the blocks:
358 -- subsequent blocks create a "fail expr" for the first one...
359 match_unmixed_eqn_blks :: [Id]
360 -> [ [EquationInfo] ] -- List of eqn BLOCKS
363 match_unmixed_eqn_blks vars [] = panic "match_unmixed_eqn_blks"
365 match_unmixed_eqn_blks vars [eqn_blk] = matchUnmixedEqns vars eqn_blk
367 match_unmixed_eqn_blks vars (eqn_blk:eqn_blks)
368 = matchUnmixedEqns vars eqn_blk `thenDs` \ match_result1 -> -- try to match with first blk
369 match_unmixed_eqn_blks vars eqn_blks `thenDs` \ match_result2 ->
370 returnDs (combineMatchResults match_result1 match_result2)
373 Tidy up the leftmost pattern in an @EquationInfo@, given the variable @v@
374 which will be scrutinised. This means:
377 Replace variable patterns @x@ (@x /= v@) with the pattern @_@,
378 together with the binding @x = v@.
380 Replace the `as' pattern @x@@p@ with the pattern p and a binding @x = v@.
382 Removing lazy (irrefutable) patterns (you don't want to know...).
384 Converting explicit tuple- and list-pats into ordinary @ConPats@.
386 Convert the literal pat "" to [].
389 The result of this tidying is that the column of patterns will include
393 The @VarPat@ information isn't needed any more after this.
396 @ListPats@, @TuplePats@, etc., are all converted into @ConPats@.
398 \item[@LitPats@ and @NPats@:]
399 @LitPats@/@NPats@ of ``known friendly types'' (Int, Char,
400 Float, Double, at least) are converted to unboxed form; e.g.,
401 \tr{(NPat (HsInt i) _ _)} is converted to:
403 (ConPat I# _ _ [LitPat (HsIntPrim i) _])
408 tidyEqnInfo :: Id -> EquationInfo -> DsM EquationInfo
409 -- DsM'd because of internal call to "match".
410 -- "tidy1" does the interesting stuff, looking at
411 -- one pattern and fiddling the list of bindings.
413 -- POST CONDITION: head pattern in the EqnInfo is
421 tidyEqnInfo v (EqnInfo n ctx (pat : pats) match_result)
422 = tidy1 v pat match_result `thenDs` \ (pat', match_result') ->
423 returnDs (EqnInfo n ctx (pat' : pats) match_result')
425 tidy1 :: Id -- The Id being scrutinised
426 -> TypecheckedPat -- The pattern against which it is to be matched
427 -> MatchResult -- Current thing do do after matching
428 -> DsM (TypecheckedPat, -- Equivalent pattern
429 MatchResult) -- Augmented thing to do afterwards
430 -- The augmentation usually takes the form
431 -- of new bindings to be added to the front
433 tidy1 v (VarPat var) match_result
434 = returnDs (WildPat (idType var), match_result')
436 match_result' | v == var = match_result
437 | otherwise = adjustMatchResult (bindNonRec var (Var v)) match_result
439 tidy1 v (AsPat var pat) match_result
440 = tidy1 v pat match_result'
442 match_result' | v == var = match_result
443 | otherwise = adjustMatchResult (bindNonRec var (Var v)) match_result
445 tidy1 v (WildPat ty) match_result
446 = returnDs (WildPat ty, match_result)
448 {- now, here we handle lazy patterns:
449 tidy1 v ~p bs = (v, v1 = case v of p -> v1 :
450 v2 = case v of p -> v2 : ... : bs )
452 where the v_i's are the binders in the pattern.
