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 )
21 import CoreUtils ( coreExprType )
23 import DsGRHSs ( dsGRHSs )
25 import Id ( idType, recordSelectorFieldLabel, Id )
26 import DataCon ( dataConFieldLabels, dataConArgTys )
27 import MatchCon ( matchConFamily )
28 import MatchLit ( matchLiterals )
29 import PrelVals ( pAT_ERROR_ID )
30 import Type ( isUnLiftedType, splitAlgTyConApp,
33 import TysPrim ( intPrimTy, charPrimTy, floatPrimTy, doublePrimTy,
34 addrPrimTy, wordPrimTy
36 import TysWiredIn ( nilDataCon, consDataCon, mkTupleTy, mkListTy,
37 charTy, charDataCon, intTy, intDataCon,
38 floatTy, floatDataCon, doubleTy, tupleCon,
39 doubleDataCon, addrTy,
40 addrDataCon, wordTy, wordDataCon,
41 mkUnboxedTupleTy, unboxedTupleCon
44 import ErrUtils ( addErrLocHdrLine, dontAddErrLoc )
48 This function is a wrapper of @match@, it must be called from all the parts where
49 it was called match, but only substitutes the firs call, ....
50 if the associated flags are declared, warnings will be issued.
51 It can not be called matchWrapper because this name already exists :-(
56 matchExport :: [Id] -- Vars rep'ing the exprs we're matching with
57 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
58 -> DsM MatchResult -- Desugared result!
60 matchExport vars qs@((EqnInfo _ ctx _ (MatchResult _ _)) : _)
61 | incomplete && shadow =
62 dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
63 dsIncompleteWarn ctx pats `thenDs` \ () ->
66 dsIncompleteWarn ctx pats `thenDs` \ () ->
69 dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
73 where (pats,indexs) = check qs
74 incomplete = opt_WarnIncompletePatterns && (length pats /= 0)
75 shadow = opt_WarnOverlappingPatterns && sizeUniqSet indexs < no_eqns
77 unused_eqns = uniqSetToList (mkUniqSet [1..no_eqns] `minusUniqSet` indexs)
78 eqns_shadow = map (\n -> qs!!(n - 1)) unused_eqns
81 This variable shows the maximun number of lines of output generated for warnings.
82 It will limit the number of patterns/equations displayed to maximum_output.
84 (ToDo: add command-line option?)
90 The next two functions creates the warning message.
93 dsShadowWarn :: DsMatchContext -> [EquationInfo] -> DsM ()
94 dsShadowWarn ctx@(DsMatchContext kind _ _) qs = dsWarn warn
96 warn | length qs > maximum_output
97 = pp_context ctx (ptext SLIT("are overlapped"))
98 8 (\ f -> vcat (map (ppr_eqn f kind) (take maximum_output qs)) $$
101 = pp_context ctx (ptext SLIT("are overlapped"))
102 8 (\ f -> vcat $ map (ppr_eqn f kind) qs)
105 dsIncompleteWarn :: DsMatchContext -> [ExhaustivePat] -> DsM ()
106 dsIncompleteWarn ctx@(DsMatchContext kind _ _) pats = dsWarn warn
108 warn | length pats > maximum_output
109 = pp_context ctx (ptext SLIT("are non-exhaustive"))
110 8 (\ f -> hang (ptext SLIT("Patterns not recognized:"))
111 4 (vcat (map (ppr_incomplete_pats kind)
112 (take maximum_output pats))
113 $$ ptext SLIT("...")))
