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 )
12 import CmdLineOpts ( DynFlag(..), dopt )
14 import TcHsSyn ( TypecheckedPat, TypecheckedMatch, TypecheckedMatchContext, outPatType )
15 import Check ( check, ExhaustivePat )
17 import CoreUtils ( bindNonRec )
19 import DsGRHSs ( dsGRHSs )
21 import Id ( idType, recordSelectorFieldLabel, Id )
22 import DataCon ( dataConFieldLabels, dataConInstOrigArgTys )
23 import MatchCon ( matchConFamily )
24 import MatchLit ( matchLiterals )
25 import PrelInfo ( pAT_ERROR_ID )
26 import TcType ( mkTyVarTys, Type, tcTyConAppArgs, tcEqType )
27 import TysWiredIn ( nilDataCon, consDataCon, mkTupleTy, mkListTy,
28 tupleCon, parrFakeCon, mkPArrTy )
29 import BasicTypes ( Boxity(..) )
31 import ErrUtils ( addWarnLocHdrLine, dontAddErrLoc )
32 import Util ( lengthExceeds, isSingleton, notNull )
36 This function is a wrapper of @match@, it must be called from all the parts where
37 it was called match, but only substitutes the firs call, ....
38 if the associated flags are declared, warnings will be issued.
39 It can not be called matchWrapper because this name already exists :-(
44 matchExport :: [Id] -- Vars rep'ing the exprs we're matching with
45 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
46 -> DsM MatchResult -- Desugared result!
50 = getDOptsDs `thenDs` \ dflags ->
51 matchExport_really dflags vars qs
53 matchExport_really dflags vars qs@((EqnInfo _ ctx _ (MatchResult _ _)) : _)
54 | incomplete && shadow =
55 dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
56 dsIncompleteWarn ctx pats `thenDs` \ () ->
59 dsIncompleteWarn ctx pats `thenDs` \ () ->
62 dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
66 where (pats,indexs) = check qs
67 incomplete = dopt Opt_WarnIncompletePatterns dflags
69 shadow = dopt Opt_WarnOverlappingPatterns dflags
70 && sizeUniqSet indexs < no_eqns
72 unused_eqns = uniqSetToList (mkUniqSet [1..no_eqns] `minusUniqSet` indexs)
73 eqns_shadow = map (\n -> qs!!(n - 1)) unused_eqns
76 This variable shows the maximum number of lines of output generated for warnings.
77 It will limit the number of patterns/equations displayed to@ maximum_output@.
79 (ToDo: add command-line option?)
85 The next two functions create the warning message.
88 dsShadowWarn :: DsMatchContext -> [EquationInfo] -> DsM ()
89 dsShadowWarn ctx@(DsMatchContext kind _ _) qs = dsWarn warn
91 warn | qs `lengthExceeds` maximum_output
92 = pp_context ctx (ptext SLIT("are overlapped"))
93 (\ f -> vcat (map (ppr_eqn f kind) (take maximum_output qs)) $$
96 = pp_context ctx (ptext SLIT("are overlapped"))
97 (\ f -> vcat $ map (ppr_eqn f kind) qs)
100 dsIncompleteWarn :: DsMatchContext -> [ExhaustivePat] -> DsM ()
101 dsIncompleteWarn ctx@(DsMatchContext kind _ _) pats = dsWarn warn
103 warn = pp_context ctx (ptext SLIT("are non-exhaustive"))
104 (\f -> hang (ptext SLIT("Patterns not matched:"))
105 4 ((vcat $ map (ppr_incomplete_pats kind)
106 (take maximum_output pats))
109 dots | pats `lengthExceeds` maximum_output = ptext SLIT("...")