454 ToDo: in "v_i = ... -> v_i", are the v_i's really the same thing?
456 The case expr for v_i is just: match [v] [(p, [], \ x -> Var v_i)] any_expr
459 tidy1 v (LazyPat pat) match_result
460 = mkSelectorBinds pat (Var v) `thenDs` \ sel_binds ->
461 returnDs (WildPat (idType v),
462 mkCoLetsMatchResult [NonRec b rhs | (b,rhs) <- sel_binds] match_result)
464 -- re-express <con-something> as (ConPat ...) [directly]
466 tidy1 v (RecPat data_con pat_ty ex_tvs dicts rpats) match_result
468 = -- Special case for C {}, which can be used for
469 -- a constructor that isn't declared to have
471 returnDs (ConPat data_con pat_ty ex_tvs dicts (map WildPat con_arg_tys'), match_result)
474 = returnDs (ConPat data_con pat_ty ex_tvs dicts pats, match_result)
476 pats = map mk_pat tagged_arg_tys
478 -- Boring stuff to find the arg-tys of the constructor
479 (_, inst_tys, _) = splitAlgTyConApp pat_ty
480 con_arg_tys' = dataConArgTys data_con (inst_tys ++ mkTyVarTys ex_tvs)
481 tagged_arg_tys = con_arg_tys' `zip` (dataConFieldLabels data_con)
483 -- mk_pat picks a WildPat of the appropriate type for absent fields,
484 -- and the specified pattern for present fields
485 mk_pat (arg_ty, lbl) = case [pat | (sel_id,pat,_) <- rpats,
486 recordSelectorFieldLabel sel_id == lbl
488 (pat:pats) -> ASSERT( null pats )
492 tidy1 v (ListPat ty pats) match_result
493 = returnDs (list_ConPat, match_result)
495 list_ty = mkListTy ty
497 = foldr (\ x -> \y -> ConPat consDataCon list_ty [] [] [x, y])
498 (ConPat nilDataCon list_ty [] [] [])
501 tidy1 v (TuplePat pats True{-boxed-}) match_result
502 = returnDs (tuple_ConPat, match_result)
506 = ConPat (tupleCon arity)
507 (mkTupleTy arity (map outPatType pats)) [] []
510 tidy1 v (TuplePat pats False{-unboxed-}) match_result
511 = returnDs (tuple_ConPat, match_result)
515 = ConPat (unboxedTupleCon arity)
516 (mkUnboxedTupleTy arity (map outPatType pats)) [] []
519 tidy1 v (DictPat dicts methods) match_result
520 = case num_of_d_and_ms of
521 0 -> tidy1 v (TuplePat [] True) match_result
522 1 -> tidy1 v (head dict_and_method_pats) match_result
523 _ -> tidy1 v (TuplePat dict_and_method_pats True) match_result
525 num_of_d_and_ms = length dicts + length methods
526 dict_and_method_pats = map VarPat (dicts ++ methods)
529 -- deeply ugly mangling for some (common) NPats/LitPats
531 -- LitPats: the desugarer only sees these at well-known types
533 tidy1 v pat@(LitPat lit lit_ty) match_result
534 = returnDs (tidyLitPat lit lit_ty pat, match_result)
536 -- NPats: we *might* be able to replace these w/ a simpler form
537 tidy1 v pat@(NPat lit lit_ty _) match_result
538 = returnDs (tidyLitPat lit lit_ty pat, match_result)
540 -- and everything else goes through unchanged...
542 tidy1 v non_interesting_pat match_result
543 = returnDs (non_interesting_pat, match_result)
547 {\bf Previous @matchTwiddled@ stuff:}
549 Now we get to the only interesting part; note: there are choices for
550 translation [from Simon's notes]; translation~1:
557 s = case w of [s,t] -> s
558 t = case w of [s,t] -> t
562 Here \tr{w} is a fresh variable, and the \tr{w}-binding prevents multiple
563 evaluation of \tr{e}. An alternative translation (No.~2):
565 [ w = case e of [s,t] -> (s,t)
566 s = case w of (s,t) -> s
567 t = case w of (s,t) -> t
571 %************************************************************************
573 \subsubsection[improved-unmixing]{UNIMPLEMENTED idea for improved unmixing}
575 %************************************************************************
577 We might be able to optimise unmixing when confronted by
578 only-one-constructor-possible, of which tuples are the most notable
586 This definition would normally be unmixed into four equation blocks,
587 one per equation. But it could be unmixed into just one equation
588 block, because if the one equation matches (on the first column),
589 the others certainly will.
591 You have to be careful, though; the example
599 {\em must} be broken into two blocks at the line shown; otherwise, you
600 are forcing unnecessary evaluation. In any case, the top-left pattern
601 always gives the cue. You could then unmix blocks into groups of...
603 \item[all variables:]
605 \item[constructors or variables (mixed):]
606 Need to make sure the right names get bound for the variable patterns.
607 \item[literals or variables (mixed):]
608 Presumably just a variant on the constructor case (as it is now).
611 %************************************************************************
613 %* match on an unmixed block: the real business *
615 %************************************************************************
616 \subsection[matchUnmixedEqns]{@matchUnmixedEqns@: getting down to business}
618 The function @matchUnmixedEqns@ is where the matching stuff sets to
619 work a block of equations, to which the mixture rule has been applied.
620 Its arguments and results are the same as for the ``top-level'' @match@.
623 matchUnmixedEqns :: [Id]
627 matchUnmixedEqns [] _ = panic "matchUnmixedEqns: no names"
629 matchUnmixedEqns all_vars@(var:vars) eqns_info
630 | isWildPat first_pat
631 = ASSERT( all isWildPat column_1_pats ) -- Sanity check
632 -- Real true variables, just like in matchVar, SLPJ p 94
633 -- No binding to do: they'll all be wildcards by now (done in tidy)
634 match vars remaining_eqns_info
637 = ASSERT( patsAreAllCons column_1_pats )
638 matchConFamily all_vars eqns_info
641 = ASSERT( patsAreAllLits column_1_pats )
642 -- see notes in MatchLiteral
643 -- not worried about the same literal more than once in a column
644 -- (ToDo: sort this out later)
645 matchLiterals all_vars eqns_info
648 first_pat = head column_1_pats
649 column_1_pats = [pat | EqnInfo _ _ (pat:_) _ <- eqns_info]
650 remaining_eqns_info = [EqnInfo n ctx pats match_result | EqnInfo n ctx (_:pats) match_result <- eqns_info]
653 %************************************************************************
655 %* matchWrapper: a convenient way to call @match@ *
657 %************************************************************************
658 \subsection[matchWrapper]{@matchWrapper@: a convenient interface to @match@}
660 Calls to @match@ often involve similar (non-trivial) work; that work
661 is collected here, in @matchWrapper@. This function takes as
665 Typchecked @Matches@ (of a function definition, or a case or lambda
666 expression)---the main input;
668 An error message to be inserted into any (runtime) pattern-matching
672 As results, @matchWrapper@ produces:
675 A list of variables (@Locals@) that the caller must ``promise'' to
676 bind to appropriate values; and
678 a @CoreExpr@, the desugared output (main result).