115 = pp_context ctx (ptext SLIT("are non-exhaustive"))
116 8 (\ f -> hang (ptext SLIT("Patterns not recognized:"))
117 4 (vcat $ map (ppr_incomplete_pats kind) pats))
119 pp_context NoMatchContext msg ind rest_of_msg_fun
120 = dontAddErrLoc "" (ptext SLIT("Some match(es)") <+> hang msg ind (rest_of_msg_fun id))
122 pp_context (DsMatchContext kind pats loc) msg ind rest_of_msg_fun
123 = case pp_match kind pats of
125 addErrLocHdrLine loc message (nest ind (rest_of_msg_fun pref))
127 message = ptext SLIT("Pattern match(es)") <+> msg <+> ppr_match <> char ':'
129 pp_match (FunMatch fun) pats
130 = let ppr_fun = ppr fun in
131 ( hsep [ptext SLIT("in the definition of function"), quotes ppr_fun]
132 , (\ x -> ppr_fun <+> x)
135 pp_match CaseMatch pats
136 = (hang (ptext SLIT("in a group of case alternatives beginning"))
141 pp_match PatBindMatch pats
142 = ( hang (ptext SLIT("in a pattern binding"))
147 pp_match LambdaMatch pats
148 = ( hang (ptext SLIT("in a lambda abstraction"))
153 pp_match DoBindMatch pats
154 = ( hang (ptext SLIT("in a `do' pattern binding"))
159 pp_match ListCompMatch pats
160 = ( hang (ptext SLIT("in a `list comprension' pattern binding"))
165 pp_match LetMatch pats
166 = ( hang (ptext SLIT("in a `let' pattern binding"))
171 ppr_pats pats = sep (map ppr pats)
173 separator (FunMatch _) = SLIT("=")
174 separator (CaseMatch) = SLIT("->")
175 separator (LambdaMatch) = SLIT("->")
176 separator (PatBindMatch) = panic "When is this used?"
177 separator (DoBindMatch) = SLIT("<-")
178 separator (ListCompMatch) = SLIT("<-")
179 separator (LetMatch) = SLIT("=")
181 ppr_shadow_pats kind pats
182 = sep [ppr_pats pats, ptext (separator kind), ptext SLIT("...")]
184 ppr_incomplete_pats kind (pats,[]) = ppr_pats pats
185 ppr_incomplete_pats kind (pats,constraints) =
186 sep [ppr_pats pats, ptext SLIT("with"),
187 sep (map ppr_constraint constraints)]
190 ppr_constraint (var,pats) = sep [ppr var, ptext SLIT("`not_elem`"), ppr pats]
192 ppr_eqn prefixF kind (EqnInfo _ _ pats _) = prefixF (ppr_shadow_pats kind pats)
196 The function @match@ is basically the same as in the Wadler chapter,
197 except it is monadised, to carry around the name supply, info about
200 Notes on @match@'s arguments, assuming $m$ equations and $n$ patterns:
203 A list of $n$ variable names, those variables presumably bound to the
204 $n$ expressions being matched against the $n$ patterns. Using the
205 list of $n$ expressions as the first argument showed no benefit and
209 The second argument, a list giving the ``equation info'' for each of
213 the $n$ patterns for that equation, and
215 a list of Core bindings [@(Id, CoreExpr)@ pairs] to be ``stuck on
216 the front'' of the matching code, as in:
222 and finally: (ToDo: fill in)
224 The right way to think about the ``after-match function'' is that it
225 is an embryonic @CoreExpr@ with a ``hole'' at the end for the
226 final ``else expression''.
229 There is a type synonym, @EquationInfo@, defined in module @DsUtils@.
231 An experiment with re-ordering this information about equations (in
232 particular, having the patterns available in column-major order)
236 A default expression---what to evaluate if the overall pattern-match
237 fails. This expression will (almost?) always be
238 a measly expression @Var@, unless we know it will only be used once
239 (as we do in @glue_success_exprs@).
241 Leaving out this third argument to @match@ (and slamming in lots of
242 @Var "fail"@s) is a positively {\em bad} idea, because it makes it
243 impossible to share the default expressions. (Also, it stands no
244 chance of working in our post-upheaval world of @Locals@.)
246 So, the full type signature:
248 match :: [Id] -- Variables rep'ing the exprs we're matching with
249 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
250 -> DsM MatchResult -- Desugared result!
253 Note: @match@ is often called via @matchWrapper@ (end of this module),
254 a function that does much of the house-keeping that goes with a call
257 It is also worth mentioning the {\em typical} way a block of equations
258 is desugared with @match@. At each stage, it is the first column of
259 patterns that is examined. The steps carried out are roughly:
262 Tidy the patterns in column~1 with @tidyEqnInfo@ (this may add
263 bindings to the second component of the equation-info):
266 Remove the `as' patterns from column~1.
268 Make all constructor patterns in column~1 into @ConPats@, notably
269 @ListPats@ and @TuplePats@.