112 pp_context NoMatchContext msg rest_of_msg_fun
113 = dontAddErrLoc (ptext SLIT("Some match(es)") <+> hang msg 8 (rest_of_msg_fun id))
115 pp_context (DsMatchContext kind pats loc) msg rest_of_msg_fun
116 = addWarnLocHdrLine loc
117 (ptext SLIT("Pattern match(es)") <+> msg)
118 (sep [ppr_match <> char ':', nest 4 (rest_of_msg_fun pref)])
122 FunRhs fun -> (pprMatchContext kind, \ pp -> ppr fun <+> pp)
123 other -> (pprMatchContext kind <+> ppr_pats pats, \ pp -> pp)
125 ppr_pats pats = sep (map ppr pats)
127 ppr_shadow_pats kind pats
128 = sep [ppr_pats pats, matchSeparator kind, ptext SLIT("...")]
130 ppr_incomplete_pats kind (pats,[]) = ppr_pats pats
131 ppr_incomplete_pats kind (pats,constraints) =
132 sep [ppr_pats pats, ptext SLIT("with"),
133 sep (map ppr_constraint constraints)]
136 ppr_constraint (var,pats) = sep [ppr var, ptext SLIT("`notElem`"), ppr pats]
138 ppr_eqn prefixF kind (EqnInfo _ _ pats _) = prefixF (ppr_shadow_pats kind pats)
142 The function @match@ is basically the same as in the Wadler chapter,
143 except it is monadised, to carry around the name supply, info about
146 Notes on @match@'s arguments, assuming $m$ equations and $n$ patterns:
149 A list of $n$ variable names, those variables presumably bound to the
150 $n$ expressions being matched against the $n$ patterns. Using the
151 list of $n$ expressions as the first argument showed no benefit and
155 The second argument, a list giving the ``equation info'' for each of
159 the $n$ patterns for that equation, and
161 a list of Core bindings [@(Id, CoreExpr)@ pairs] to be ``stuck on
162 the front'' of the matching code, as in:
168 and finally: (ToDo: fill in)
170 The right way to think about the ``after-match function'' is that it
171 is an embryonic @CoreExpr@ with a ``hole'' at the end for the
172 final ``else expression''.
175 There is a type synonym, @EquationInfo@, defined in module @DsUtils@.
177 An experiment with re-ordering this information about equations (in
178 particular, having the patterns available in column-major order)
182 A default expression---what to evaluate if the overall pattern-match
183 fails. This expression will (almost?) always be
184 a measly expression @Var@, unless we know it will only be used once
185 (as we do in @glue_success_exprs@).
187 Leaving out this third argument to @match@ (and slamming in lots of
188 @Var "fail"@s) is a positively {\em bad} idea, because it makes it
189 impossible to share the default expressions. (Also, it stands no
190 chance of working in our post-upheaval world of @Locals@.)
192 So, the full type signature:
194 match :: [Id] -- Variables rep'ing the exprs we're matching with
195 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
196 -> DsM MatchResult -- Desugared result!
199 Note: @match@ is often called via @matchWrapper@ (end of this module),
200 a function that does much of the house-keeping that goes with a call
203 It is also worth mentioning the {\em typical} way a block of equations
204 is desugared with @match@. At each stage, it is the first column of
205 patterns that is examined. The steps carried out are roughly:
208 Tidy the patterns in column~1 with @tidyEqnInfo@ (this may add
209 bindings to the second component of the equation-info):
212 Remove the `as' patterns from column~1.
214 Make all constructor patterns in column~1 into @ConPats@, notably
215 @ListPats@ and @TuplePats@.
217 Handle any irrefutable (or ``twiddle'') @LazyPats@.
220 Now {\em unmix} the equations into {\em blocks} [w/ local function
221 @unmix_eqns@], in which the equations in a block all have variable
222 patterns in column~1, or they all have constructor patterns in ...
223 (see ``the mixture rule'' in SLPJ).
225 Call @matchEqnBlock@ on each block of equations; it will do the
226 appropriate thing for each kind of column-1 pattern, usually ending up
227 in a recursive call to @match@.
