2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[Main_match]{The @match@ function}
7 #include "HsVersions.h"
9 module Match ( match, matchWrapper, matchSimply ) where
12 IMPORT_DELOOPER(DsLoop) -- here for paranoia-checking reasons
13 -- and to break dsExpr/dsBinds-ish loop
15 import CmdLineOpts ( opt_WarnIncompletePatterns )
17 import TcHsSyn ( SYN_IE(TypecheckedPat), SYN_IE(TypecheckedMatch),
18 SYN_IE(TypecheckedHsBinds), SYN_IE(TypecheckedHsExpr) )
19 import DsHsSyn ( outPatType, collectTypedPatBinders )
22 import CoreUtils ( coreExprType )
24 import DsGRHSs ( dsGRHSs )
26 import MatchCon ( matchConFamily )
27 import MatchLit ( matchLiterals )
29 import FieldLabel ( FieldLabel {- Eq instance -} )
30 import Id ( idType, dataConFieldLabels,
31 dataConArgTys, recordSelectorFieldLabel,
32 GenId{-instance-}, SYN_IE(Id)
34 import Name ( Name {--O only-} )
35 import PprStyle ( PprStyle(..) )
36 import PprType ( GenType{-instance-}, GenTyVar{-ditto-} )
38 import PrelVals ( pAT_ERROR_ID )
39 import Type ( isPrimType, eqTy, getAppDataTyConExpandingDicts,
40 instantiateTauTy, SYN_IE(Type)
42 import TyVar ( GenTyVar{-instance Eq-}, SYN_IE(TyVar) )
43 import TysPrim ( intPrimTy, charPrimTy, floatPrimTy, doublePrimTy,
44 addrPrimTy, wordPrimTy
46 import TysWiredIn ( nilDataCon, consDataCon, mkTupleTy, mkListTy,
47 charTy, charDataCon, intTy, intDataCon,
48 floatTy, floatDataCon, doubleTy, tupleCon,
49 doubleDataCon, stringTy, addrTy,
50 addrDataCon, wordTy, wordDataCon
52 import Unique ( Unique{-instance Eq-} )
53 import Util ( panic, pprPanic, assertPanic )
54 #if __GLASGOW_HASKELL__ >= 202
55 import Outputable ( Outputable(..) )
60 The function @match@ is basically the same as in the Wadler chapter,
61 except it is monadised, to carry around the name supply, info about
64 Notes on @match@'s arguments, assuming $m$ equations and $n$ patterns:
67 A list of $n$ variable names, those variables presumably bound to the
68 $n$ expressions being matched against the $n$ patterns. Using the
69 list of $n$ expressions as the first argument showed no benefit and
73 The second argument, a list giving the ``equation info'' for each of
77 the $n$ patterns for that equation, and
79 a list of Core bindings [@(Id, CoreExpr)@ pairs] to be ``stuck on
80 the front'' of the matching code, as in:
86 and finally: (ToDo: fill in)
88 The right way to think about the ``after-match function'' is that it
89 is an embryonic @CoreExpr@ with a ``hole'' at the end for the
90 final ``else expression''.
93 There is a type synonym, @EquationInfo@, defined in module @DsUtils@.
95 An experiment with re-ordering this information about equations (in
96 particular, having the patterns available in column-major order)
100 A default expression---what to evaluate if the overall pattern-match
101 fails. This expression will (almost?) always be
102 a measly expression @Var@, unless we know it will only be used once
103 (as we do in @glue_success_exprs@).
105 Leaving out this third argument to @match@ (and slamming in lots of
106 @Var "fail"@s) is a positively {\em bad} idea, because it makes it
107 impossible to share the default expressions. (Also, it stands no
108 chance of working in our post-upheaval world of @Locals@.)
110 So, the full type signature:
112 match :: [Id] -- Variables rep'ing the exprs we're matching with
113 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
114 -> [EquationInfo] -- Potentially shadowing equations above this one
115 -> DsM MatchResult -- Desugared result!
118 Note: @match@ is often called via @matchWrapper@ (end of this module),
119 a function that does much of the house-keeping that goes with a call
122 It is also worth mentioning the {\em typical} way a block of equations
123 is desugared with @match@. At each stage, it is the first column of
124 patterns that is examined. The steps carried out are roughly:
127 Tidy the patterns in column~1 with @tidyEqnInfo@ (this may add
128 bindings to the second component of the equation-info):
131 Remove the `as' patterns from column~1.
133 Make all constructor patterns in column~1 into @ConPats@, notably
134 @ListPats@ and @TuplePats@.