271 Handle any irrefutable (or ``twiddle'') @LazyPats@.
274 Now {\em unmix} the equations into {\em blocks} [w/ local function
275 @unmix_eqns@], in which the equations in a block all have variable
276 patterns in column~1, or they all have constructor patterns in ...
277 (see ``the mixture rule'' in SLPJ).
279 Call @matchUnmixedEqns@ on each block of equations; it will do the
280 appropriate thing for each kind of column-1 pattern, usually ending up
281 in a recursive call to @match@.
284 %************************************************************************
286 %* match: empty rule *
288 %************************************************************************
289 \subsection[Match-empty-rule]{The ``empty rule''}
291 We are a little more paranoid about the ``empty rule'' (SLPJ, p.~87)
292 than the Wadler-chapter code for @match@ (p.~93, first @match@ clause).
293 And gluing the ``success expressions'' together isn't quite so pretty.
297 = complete_matches eqns_info
299 complete_matches [eqn]
302 complete_matches (eqn:eqns)
303 = complete_match eqn `thenDs` \ match_result1 ->
304 complete_matches eqns `thenDs` \ match_result2 ->
305 returnDs (combineMatchResults match_result1 match_result2)
307 complete_match (EqnInfo _ _ pats match_result)
308 = ASSERT( null pats )
309 returnDs match_result
312 %************************************************************************
314 %* match: non-empty rule *
316 %************************************************************************
317 \subsection[Match-nonempty]{@match@ when non-empty: unmixing}
319 This (more interesting) clause of @match@ uses @tidy_and_unmix_eqns@
320 (a)~to get `as'- and `twiddle'-patterns out of the way (tidying), and
321 (b)~to do ``the mixture rule'' (SLPJ, p.~88) [which really {\em
322 un}mixes the equations], producing a list of equation-info
323 blocks, each block having as its first column of patterns either all
324 constructors, or all variables (or similar beasts), etc.
326 @match_unmixed_eqn_blks@ simply takes the place of the @foldr@ in the
327 Wadler-chapter @match@ (p.~93, last clause), and @match_unmixed_blk@
328 corresponds roughly to @matchVarCon@.
331 match vars@(v:vs) eqns_info
332 = mapDs (tidyEqnInfo v) eqns_info `thenDs` \ tidy_eqns_info ->
334 tidy_eqns_blks = unmix_eqns tidy_eqns_info
336 match_unmixed_eqn_blks vars tidy_eqns_blks
339 unmix_eqns [eqn] = [ [eqn] ]
340 unmix_eqns (eq1@(EqnInfo _ _ (p1:p1s) _) : eq2@(EqnInfo _ _ (p2:p2s) _) : eqs)
341 = if ( (isWildPat p1 && isWildPat p2)
342 || (isConPat p1 && isConPat p2)
343 || (isLitPat p1 && isLitPat p2) ) then
344 eq1 `tack_onto` unmixed_rest
346 [ eq1 ] : unmixed_rest
348 unmixed_rest = unmix_eqns (eq2:eqs)
350 x `tack_onto` xss = ( x : head xss) : tail xss
352 -----------------------------------------------------------------------
353 -- loop through the blocks:
354 -- subsequent blocks create a "fail expr" for the first one...
355 match_unmixed_eqn_blks :: [Id]
356 -> [ [EquationInfo] ] -- List of eqn BLOCKS
359 match_unmixed_eqn_blks vars [] = panic "match_unmixed_eqn_blks"
361 match_unmixed_eqn_blks vars [eqn_blk] = matchUnmixedEqns vars eqn_blk
363 match_unmixed_eqn_blks vars (eqn_blk:eqn_blks)
364 = matchUnmixedEqns vars eqn_blk `thenDs` \ match_result1 -> -- try to match with first blk
365 match_unmixed_eqn_blks vars eqn_blks `thenDs` \ match_result2 ->
366 returnDs (combineMatchResults match_result1 match_result2)
369 Tidy up the leftmost pattern in an @EquationInfo@, given the variable @v@
370 which will be scrutinised. This means:
373 Replace variable patterns @x@ (@x /= v@) with the pattern @_@,
374 together with the binding @x = v@.