230 %************************************************************************
232 %* match: empty rule *
234 %************************************************************************
235 \subsection[Match-empty-rule]{The ``empty rule''}
237 We are a little more paranoid about the ``empty rule'' (SLPJ, p.~87)
238 than the Wadler-chapter code for @match@ (p.~93, first @match@ clause).
239 And gluing the ``success expressions'' together isn't quite so pretty.
243 = returnDs (foldr1 combineMatchResults match_results)
245 match_results = [ ASSERT( null pats) mr
246 | EqnInfo _ _ pats mr <- eqns_info ]
250 %************************************************************************
252 %* match: non-empty rule *
254 %************************************************************************
255 \subsection[Match-nonempty]{@match@ when non-empty: unmixing}
257 This (more interesting) clause of @match@ uses @tidy_and_unmix_eqns@
258 (a)~to get `as'- and `twiddle'-patterns out of the way (tidying), and
259 (b)~to do ``the mixture rule'' (SLPJ, p.~88) [which really {\em
260 un}mixes the equations], producing a list of equation-info
261 blocks, each block having as its first column of patterns either all
262 constructors, or all variables (or similar beasts), etc.
264 @match_unmixed_eqn_blks@ simply takes the place of the @foldr@ in the
265 Wadler-chapter @match@ (p.~93, last clause), and @match_unmixed_blk@
266 corresponds roughly to @matchVarCon@.
269 match vars@(v:vs) eqns_info
270 = mapDs (tidyEqnInfo v) eqns_info `thenDs` \ tidy_eqns_info ->
272 tidy_eqns_blks = unmix_eqns tidy_eqns_info
274 mapDs (matchEqnBlock vars) tidy_eqns_blks `thenDs` \ match_results ->
275 returnDs (foldr1 combineMatchResults match_results)
278 unmix_eqns [eqn] = [ [eqn] ]
279 unmix_eqns (eq1@(EqnInfo _ _ (p1:p1s) _) : eq2@(EqnInfo _ _ (p2:p2s) _) : eqs)
280 = if ( (isWildPat p1 && isWildPat p2)
281 || (isConPat p1 && isConPat p2)
282 || (isLitPat p1 && isLitPat p2) ) then
283 eq1 `tack_onto` unmixed_rest
285 [ eq1 ] : unmixed_rest
287 unmixed_rest = unmix_eqns (eq2:eqs)
289 x `tack_onto` xss = ( x : head xss) : tail xss
292 Tidy up the leftmost pattern in an @EquationInfo@, given the variable @v@
293 which will be scrutinised. This means:
296 Replace variable patterns @x@ (@x /= v@) with the pattern @_@,
297 together with the binding @x = v@.
299 Replace the `as' pattern @x@@p@ with the pattern p and a binding @x = v@.
301 Removing lazy (irrefutable) patterns (you don't want to know...).
303 Converting explicit tuple-, list-, and parallel-array-pats into ordinary
306 Convert the literal pat "" to [].
309 The result of this tidying is that the column of patterns will include
313 The @VarPat@ information isn't needed any more after this.
316 @ListPats@, @TuplePats@, etc., are all converted into @ConPats@.
318 \item[@LitPats@ and @NPats@:]
319 @LitPats@/@NPats@ of ``known friendly types'' (Int, Char,
320 Float, Double, at least) are converted to unboxed form; e.g.,
321 \tr{(NPat (HsInt i) _ _)} is converted to:
323 (ConPat I# _ _ [LitPat (HsIntPrim i) _])
328 tidyEqnInfo :: Id -> EquationInfo -> DsM EquationInfo
329 -- DsM'd because of internal call to "match".
330 -- "tidy1" does the interesting stuff, looking at
331 -- one pattern and fiddling the list of bindings.