681 The main actions of @matchWrapper@ include:
684 Flatten the @[TypecheckedMatch]@ into a suitable list of
687 Create as many new variables as there are patterns in a pattern-list
688 (in any one of the @EquationInfo@s).
690 Create a suitable ``if it fails'' expression---a call to @error@ using
691 the error-string input; the {\em type} of this fail value can be found
692 by examining one of the RHS expressions in one of the @EquationInfo@s.
694 Call @match@ with all of this information!
698 matchWrapper :: DsMatchKind -- For shadowing warning messages
699 -> [TypecheckedMatch] -- Matches being desugared
700 -> String -- Error message if the match fails
701 -> DsM ([Id], CoreExpr) -- Results
704 There is one small problem with the Lambda Patterns, when somebody
705 writes something similar to:
709 he/she don't want a warning about incomplete patterns, that is done with
710 the flag @opt_WarnSimplePatterns@.
711 This problem also appears in the:
713 \item @do@ patterns, but if the @do@ can fail
714 it creates another equation if the match can fail
715 (see @DsExpr.doDo@ function)
716 \item @let@ patterns, are treated by @matchSimply@
717 List Comprension Patterns, are treated by @matchSimply@ also
720 We can't call @matchSimply@ with Lambda patterns,
721 due to the fact that lambda patterns can have more than
722 one pattern, and match simply only accepts one pattern.
727 matchWrapper kind matches error_string
728 = flattenMatches kind matches `thenDs` \ (result_ty, eqns_info) ->
730 EqnInfo _ _ arg_pats _ : _ = eqns_info
732 mapDs selectMatchVar arg_pats `thenDs` \ new_vars ->
733 match_fun new_vars eqns_info `thenDs` \ match_result ->
735 mkErrorAppDs pAT_ERROR_ID result_ty error_string `thenDs` \ fail_expr ->
736 extractMatchResult match_result fail_expr `thenDs` \ result_expr ->
737 returnDs (new_vars, result_expr)
738 where match_fun = case kind of
739 LambdaMatch | opt_WarnSimplePatterns -> matchExport
744 %************************************************************************
746 \subsection[matchSimply]{@matchSimply@: match a single expression against a single pattern}
748 %************************************************************************
750 @mkSimpleMatch@ is a wrapper for @match@ which deals with the
751 situation where we want to match a single expression against a single
752 pattern. It returns an expression.
755 matchSimply :: CoreExpr -- Scrutinee
756 -> DsMatchKind -- Match kind
757 -> TypecheckedPat -- Pattern it should match
758 -> CoreExpr -- Return this if it matches
759 -> CoreExpr -- Return this if it doesn't
762 matchSimply scrut kind pat result_expr fail_expr
763 = getSrcLocDs `thenDs` \ locn ->
765 ctx = DsMatchContext kind [pat] locn
766 match_result = cantFailMatchResult result_expr
768 matchSinglePat scrut ctx pat match_result `thenDs` \ match_result' ->
769 extractMatchResult match_result' fail_expr
772 matchSinglePat :: CoreExpr -> DsMatchContext -> TypecheckedPat
773 -> MatchResult -> DsM MatchResult
775 matchSinglePat (Var var) ctx pat match_result
776 = match_fn [var] [EqnInfo 1 ctx [pat] match_result]
778 match_fn | opt_WarnSimplePatterns = matchExport
781 matchSinglePat scrut ctx pat match_result
782 = selectMatchVar pat `thenDs` \ var ->
783 matchSinglePat (Var var) ctx pat match_result `thenDs` \ match_result' ->
784 returnDs (adjustMatchResult (bindNonRec var scrut) match_result')
787 %************************************************************************
789 %* flattenMatches : create a list of EquationInfo *
791 %************************************************************************
793 \subsection[flattenMatches]{@flattenMatches@: create @[EquationInfo]@}
795 This is actually local to @matchWrapper@.
800 -> [TypecheckedMatch]
801 -> DsM (Type, [EquationInfo])
803 flattenMatches kind matches
804 = mapAndUnzipDs flatten_match (matches `zip` [1..]) `thenDs` \ (result_tys, eqn_infos) ->
806 result_ty = head result_tys
808 ASSERT( all (== result_ty) result_tys )
809 returnDs (result_ty, eqn_infos)
811 flatten_match (Match _ pats _ grhss, n)
812 = dsGRHSs kind pats grhss `thenDs` \ (ty, match_result) ->
813 getSrcLocDs `thenDs` \ locn ->
814 returnDs (ty, EqnInfo n (DsMatchContext kind pats locn) pats match_result)