136 Handle any irrefutable (or ``twiddle'') @LazyPats@.
139 Now {\em unmix} the equations into {\em blocks} [w/ local function
140 @unmix_eqns@], in which the equations in a block all have variable
141 patterns in column~1, or they all have constructor patterns in ...
142 (see ``the mixture rule'' in SLPJ).
144 Call @matchUnmixedEqns@ on each block of equations; it will do the
145 appropriate thing for each kind of column-1 pattern, usually ending up
146 in a recursive call to @match@.
149 %************************************************************************
151 %* match: empty rule *
153 %************************************************************************
154 \subsection[Match-empty-rule]{The ``empty rule''}
156 We are a little more paranoid about the ``empty rule'' (SLPJ, p.~87)
157 than the Wadler-chapter code for @match@ (p.~93, first @match@ clause).
158 And gluing the ``success expressions'' together isn't quite so pretty.
161 match [] eqns_info shadows
162 = complete_matches eqns_info (any eqn_cant_fail shadows)
164 complete_matches [eqn] is_shadowed
165 = complete_match eqn is_shadowed
167 complete_matches (eqn:eqns) is_shadowed
168 = complete_match eqn is_shadowed `thenDs` \ match_result1 ->
169 complete_matches eqns (is_shadowed || eqn_cant_fail eqn) `thenDs` \ match_result2 ->
170 combineMatchResults match_result1 match_result2
172 -- If at this stage we find that at least one of the shadowing
173 -- equations is guaranteed not to fail, then warn of an overlapping pattern
174 complete_match (EqnInfo [] match_result@(MatchResult _ _ _ cxt)) is_shadowed
175 | is_shadowed = dsShadowWarn cxt `thenDs` \ _ ->
176 returnDs match_result
178 | otherwise = returnDs match_result
180 eqn_cant_fail :: EquationInfo -> Bool
181 eqn_cant_fail (EqnInfo [] (MatchResult CanFail _ _ _)) = False
182 eqn_cant_fail (EqnInfo [] (MatchResult CantFail _ _ _)) = True
185 %************************************************************************
187 %* match: non-empty rule *
189 %************************************************************************
190 \subsection[Match-nonempty]{@match@ when non-empty: unmixing}
192 This (more interesting) clause of @match@ uses @tidy_and_unmix_eqns@
193 (a)~to get `as'- and `twiddle'-patterns out of the way (tidying), and
194 (b)~to do ``the mixture rule'' (SLPJ, p.~88) [which really {\em
195 un}mixes the equations], producing a list of equation-info
196 blocks, each block having as its first column of patterns either all
197 constructors, or all variables (or similar beasts), etc.
199 @match_unmixed_eqn_blks@ simply takes the place of the @foldr@ in the
200 Wadler-chapter @match@ (p.~93, last clause), and @match_unmixed_blk@
201 corresponds roughly to @matchVarCon@.
204 match vars@(v:vs) eqns_info shadows
205 = mapDs (tidyEqnInfo v) eqns_info `thenDs` \ tidy_eqns_info ->
206 mapDs (tidyEqnInfo v) shadows `thenDs` \ tidy_shadows ->
208 tidy_eqns_blks = unmix_eqns tidy_eqns_info
210 match_unmixed_eqn_blks vars tidy_eqns_blks tidy_shadows
213 unmix_eqns [eqn] = [ [eqn] ]
214 unmix_eqns (eq1@(EqnInfo (p1:p1s) _) : eq2@(EqnInfo (p2:p2s) _) : eqs)
215 = if ( (irrefutablePat p1 && irrefutablePat p2)
216 || (isConPat p1 && isConPat p2)
217 || (isLitPat p1 && isLitPat p2) ) then
218 eq1 `tack_onto` unmixed_rest
220 [ eq1 ] : unmixed_rest
222 unmixed_rest = unmix_eqns (eq2:eqs)
224 x `tack_onto` xss = ( x : head xss) : tail xss
226 -----------------------------------------------------------------------
227 -- loop through the blocks:
228 -- subsequent blocks create a "fail expr" for the first one...