333 -- POST CONDITION: head pattern in the EqnInfo is
342 tidyEqnInfo v (EqnInfo n ctx (pat : pats) match_result)
343 = tidy1 v pat match_result `thenDs` \ (pat', match_result') ->
344 returnDs (EqnInfo n ctx (pat' : pats) match_result')
346 -------------------------------------------------------
347 -- (pat', mr') = tidy1 v pat mr
348 -- tidies the *outer level only* of pat, giving pat'
349 -- It eliminates many pattern forms (as-patterns, variable patterns,
350 -- list patterns, etc) yielding one of:
359 tidy1 :: Id -- The Id being scrutinised
360 -> TypecheckedPat -- The pattern against which it is to be matched
361 -> MatchResult -- Current thing do do after matching
362 -> DsM (TypecheckedPat, -- Equivalent pattern
363 MatchResult) -- Augmented thing to do afterwards
364 -- The augmentation usually takes the form
365 -- of new bindings to be added to the front
367 -- case v of { x -> mr[] }
368 -- = case v of { _ -> let x=v in mr[] }
369 tidy1 v (VarPat var) match_result
370 = returnDs (WildPat (idType var), match_result')
372 match_result' | v == var = match_result
373 | otherwise = adjustMatchResult (bindNonRec var (Var v)) match_result
375 -- case v of { x@p -> mr[] }
376 -- = case v of { p -> let x=v in mr[] }
377 tidy1 v (AsPat var pat) match_result
378 = tidy1 v pat match_result'
380 match_result' | v == var = match_result
381 | otherwise = adjustMatchResult (bindNonRec var (Var v)) match_result
383 tidy1 v (WildPat ty) match_result
384 = returnDs (WildPat ty, match_result)
386 {- now, here we handle lazy patterns:
387 tidy1 v ~p bs = (v, v1 = case v of p -> v1 :
388 v2 = case v of p -> v2 : ... : bs )
390 where the v_i's are the binders in the pattern.
392 ToDo: in "v_i = ... -> v_i", are the v_i's really the same thing?
394 The case expr for v_i is just: match [v] [(p, [], \ x -> Var v_i)] any_expr
397 tidy1 v (LazyPat pat) match_result
398 = mkSelectorBinds pat (Var v) `thenDs` \ sel_binds ->
399 returnDs (WildPat (idType v),
400 mkCoLetsMatchResult [NonRec b rhs | (b,rhs) <- sel_binds] match_result)
402 -- re-express <con-something> as (ConPat ...) [directly]
404 tidy1 v (RecPat data_con pat_ty ex_tvs dicts rpats) match_result
406 = -- Special case for C {}, which can be used for
407 -- a constructor that isn't declared to have
409 returnDs (ConPat data_con pat_ty ex_tvs dicts (map WildPat con_arg_tys'), match_result)
412 = returnDs (ConPat data_con pat_ty ex_tvs dicts pats, match_result)
414 pats = map mk_pat tagged_arg_tys
416 -- Boring stuff to find the arg-tys of the constructor
417 inst_tys = tcTyConAppArgs pat_ty -- Newtypes must be opaque
418 con_arg_tys' = dataConInstOrigArgTys data_con (inst_tys ++ mkTyVarTys ex_tvs)
419 tagged_arg_tys = con_arg_tys' `zip` (dataConFieldLabels data_con)
421 -- mk_pat picks a WildPat of the appropriate type for absent fields,
422 -- and the specified pattern for present fields
423 mk_pat (arg_ty, lbl) = case [pat | (sel_id,pat,_) <- rpats,
424 recordSelectorFieldLabel sel_id == lbl
426 (pat:pats) -> ASSERT( null pats )
430 tidy1 v (ListPat ty pats) match_result
431 = returnDs (list_ConPat, match_result)
433 list_ty = mkListTy ty
435 = foldr (\ x -> \y -> ConPat consDataCon list_ty [] [] [x, y])
436 (ConPat nilDataCon list_ty [] [] [])
439 -- introduce fake parallel array constructors to be able to handle parallel