376 Replace the `as' pattern @x@@p@ with the pattern p and a binding @x = v@.
378 Removing lazy (irrefutable) patterns (you don't want to know...).
380 Converting explicit tuple- and list-pats into ordinary @ConPats@.
382 Convert the literal pat "" to [].
385 The result of this tidying is that the column of patterns will include
389 The @VarPat@ information isn't needed any more after this.
392 @ListPats@, @TuplePats@, etc., are all converted into @ConPats@.
394 \item[@LitPats@ and @NPats@:]
395 @LitPats@/@NPats@ of ``known friendly types'' (Int, Char,
396 Float, Double, at least) are converted to unboxed form; e.g.,
397 \tr{(NPat (HsInt i) _ _)} is converted to:
399 (ConPat I# _ _ [LitPat (HsIntPrim i) _])
404 tidyEqnInfo :: Id -> EquationInfo -> DsM EquationInfo
405 -- DsM'd because of internal call to "match".
406 -- "tidy1" does the interesting stuff, looking at
407 -- one pattern and fiddling the list of bindings.
409 -- POST CONDITION: head pattern in the EqnInfo is
417 tidyEqnInfo v (EqnInfo n ctx (pat : pats) match_result)
418 = tidy1 v pat match_result `thenDs` \ (pat', match_result') ->
419 returnDs (EqnInfo n ctx (pat' : pats) match_result')
421 tidy1 :: Id -- The Id being scrutinised
422 -> TypecheckedPat -- The pattern against which it is to be matched
423 -> MatchResult -- Current thing do do after matching
424 -> DsM (TypecheckedPat, -- Equivalent pattern
425 MatchResult) -- Augmented thing to do afterwards
426 -- The augmentation usually takes the form
427 -- of new bindings to be added to the front
429 tidy1 v (VarPat var) match_result
430 = returnDs (WildPat (idType var), match_result')
432 match_result' | v == var = match_result
433 | otherwise = adjustMatchResult (bindNonRec var (Var v)) match_result
435 tidy1 v (AsPat var pat) match_result
436 = tidy1 v pat match_result'
438 match_result' | v == var = match_result
439 | otherwise = adjustMatchResult (bindNonRec var (Var v)) match_result
441 tidy1 v (WildPat ty) match_result
442 = returnDs (WildPat ty, match_result)
444 {- now, here we handle lazy patterns:
445 tidy1 v ~p bs = (v, v1 = case v of p -> v1 :
446 v2 = case v of p -> v2 : ... : bs )
448 where the v_i's are the binders in the pattern.