229 match_unmixed_eqn_blks :: [Id]
230 -> [ [EquationInfo] ] -- List of eqn BLOCKS
231 -> [EquationInfo] -- Shadows
234 match_unmixed_eqn_blks vars [] shadows = panic "match_unmixed_eqn_blks"
236 match_unmixed_eqn_blks vars [eqn_blk] shadows = matchUnmixedEqns vars eqn_blk shadows
238 match_unmixed_eqn_blks vars (eqn_blk:eqn_blks) shadows
239 = matchUnmixedEqns vars eqn_blk shadows `thenDs` \ match_result1 -> -- try to match with first blk
240 match_unmixed_eqn_blks vars eqn_blks shadows' `thenDs` \ match_result2 ->
241 combineMatchResults match_result1 match_result2
243 shadows' = eqn_blk ++ shadows
246 Tidy up the leftmost pattern in an @EquationInfo@, given the variable @v@
247 which will be scrutinised. This means:
250 Replace variable patterns @x@ (@x /= v@) with the pattern @_@,
251 together with the binding @x = v@.
253 Replace the `as' pattern @x@@p@ with the pattern p and a binding @x = v@.
255 Removing lazy (irrefutable) patterns (you don't want to know...).
257 Converting explicit tuple- and list-pats into ordinary @ConPats@.
259 Convert the literal pat "" to [].
262 The result of this tidying is that the column of patterns will include
266 The @VarPat@ information isn't needed any more after this.
269 @ListPats@, @TuplePats@, etc., are all converted into @ConPats@.
271 \item[@LitPats@ and @NPats@:]
272 @LitPats@/@NPats@ of ``known friendly types'' (Int, Char,
273 Float, Double, at least) are converted to unboxed form; e.g.,
274 \tr{(NPat (HsInt i) _ _)} is converted to:
276 (ConPat I# _ _ [LitPat (HsIntPrim i) _])
281 tidyEqnInfo :: Id -> EquationInfo -> DsM EquationInfo
282 -- DsM'd because of internal call to "match".
283 -- "tidy1" does the interesting stuff, looking at
284 -- one pattern and fiddling the list of bindings.
285 tidyEqnInfo v (EqnInfo (pat : pats) match_result)
286 = tidy1 v pat match_result `thenDs` \ (pat', match_result') ->
287 returnDs (EqnInfo (pat' : pats) match_result')
289 tidy1 :: Id -- The Id being scrutinised
290 -> TypecheckedPat -- The pattern against which it is to be matched
291 -> MatchResult -- Current thing do do after matching
292 -> DsM (TypecheckedPat, -- Equivalent pattern
293 MatchResult) -- Augmented thing to do afterwards
294 -- The augmentation usually takes the form
295 -- of new bindings to be added to the front
297 tidy1 v (VarPat var) match_result
298 = returnDs (WildPat (idType var),
299 mkCoLetsMatchResult extra_binds match_result)
301 extra_binds | v == var = []
302 | otherwise = [NonRec var (Var v)]
304 tidy1 v (AsPat var pat) match_result
305 = tidy1 v pat (mkCoLetsMatchResult extra_binds match_result)
307 extra_binds | v == var = []
308 | otherwise = [NonRec var (Var v)]
310 tidy1 v (WildPat ty) match_result
311 = returnDs (WildPat ty, match_result)
313 {- now, here we handle lazy patterns:
314 tidy1 v ~p bs = (v, v1 = case v of p -> v1 :
315 v2 = case v of p -> v2 : ... : bs )
317 where the v_i's are the binders in the pattern.