440 -- arrays with the existing machinery for constructor pattern
442 tidy1 v (PArrPat ty pats) match_result
443 = returnDs (parrConPat, match_result)
446 parrConPat = ConPat (parrFakeCon arity) (mkPArrTy ty) [] [] pats
448 tidy1 v (TuplePat pats boxity) match_result
449 = returnDs (tuple_ConPat, match_result)
453 = ConPat (tupleCon boxity arity)
454 (mkTupleTy boxity arity (map outPatType pats)) [] []
457 tidy1 v (DictPat dicts methods) match_result
458 = case num_of_d_and_ms of
459 0 -> tidy1 v (TuplePat [] Boxed) match_result
460 1 -> tidy1 v (head dict_and_method_pats) match_result
461 _ -> tidy1 v (TuplePat dict_and_method_pats Boxed) match_result
463 num_of_d_and_ms = length dicts + length methods
464 dict_and_method_pats = map VarPat (dicts ++ methods)
466 -- LitPats: we *might* be able to replace these w/ a simpler form
467 tidy1 v pat@(LitPat lit lit_ty) match_result
468 = returnDs (tidyLitPat lit pat, match_result)
470 -- NPats: we *might* be able to replace these w/ a simpler form
471 tidy1 v pat@(NPat lit lit_ty _) match_result
472 = returnDs (tidyNPat lit lit_ty pat, match_result)
474 -- and everything else goes through unchanged...
476 tidy1 v non_interesting_pat match_result
477 = returnDs (non_interesting_pat, match_result)
481 {\bf Previous @matchTwiddled@ stuff:}
483 Now we get to the only interesting part; note: there are choices for
484 translation [from Simon's notes]; translation~1:
491 s = case w of [s,t] -> s
492 t = case w of [s,t] -> t
496 Here \tr{w} is a fresh variable, and the \tr{w}-binding prevents multiple
497 evaluation of \tr{e}. An alternative translation (No.~2):
499 [ w = case e of [s,t] -> (s,t)
500 s = case w of (s,t) -> s
501 t = case w of (s,t) -> t
505 %************************************************************************
507 \subsubsection[improved-unmixing]{UNIMPLEMENTED idea for improved unmixing}
509 %************************************************************************
511 We might be able to optimise unmixing when confronted by
512 only-one-constructor-possible, of which tuples are the most notable
520 This definition would normally be unmixed into four equation blocks,
521 one per equation. But it could be unmixed into just one equation
522 block, because if the one equation matches (on the first column),
523 the others certainly will.
525 You have to be careful, though; the example
533 {\em must} be broken into two blocks at the line shown; otherwise, you
534 are forcing unnecessary evaluation. In any case, the top-left pattern
535 always gives the cue. You could then unmix blocks into groups of...
537 \item[all variables:]
539 \item[constructors or variables (mixed):]
540 Need to make sure the right names get bound for the variable patterns.
541 \item[literals or variables (mixed):]
542 Presumably just a variant on the constructor case (as it is now).
545 %************************************************************************
547 %* match on an unmixed block: the real business *
549 %************************************************************************
550 \subsection[matchEqnBlock]{@matchEqnBlock@: getting down to business}
552 The function @matchEqnBlock@ is where the matching stuff sets to
553 work a block of equations, to which the mixture rule has been applied.