450 ToDo: in "v_i = ... -> v_i", are the v_i's really the same thing?
452 The case expr for v_i is just: match [v] [(p, [], \ x -> Var v_i)] any_expr
455 tidy1 v (LazyPat pat) match_result
456 = mkSelectorBinds pat (Var v) `thenDs` \ sel_binds ->
457 returnDs (WildPat (idType v),
458 mkCoLetsMatchResult [NonRec b rhs | (b,rhs) <- sel_binds] match_result)
460 -- re-express <con-something> as (ConPat ...) [directly]
462 tidy1 v (RecPat data_con pat_ty tvs dicts rpats) match_result
463 = returnDs (ConPat data_con pat_ty tvs dicts pats, match_result)
465 pats = map mk_pat tagged_arg_tys
467 -- Boring stuff to find the arg-tys of the constructor
468 (_, inst_tys, _) = splitAlgTyConApp pat_ty
469 con_arg_tys' = dataConArgTys data_con inst_tys
470 tagged_arg_tys = con_arg_tys' `zip` (dataConFieldLabels data_con)
472 -- mk_pat picks a WildPat of the appropriate type for absent fields,
473 -- and the specified pattern for present fields
474 mk_pat (arg_ty, lbl) = case [pat | (sel_id,pat,_) <- rpats,
475 recordSelectorFieldLabel sel_id == lbl
477 (pat:pats) -> ASSERT( null pats )
481 tidy1 v (ListPat ty pats) match_result
482 = returnDs (list_ConPat, match_result)
484 list_ty = mkListTy ty
486 = foldr (\ x -> \y -> ConPat consDataCon list_ty [] [] [x, y])
487 (ConPat nilDataCon list_ty [] [] [])
490 tidy1 v (TuplePat pats True{-boxed-}) match_result
491 = returnDs (tuple_ConPat, match_result)
495 = ConPat (tupleCon arity)
496 (mkTupleTy arity (map outPatType pats)) [] []
499 tidy1 v (TuplePat pats False{-unboxed-}) match_result
500 = returnDs (tuple_ConPat, match_result)
504 = ConPat (unboxedTupleCon arity)
505 (mkUnboxedTupleTy arity (map outPatType pats)) [] []
508 tidy1 v (DictPat dicts methods) match_result
509 = case num_of_d_and_ms of
510 0 -> tidy1 v (TuplePat [] True) match_result
511 1 -> tidy1 v (head dict_and_method_pats) match_result
512 _ -> tidy1 v (TuplePat dict_and_method_pats True) match_result
514 num_of_d_and_ms = length dicts + length methods
515 dict_and_method_pats = map VarPat (dicts ++ methods)
518 -- deeply ugly mangling for some (common) NPats/LitPats
520 -- LitPats: the desugarer only sees these at well-known types
522 tidy1 v pat@(LitPat lit lit_ty) match_result
523 | isUnLiftedType lit_ty
524 = returnDs (pat, match_result)
527 = returnDs (ConPat charDataCon charTy [] [] [LitPat (mk_char lit) charPrimTy],
530 | otherwise = pprPanic "tidy1:LitPat:" (ppr pat)
532 mk_char (HsChar c) = HsCharPrim c
534 -- NPats: we *might* be able to replace these w/ a simpler form
537 tidy1 v pat@(NPat lit lit_ty _) match_result
538 = returnDs (better_pat, match_result)
541 | lit_ty == charTy = ConPat charDataCon lit_ty [] [] [LitPat (mk_char lit) charPrimTy]
542 | lit_ty == intTy = ConPat intDataCon lit_ty [] [] [LitPat (mk_int lit) intPrimTy]
543 | lit_ty == wordTy = ConPat wordDataCon lit_ty [] [] [LitPat (mk_word lit) wordPrimTy]
544 | lit_ty == addrTy = ConPat addrDataCon lit_ty [] [] [LitPat (mk_addr lit) addrPrimTy]
545 | lit_ty == floatTy = ConPat floatDataCon lit_ty [] [] [LitPat (mk_float lit) floatPrimTy]
546 | lit_ty == doubleTy = ConPat doubleDataCon lit_ty [] [] [LitPat (mk_double lit) doublePrimTy]
548 -- Convert the literal pattern "" to the constructor pattern [].
549 | null_str_lit lit = ConPat nilDataCon lit_ty [] [] []
553 mk_int (HsInt i) = HsIntPrim i
554 mk_int l@(HsLitLit s) = l
556 mk_char (HsChar c) = HsCharPrim c
557 mk_char l@(HsLitLit s) = l
559 mk_word l@(HsLitLit s) = l
561 mk_addr l@(HsLitLit s) = l
563 mk_float (HsInt i) = HsFloatPrim (fromInteger i)
564 mk_float (HsFrac f) = HsFloatPrim f
565 mk_float l@(HsLitLit s) = l
567 mk_double (HsInt i) = HsDoublePrim (fromInteger i)
568 mk_double (HsFrac f) = HsDoublePrim f
569 mk_double l@(HsLitLit s) = l
571 null_str_lit (HsString s) = _NULL_ s
572 null_str_lit other_lit = False
574 -- and everything else goes through unchanged...