319 ToDo: in "v_i = ... -> v_i", are the v_i's really the same thing?
321 The case expr for v_i is just: match [v] [(p, [], \ x -> Var v_i)] any_expr
324 tidy1 v (LazyPat pat) match_result
325 = mkSelectorBinds pat (Var v) `thenDs` \ sel_binds ->
326 returnDs (WildPat (idType v),
327 mkCoLetsMatchResult [NonRec b rhs | (b,rhs) <- sel_binds] match_result)
329 -- re-express <con-something> as (ConPat ...) [directly]
331 tidy1 v (ConOpPat pat1 id pat2 ty) match_result
332 = returnDs (ConPat id ty [pat1, pat2], match_result)
334 tidy1 v (RecPat con_id pat_ty rpats) match_result
335 = returnDs (ConPat con_id pat_ty pats, match_result)
337 pats = map mk_pat tagged_arg_tys
339 -- Boring stuff to find the arg-tys of the constructor
340 (_, inst_tys, _) = {-trace "Match.getAppDataTyConExpandingDicts" $-} getAppDataTyConExpandingDicts pat_ty
341 con_arg_tys' = dataConArgTys con_id inst_tys
342 tagged_arg_tys = con_arg_tys' `zip` (dataConFieldLabels con_id)
344 -- mk_pat picks a WildPat of the appropriate type for absent fields,
345 -- and the specified pattern for present fields
346 mk_pat (arg_ty, lbl) = case [pat | (sel_id,pat,_) <- rpats,
347 recordSelectorFieldLabel sel_id == lbl
349 (pat:pats) -> ASSERT( null pats )
353 tidy1 v (ListPat ty pats) match_result
354 = returnDs (list_ConPat, match_result)
356 list_ty = mkListTy ty
358 = foldr (\ x -> \y -> ConPat consDataCon list_ty [x, y])
359 (ConPat nilDataCon list_ty [])
362 tidy1 v (TuplePat pats) match_result
363 = returnDs (tuple_ConPat, match_result)
367 = ConPat (tupleCon arity)
368 (mkTupleTy arity (map outPatType pats))
371 tidy1 v (DictPat dicts methods) match_result
372 = case num_of_d_and_ms of
373 0 -> tidy1 v (TuplePat []) match_result
374 1 -> tidy1 v (head dict_and_method_pats) match_result
375 _ -> tidy1 v (TuplePat dict_and_method_pats) match_result
377 num_of_d_and_ms = length dicts + length methods
378 dict_and_method_pats = map VarPat (dicts ++ methods)
381 -- deeply ugly mangling for some (common) NPats/LitPats
383 -- LitPats: the desugarer only sees these at well-known types
385 tidy1 v pat@(LitPat lit lit_ty) match_result
387 = returnDs (pat, match_result)
389 | lit_ty `eqTy` charTy
390 = returnDs (ConPat charDataCon charTy [LitPat (mk_char lit) charPrimTy],
393 | otherwise = pprPanic "tidy1:LitPat:" (ppr PprDebug pat)
395 mk_char (HsChar c) = HsCharPrim c
397 -- NPats: we *might* be able to replace these w/ a simpler form
400 tidy1 v pat@(NPat lit lit_ty _) match_result
401 = returnDs (better_pat, match_result)
404 | lit_ty `eqTy` charTy = ConPat charDataCon lit_ty [LitPat (mk_char lit) charPrimTy]
405 | lit_ty `eqTy` intTy = ConPat intDataCon lit_ty [LitPat (mk_int lit) intPrimTy]
406 | lit_ty `eqTy` wordTy = ConPat wordDataCon lit_ty [LitPat (mk_word lit) wordPrimTy]
407 | lit_ty `eqTy` addrTy = ConPat addrDataCon lit_ty [LitPat (mk_addr lit) addrPrimTy]
408 | lit_ty `eqTy` floatTy = ConPat floatDataCon lit_ty [LitPat (mk_float lit) floatPrimTy]
409 | lit_ty `eqTy` doubleTy = ConPat doubleDataCon lit_ty [LitPat (mk_double lit) doublePrimTy]
411 -- Convert the literal pattern "" to the constructor pattern [].
412 | null_str_lit lit = ConPat nilDataCon lit_ty []
416 mk_int (HsInt i) = HsIntPrim i
417 mk_int l@(HsLitLit s) = l
419 mk_char (HsChar c) = HsCharPrim c
420 mk_char l@(HsLitLit s) = l
422 mk_word l@(HsLitLit s) = l
424 mk_addr l@(HsLitLit s) = l
426 mk_float (HsInt i) = HsFloatPrim (fromInteger i)
427 mk_float (HsFrac f) = HsFloatPrim f
428 mk_float l@(HsLitLit s) = l
430 mk_double (HsInt i) = HsDoublePrim (fromInteger i)
431 mk_double (HsFrac f) = HsDoublePrim f
432 mk_double l@(HsLitLit s) = l
434 null_str_lit (HsString s) = _NULL_ s
435 null_str_lit other_lit = False
437 -- and everything else goes through unchanged...
439 tidy1 v non_interesting_pat match_result
440 = returnDs (non_interesting_pat, match_result)
443 PREVIOUS matchTwiddled STUFF:
445 Now we get to the only interesting part; note: there are choices for
446 translation [from Simon's notes]; translation~1:
453 s = case w of [s,t] -> s
454 t = case w of [s,t] -> t
458 Here \tr{w} is a fresh variable, and the \tr{w}-binding prevents multiple
459 evaluation of \tr{e}. An alternative translation (No.~2):
461 [ w = case e of [s,t] -> (s,t)
462 s = case w of (s,t) -> s
463 t = case w of (s,t) -> t
467 %************************************************************************
469 \subsubsection[improved-unmixing]{UNIMPLEMENTED idea for improved unmixing}
471 %************************************************************************
473 We might be able to optimise unmixing when confronted by
474 only-one-constructor-possible, of which tuples are the most notable
482 This definition would normally be unmixed into four equation blocks,
483 one per equation. But it could be unmixed into just one equation
484 block, because if the one equation matches (on the first column),
485 the others certainly will.