554 Its arguments and results are the same as for the ``top-level'' @match@.
557 matchEqnBlock :: [Id]
561 matchEqnBlock [] _ = panic "matchEqnBlock: no names"
563 matchEqnBlock all_vars@(var:vars) eqns_info
564 | isWildPat first_pat
565 = ASSERT( all isWildPat column_1_pats ) -- Sanity check
566 -- Real true variables, just like in matchVar, SLPJ p 94
567 -- No binding to do: they'll all be wildcards by now (done in tidy)
568 match vars remaining_eqns_info
571 = ASSERT( patsAreAllCons column_1_pats )
572 matchConFamily all_vars eqns_info
575 = ASSERT( patsAreAllLits column_1_pats )
576 -- see notes in MatchLiteral
577 -- not worried about the same literal more than once in a column
578 -- (ToDo: sort this out later)
579 matchLiterals all_vars eqns_info
582 = ASSERT( isSingleton eqns_info )
583 matchSigPat all_vars (head eqns_info)
585 first_pat = head column_1_pats
586 column_1_pats = [pat | EqnInfo _ _ (pat:_) _ <- eqns_info]
587 remaining_eqns_info = [EqnInfo n ctx pats match_result | EqnInfo n ctx (_:pats) match_result <- eqns_info]
590 A SigPat is a type coercion and must be handled one at at time. We can't
591 combine them unless the type of the pattern inside is identical, and we don't
592 bother to check for that. For example:
594 data T = T1 Int | T2 Bool
595 f :: (forall a. a -> a) -> T -> t
596 f (g::Int->Int) (T1 i) = T1 (g i)
597 f (g::Bool->Bool) (T2 b) = T2 (g b)
599 We desugar this as follows:
601 f = \ g::(forall a. a->a) t::T ->
603 in case t of { T1 i -> T1 (gi i)
606 in case t of { T2 b -> T2 (gb b)
609 Note that we do not treat the first column of patterns as a
610 column of variables, because the coerced variables (gi, gb)
611 would be of different types. So we get rather grotty code.
612 But I don't think this is a common case, and if it was we could
613 doubtless improve it.
615 Meanwhile, the strategy is:
616 * treat each SigPat coercion (always non-identity coercions)
618 * deal with the stuff inside, and then wrap a binding round
619 the result to bind the new variable (gi, gb, etc)
622 matchSigPat :: [Id] -> EquationInfo -> DsM MatchResult
623 matchSigPat (var:vars) (EqnInfo n ctx (SigPat pat ty co_fn : pats) result)
624 = selectMatchVar pat `thenDs` \ new_var ->
625 dsExpr (HsApp co_fn (HsVar var)) `thenDs` \ rhs ->
626 match (new_var:vars) [EqnInfo n ctx (pat:pats) result] `thenDs` \ result' ->
627 returnDs (adjustMatchResult (bindNonRec new_var rhs) result')
630 %************************************************************************
632 %* matchWrapper: a convenient way to call @match@ *
634 %************************************************************************
635 \subsection[matchWrapper]{@matchWrapper@: a convenient interface to @match@}
637 Calls to @match@ often involve similar (non-trivial) work; that work
638 is collected here, in @matchWrapper@. This function takes as
642 Typchecked @Matches@ (of a function definition, or a case or lambda
643 expression)---the main input;
645 An error message to be inserted into any (runtime) pattern-matching
649 As results, @matchWrapper@ produces:
652 A list of variables (@Locals@) that the caller must ``promise'' to
653 bind to appropriate values; and
655 a @CoreExpr@, the desugared output (main result).
658 The main actions of @matchWrapper@ include:
661 Flatten the @[TypecheckedMatch]@ into a suitable list of
664 Create as many new variables as there are patterns in a pattern-list
665 (in any one of the @EquationInfo@s).
667 Create a suitable ``if it fails'' expression---a call to @error@ using
668 the error-string input; the {\em type} of this fail value can be found
669 by examining one of the RHS expressions in one of the @EquationInfo@s.
671 Call @match@ with all of this information!
675 matchWrapper :: TypecheckedMatchContext -- For shadowing warning messages
676 -> [TypecheckedMatch] -- Matches being desugared
677 -> DsM ([Id], CoreExpr) -- Results
680 There is one small problem with the Lambda Patterns, when somebody
681 writes something similar to:
685 he/she don't want a warning about incomplete patterns, that is done with
686 the flag @opt_WarnSimplePatterns@.