576 tidy1 v non_interesting_pat match_result
577 = returnDs (non_interesting_pat, match_result)
580 PREVIOUS matchTwiddled STUFF:
582 Now we get to the only interesting part; note: there are choices for
583 translation [from Simon's notes]; translation~1:
590 s = case w of [s,t] -> s
591 t = case w of [s,t] -> t
595 Here \tr{w} is a fresh variable, and the \tr{w}-binding prevents multiple
596 evaluation of \tr{e}. An alternative translation (No.~2):
598 [ w = case e of [s,t] -> (s,t)
599 s = case w of (s,t) -> s
600 t = case w of (s,t) -> t
604 %************************************************************************
606 \subsubsection[improved-unmixing]{UNIMPLEMENTED idea for improved unmixing}
608 %************************************************************************
610 We might be able to optimise unmixing when confronted by
611 only-one-constructor-possible, of which tuples are the most notable
619 This definition would normally be unmixed into four equation blocks,
620 one per equation. But it could be unmixed into just one equation
621 block, because if the one equation matches (on the first column),
622 the others certainly will.
624 You have to be careful, though; the example
632 {\em must} be broken into two blocks at the line shown; otherwise, you
633 are forcing unnecessary evaluation. In any case, the top-left pattern
634 always gives the cue. You could then unmix blocks into groups of...
636 \item[all variables:]
638 \item[constructors or variables (mixed):]
639 Need to make sure the right names get bound for the variable patterns.
640 \item[literals or variables (mixed):]
641 Presumably just a variant on the constructor case (as it is now).
644 %************************************************************************
646 %* match on an unmixed block: the real business *
648 %************************************************************************
649 \subsection[matchUnmixedEqns]{@matchUnmixedEqns@: getting down to business}
651 The function @matchUnmixedEqns@ is where the matching stuff sets to
652 work a block of equations, to which the mixture rule has been applied.
653 Its arguments and results are the same as for the ``top-level'' @match@.
656 matchUnmixedEqns :: [Id]
660 matchUnmixedEqns [] _ = panic "matchUnmixedEqns: no names"
662 matchUnmixedEqns all_vars@(var:vars) eqns_info
663 | isWildPat first_pat
664 = ASSERT( all isWildPat column_1_pats ) -- Sanity check
665 -- Real true variables, just like in matchVar, SLPJ p 94
666 -- No binding to do: they'll all be wildcards by now (done in tidy)
667 match vars remaining_eqns_info
670 = ASSERT( patsAreAllCons column_1_pats )
671 matchConFamily all_vars eqns_info
674 = ASSERT( patsAreAllLits column_1_pats )
675 -- see notes in MatchLiteral
676 -- not worried about the same literal more than once in a column
677 -- (ToDo: sort this out later)
678 matchLiterals all_vars eqns_info
681 first_pat = head column_1_pats
682 column_1_pats = [pat | EqnInfo _ _ (pat:_) _ <- eqns_info]
683 remaining_eqns_info = [EqnInfo n ctx pats match_result | EqnInfo n ctx (_:pats) match_result <- eqns_info]
686 %************************************************************************
688 %* matchWrapper: a convenient way to call @match@ *
690 %************************************************************************
691 \subsection[matchWrapper]{@matchWrapper@: a convenient interface to @match@}
693 Calls to @match@ often involve similar (non-trivial) work; that work
694 is collected here, in @matchWrapper@. This function takes as
698 Typchecked @Matches@ (of a function definition, or a case or lambda
699 expression)---the main input;
701 An error message to be inserted into any (runtime) pattern-matching
705 As results, @matchWrapper@ produces:
708 A list of variables (@Locals@) that the caller must ``promise'' to
709 bind to appropriate values; and
711 a @CoreExpr@, the desugared output (main result).
714 The main actions of @matchWrapper@ include:
717 Flatten the @[TypecheckedMatch]@ into a suitable list of
720 Create as many new variables as there are patterns in a pattern-list
721 (in any one of the @EquationInfo@s).
723 Create a suitable ``if it fails'' expression---a call to @error@ using
724 the error-string input; the {\em type} of this fail value can be found
725 by examining one of the RHS expressions in one of the @EquationInfo@s.