487 You have to be careful, though; the example
495 {\em must} be broken into two blocks at the line shown; otherwise, you
496 are forcing unnecessary evaluation. In any case, the top-left pattern
497 always gives the cue. You could then unmix blocks into groups of...
499 \item[all variables:]
501 \item[constructors or variables (mixed):]
502 Need to make sure the right names get bound for the variable patterns.
503 \item[literals or variables (mixed):]
504 Presumably just a variant on the constructor case (as it is now).
507 %************************************************************************
509 %* match on an unmixed block: the real business *
511 %************************************************************************
512 \subsection[matchUnmixedEqns]{@matchUnmixedEqns@: getting down to business}
514 The function @matchUnmixedEqns@ is where the matching stuff sets to
515 work a block of equations, to which the mixture rule has been applied.
516 Its arguments and results are the same as for the ``top-level'' @match@.
519 matchUnmixedEqns :: [Id]
521 -> [EquationInfo] -- Shadows
524 matchUnmixedEqns [] _ _ = panic "matchUnmixedEqns: no names"
526 matchUnmixedEqns all_vars@(var:vars) eqns_info shadows
527 | irrefutablePat first_pat
528 = ASSERT( irrefutablePats column_1_pats ) -- Sanity check
529 -- Real true variables, just like in matchVar, SLPJ p 94
530 match vars remaining_eqns_info remaining_shadows
533 = ASSERT( patsAreAllCons column_1_pats )
534 matchConFamily all_vars eqns_info shadows
537 = ASSERT( patsAreAllLits column_1_pats )
538 -- see notes in MatchLiteral
539 -- not worried about the same literal more than once in a column
540 -- (ToDo: sort this out later)
541 matchLiterals all_vars eqns_info shadows
544 first_pat = head column_1_pats
545 column_1_pats = [pat | EqnInfo (pat:_) _ <- eqns_info]
546 remaining_eqns_info = [EqnInfo pats match_result | EqnInfo (_:pats) match_result <- eqns_info]
547 remaining_shadows = [EqnInfo pats match_result | EqnInfo (pat:pats) match_result <- shadows,
549 -- Discard shadows which can be refuted, since they don't shadow
553 %************************************************************************
555 %* matchWrapper: a convenient way to call @match@ *
557 %************************************************************************
558 \subsection[matchWrapper]{@matchWrapper@: a convenient interface to @match@}
560 Calls to @match@ often involve similar (non-trivial) work; that work
561 is collected here, in @matchWrapper@. This function takes as
565 Typchecked @Matches@ (of a function definition, or a case or lambda
566 expression)---the main input;
568 An error message to be inserted into any (runtime) pattern-matching
572 As results, @matchWrapper@ produces:
575 A list of variables (@Locals@) that the caller must ``promise'' to
576 bind to appropriate values; and
578 a @CoreExpr@, the desugared output (main result).
581 The main actions of @matchWrapper@ include:
584 Flatten the @[TypecheckedMatch]@ into a suitable list of
587 Create as many new variables as there are patterns in a pattern-list
588 (in any one of the @EquationInfo@s).
590 Create a suitable ``if it fails'' expression---a call to @error@ using
591 the error-string input; the {\em type} of this fail value can be found
592 by examining one of the RHS expressions in one of the @EquationInfo@s.