687 This problem also appears in the:
689 \item @do@ patterns, but if the @do@ can fail
690 it creates another equation if the match can fail
691 (see @DsExpr.doDo@ function)
692 \item @let@ patterns, are treated by @matchSimply@
693 List Comprension Patterns, are treated by @matchSimply@ also
696 We can't call @matchSimply@ with Lambda patterns,
697 due to the fact that lambda patterns can have more than
698 one pattern, and match simply only accepts one pattern.
703 matchWrapper ctxt matches
704 = getDOptsDs `thenDs` \ dflags ->
705 flattenMatches ctxt matches `thenDs` \ (result_ty, eqns_info) ->
707 EqnInfo _ _ arg_pats _ : _ = eqns_info
708 error_string = matchContextErrString ctxt
710 mapDs selectMatchVar arg_pats `thenDs` \ new_vars ->
711 match_fun dflags new_vars eqns_info `thenDs` \ match_result ->
713 mkErrorAppDs pAT_ERROR_ID result_ty error_string `thenDs` \ fail_expr ->
714 extractMatchResult match_result fail_expr `thenDs` \ result_expr ->
715 returnDs (new_vars, result_expr)
716 where match_fun dflags
718 LambdaExpr | dopt Opt_WarnSimplePatterns dflags -> matchExport
723 %************************************************************************
725 \subsection[matchSimply]{@matchSimply@: match a single expression against a single pattern}
727 %************************************************************************
729 @mkSimpleMatch@ is a wrapper for @match@ which deals with the
730 situation where we want to match a single expression against a single
731 pattern. It returns an expression.
734 matchSimply :: CoreExpr -- Scrutinee
735 -> TypecheckedMatchContext -- Match kind
736 -> TypecheckedPat -- Pattern it should match
737 -> CoreExpr -- Return this if it matches
738 -> CoreExpr -- Return this if it doesn't
741 matchSimply scrut kind pat result_expr fail_expr
742 = getSrcLocDs `thenDs` \ locn ->
744 ctx = DsMatchContext kind [pat] locn
745 match_result = cantFailMatchResult result_expr
747 matchSinglePat scrut ctx pat match_result `thenDs` \ match_result' ->
748 extractMatchResult match_result' fail_expr
751 matchSinglePat :: CoreExpr -> DsMatchContext -> TypecheckedPat
752 -> MatchResult -> DsM MatchResult
754 matchSinglePat (Var var) ctx pat match_result
755 = getDOptsDs `thenDs` \ dflags ->
756 match_fn dflags [var] [EqnInfo 1 ctx [pat] match_result]
759 | dopt Opt_WarnSimplePatterns dflags = matchExport
762 matchSinglePat scrut ctx pat match_result
763 = selectMatchVar pat `thenDs` \ var ->
764 matchSinglePat (Var var) ctx pat match_result `thenDs` \ match_result' ->
765 returnDs (adjustMatchResult (bindNonRec var scrut) match_result')
768 %************************************************************************
770 %* flattenMatches : create a list of EquationInfo *
772 %************************************************************************
774 \subsection[flattenMatches]{@flattenMatches@: create @[EquationInfo]@}
776 This is actually local to @matchWrapper@.
779 flattenMatches :: TypecheckedMatchContext
780 -> [TypecheckedMatch]
781 -> DsM (Type, [EquationInfo])
783 flattenMatches kind matches
784 = mapAndUnzipDs flatten_match (matches `zip` [1..]) `thenDs` \ (result_tys, eqn_infos) ->
786 result_ty = head result_tys
788 ASSERT( all (tcEqType result_ty) result_tys )
789 returnDs (result_ty, eqn_infos)
791 flatten_match (Match pats _ grhss, n)
792 = dsGRHSs kind pats grhss `thenDs` \ (ty, match_result) ->
793 getSrcLocDs `thenDs` \ locn ->
794 returnDs (ty, EqnInfo n (DsMatchContext kind pats locn) pats match_result)