727 Call @match@ with all of this information!
731 matchWrapper :: DsMatchKind -- For shadowing warning messages
732 -> [TypecheckedMatch] -- Matches being desugared
733 -> String -- Error message if the match fails
734 -> DsM ([Id], CoreExpr) -- Results
737 There is one small problem with the Lambda Patterns, when somebody
738 writes something similar to:
740 he/she don't want a warning about incomplete patterns, that is done with
741 the flag opt_WarnSimplePatterns.
742 This problem also appears in the :
743 do patterns, but if the do can fail it creates another equation if the match can
744 fail (see DsExpr.doDo function)
745 let patterns, are treated by matchSimply
746 List Comprension Patterns, are treated by matchSimply also
748 We can't call matchSimply with Lambda patterns, due to lambda patterns can have more than
749 one pattern, and match simply only accepts one pattern.
754 matchWrapper kind matches error_string
755 = flattenMatches kind matches `thenDs` \ (result_ty, eqns_info) ->
757 EqnInfo _ _ arg_pats _ : _ = eqns_info
759 mapDs selectMatchVar arg_pats `thenDs` \ new_vars ->
760 match_fun new_vars eqns_info `thenDs` \ match_result ->
762 mkErrorAppDs pAT_ERROR_ID result_ty error_string `thenDs` \ fail_expr ->
763 extractMatchResult match_result fail_expr `thenDs` \ result_expr ->
764 returnDs (new_vars, result_expr)
765 where match_fun = case kind of
766 LambdaMatch | opt_WarnSimplePatterns -> matchExport
771 %************************************************************************
773 \subsection[matchSimply]{@matchSimply@: match a single expression against a single pattern}
775 %************************************************************************
777 @mkSimpleMatch@ is a wrapper for @match@ which deals with the
778 situation where we want to match a single expression against a single
779 pattern. It returns an expression.
782 matchSimply :: CoreExpr -- Scrutinee
783 -> DsMatchKind -- Match kind
784 -> TypecheckedPat -- Pattern it should match
785 -> CoreExpr -- Return this if it matches
786 -> CoreExpr -- Return this if it doesn't
789 matchSimply scrut kind pat result_expr fail_expr
790 = getSrcLocDs `thenDs` \ locn ->
792 ctx = DsMatchContext kind [pat] locn
793 match_result = cantFailMatchResult result_expr
795 matchSinglePat scrut ctx pat match_result `thenDs` \ match_result' ->
796 extractMatchResult match_result' fail_expr
799 matchSinglePat :: CoreExpr -> DsMatchContext -> TypecheckedPat
800 -> MatchResult -> DsM MatchResult
802 matchSinglePat (Var var) ctx pat match_result
803 = match_fn [var] [EqnInfo 1 ctx [pat] match_result]
805 match_fn | opt_WarnSimplePatterns = matchExport
808 matchSinglePat scrut ctx pat match_result
809 = selectMatchVar pat `thenDs` \ var ->
810 matchSinglePat (Var var) ctx pat match_result `thenDs` \ match_result' ->
811 returnDs (adjustMatchResult (bindNonRec var scrut) match_result')
814 %************************************************************************
816 %* flattenMatches : create a list of EquationInfo *
818 %************************************************************************
820 \subsection[flattenMatches]{@flattenMatches@: create @[EquationInfo]@}
822 This is actually local to @matchWrapper@.
827 -> [TypecheckedMatch]
828 -> DsM (Type, [EquationInfo])
830 flattenMatches kind matches
831 = mapAndUnzipDs flatten_match (matches `zip` [1..]) `thenDs` \ (result_tys, eqn_infos) ->
833 result_ty = head result_tys
835 ASSERT( all (== result_ty) result_tys )
836 returnDs (result_ty, eqn_infos)
838 flatten_match (Match _ pats _ grhss, n)
839 = dsGRHSs kind pats grhss `thenDs` \ (ty, match_result) ->
840 getSrcLocDs `thenDs` \ locn ->
841 returnDs (ty, EqnInfo n (DsMatchContext kind pats locn) pats match_result)