594 Call @match@ with all of this information!
598 matchWrapper :: DsMatchKind -- For shadowing warning messages
599 -> [TypecheckedMatch] -- Matches being desugared
600 -> String -- Error message if the match fails
601 -> DsM ([Id], CoreExpr) -- Results
603 -- a special case for the common ...:
605 -- lots of (all?) unfailable pats
609 matchWrapper kind [(PatMatch (VarPat var) match)] error_string
610 = matchWrapper kind [match] error_string `thenDs` \ (vars, core_expr) ->
611 returnDs (var:vars, core_expr)
613 matchWrapper kind [(PatMatch (WildPat ty) match)] error_string
614 = newSysLocalDs ty `thenDs` \ var ->
615 matchWrapper kind [match] error_string `thenDs` \ (vars, core_expr) ->
616 returnDs (var:vars, core_expr)
618 matchWrapper kind [(GRHSMatch
619 (GRHSsAndBindsOut [OtherwiseGRHS expr _] binds _))] error_string
620 = dsBinds binds `thenDs` \ core_binds ->
621 dsExpr expr `thenDs` \ core_expr ->
622 returnDs ([], mkCoLetsAny core_binds core_expr)
624 ----------------------------------------------------------------------------
625 -- and all the rest... (general case)
627 matchWrapper kind matches error_string
628 = flattenMatches kind matches `thenDs` \ eqns_info@(EqnInfo arg_pats (MatchResult _ result_ty _ _) : _) ->
630 selectMatchVars arg_pats `thenDs` \ new_vars ->
631 match new_vars eqns_info [] `thenDs` \ match_result ->
633 mkErrorAppDs pAT_ERROR_ID result_ty error_string `thenDs` \ fail_expr ->
635 -- Check for incomplete pattern match
636 (case match_result of
637 MatchResult CanFail result_ty match_fn cxt
638 | opt_WarnIncompletePatterns
639 -> dsIncompleteWarn cxt
643 extractMatchResult match_result fail_expr `thenDs` \ result_expr ->
644 returnDs (new_vars, result_expr)
647 %************************************************************************
649 \subsection[matchSimply]{@matchSimply@: match a single expression against a single pattern}
651 %************************************************************************
653 @mkSimpleMatch@ is a wrapper for @match@ which deals with the
654 situation where we want to match a single expression against a single
655 pattern. It returns an expression.
658 matchSimply :: CoreExpr -- Scrutinee
659 -> TypecheckedPat -- Pattern it should match
660 -> Type -- Type of result
661 -> CoreExpr -- Return this if it matches
662 -> CoreExpr -- Return this if it does
665 matchSimply (Var var) pat result_ty result_expr fail_expr
666 = match [var] [eqn_info] [] `thenDs` \ match_result ->
667 extractMatchResult match_result fail_expr
669 eqn_info = EqnInfo [pat] initial_match_result
670 initial_match_result = MatchResult CantFail
672 (\ ignore -> result_expr)
675 matchSimply scrut_expr pat result_ty result_expr msg
676 = newSysLocalDs (outPatType pat) `thenDs` \ scrut_var ->
677 matchSimply (Var scrut_var) pat result_ty result_expr msg `thenDs` \ expr ->
678 returnDs (Let (NonRec scrut_var scrut_expr) expr)
681 extractMatchResult (MatchResult CantFail _ match_fn _) fail_expr
682 = returnDs (match_fn (error "It can't fail!"))
684 extractMatchResult (MatchResult CanFail result_ty match_fn cxt) fail_expr
685 = mkFailurePair result_ty `thenDs` \ (fail_bind_fn, if_it_fails) ->
686 returnDs (Let (fail_bind_fn fail_expr) (match_fn if_it_fails))
689 %************************************************************************
691 %* flattenMatches : create a list of EquationInfo *
693 %************************************************************************
694 \subsection[flattenMatches]{@flattenMatches@: create @[EquationInfo]@}
696 This is actually local to @matchWrapper@.
701 -> [TypecheckedMatch]
702 -> DsM [EquationInfo]
704 flattenMatches kind [] = returnDs []
706 flattenMatches kind (match : matches)
707 = flatten_match [] match `thenDs` \ eqn_info ->
708 flattenMatches kind matches `thenDs` \ eqn_infos ->
709 returnDs (eqn_info : eqn_infos)
711 flatten_match :: [TypecheckedPat] -- Reversed list of patterns encountered so far
715 flatten_match pats_so_far (PatMatch pat match)
716 = flatten_match (pat:pats_so_far) match
718 flatten_match pats_so_far (GRHSMatch (GRHSsAndBindsOut grhss binds ty))
719 = dsBinds binds `thenDs` \ core_binds ->
720 dsGRHSs ty kind pats grhss `thenDs` \ match_result ->
721 returnDs (EqnInfo pats (mkCoLetsMatchResult core_binds match_result))
723 pats = reverse pats_so_far -- They've accumulated in reverse order
725 flatten_match pats_so_far (SimpleMatch expr)
726 = dsExpr expr `thenDs` \ core_expr ->
727 getSrcLocDs `thenDs` \ locn ->
728 returnDs (EqnInfo pats
729 (MatchResult CantFail (coreExprType core_expr)
730 (\ ignore -> core_expr)
731 (DsMatchContext kind pats locn)))
733 -- the matching can't fail, so we won't generate an error message.
735 pats = reverse pats_so_far -- They've accumulated in reverse order