2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
9 module Match ( match, matchEquations, matchWrapper, matchSimply, matchSinglePat ) where
11 #include "HsVersions.h"
13 import {-#SOURCE#-} DsExpr (dsLExpr)
41 import qualified Data.Map as Map
44 This function is a wrapper of @match@, it must be called from all the parts where
45 it was called match, but only substitutes the firs call, ....
46 if the associated flags are declared, warnings will be issued.
47 It can not be called matchWrapper because this name already exists :-(
52 matchCheck :: DsMatchContext
53 -> [Id] -- Vars rep'ing the exprs we're matching with
54 -> Type -- Type of the case expression
55 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
56 -> DsM MatchResult -- Desugared result!
58 matchCheck ctx vars ty qs = do
60 matchCheck_really dflags ctx vars ty qs
62 matchCheck_really :: DynFlags
68 matchCheck_really dflags ctx vars ty qs
69 | incomplete && shadow = do
70 dsShadowWarn ctx eqns_shadow
71 dsIncompleteWarn ctx pats
74 dsIncompleteWarn ctx pats
77 dsShadowWarn ctx eqns_shadow
81 where (pats, eqns_shadow) = check qs
82 incomplete = want_incomplete && (notNull pats)
83 want_incomplete = case ctx of
84 DsMatchContext RecUpd _ ->
85 dopt Opt_WarnIncompletePatternsRecUpd dflags
87 dopt Opt_WarnIncompletePatterns dflags
88 shadow = dopt Opt_WarnOverlappingPatterns dflags
89 && not (null eqns_shadow)
92 This variable shows the maximum number of lines of output generated for warnings.
93 It will limit the number of patterns/equations displayed to@ maximum_output@.
95 (ToDo: add command-line option?)
102 The next two functions create the warning message.
105 dsShadowWarn :: DsMatchContext -> [EquationInfo] -> DsM ()
106 dsShadowWarn ctx@(DsMatchContext kind loc) qs
107 = putSrcSpanDs loc (warnDs warn)
109 warn | qs `lengthExceeds` maximum_output
110 = pp_context ctx (ptext (sLit "are overlapped"))
111 (\ f -> vcat (map (ppr_eqn f kind) (take maximum_output qs)) $$
114 = pp_context ctx (ptext (sLit "are overlapped"))
115 (\ f -> vcat $ map (ppr_eqn f kind) qs)
118 dsIncompleteWarn :: DsMatchContext -> [ExhaustivePat] -> DsM ()
119 dsIncompleteWarn ctx@(DsMatchContext kind loc) pats
120 = putSrcSpanDs loc (warnDs warn)
122 warn = pp_context ctx (ptext (sLit "are non-exhaustive"))
123 (\_ -> hang (ptext (sLit "Patterns not matched:"))
124 4 ((vcat $ map (ppr_incomplete_pats kind)
125 (take maximum_output pats))
128 dots | pats `lengthExceeds` maximum_output = ptext (sLit "...")
131 pp_context :: DsMatchContext -> SDoc -> ((SDoc -> SDoc) -> SDoc) -> SDoc
132 pp_context (DsMatchContext kind _loc) msg rest_of_msg_fun
133 = vcat [ptext (sLit "Pattern match(es)") <+> msg,
134 sep [ptext (sLit "In") <+> ppr_match <> char ':', nest 4 (rest_of_msg_fun pref)]]
138 FunRhs fun _ -> (pprMatchContext kind, \ pp -> ppr fun <+> pp)
139 _ -> (pprMatchContext kind, \ pp -> pp)
141 ppr_pats :: Outputable a => [a] -> SDoc
142 ppr_pats pats = sep (map ppr pats)
144 ppr_shadow_pats :: HsMatchContext Name -> [Pat Id] -> SDoc
145 ppr_shadow_pats kind pats
146 = sep [ppr_pats pats, matchSeparator kind, ptext (sLit "...")]
148 ppr_incomplete_pats :: HsMatchContext Name -> ExhaustivePat -> SDoc
149 ppr_incomplete_pats _ (pats,[]) = ppr_pats pats
150 ppr_incomplete_pats _ (pats,constraints) =
151 sep [ppr_pats pats, ptext (sLit "with"),
152 sep (map ppr_constraint constraints)]
154 ppr_constraint :: (Name,[HsLit]) -> SDoc
155 ppr_constraint (var,pats) = sep [ppr var, ptext (sLit "`notElem`"), ppr pats]
157 ppr_eqn :: (SDoc -> SDoc) -> HsMatchContext Name -> EquationInfo -> SDoc
158 ppr_eqn prefixF kind eqn = prefixF (ppr_shadow_pats kind (eqn_pats eqn))
162 %************************************************************************
164 The main matching function
166 %************************************************************************
168 The function @match@ is basically the same as in the Wadler chapter,
169 except it is monadised, to carry around the name supply, info about
172 Notes on @match@'s arguments, assuming $m$ equations and $n$ patterns:
175 A list of $n$ variable names, those variables presumably bound to the
176 $n$ expressions being matched against the $n$ patterns. Using the
177 list of $n$ expressions as the first argument showed no benefit and
181 The second argument, a list giving the ``equation info'' for each of
185 the $n$ patterns for that equation, and
187 a list of Core bindings [@(Id, CoreExpr)@ pairs] to be ``stuck on
188 the front'' of the matching code, as in:
194 and finally: (ToDo: fill in)
196 The right way to think about the ``after-match function'' is that it
197 is an embryonic @CoreExpr@ with a ``hole'' at the end for the
198 final ``else expression''.
201 There is a type synonym, @EquationInfo@, defined in module @DsUtils@.
203 An experiment with re-ordering this information about equations (in
204 particular, having the patterns available in column-major order)
208 A default expression---what to evaluate if the overall pattern-match
209 fails. This expression will (almost?) always be
210 a measly expression @Var@, unless we know it will only be used once
211 (as we do in @glue_success_exprs@).
213 Leaving out this third argument to @match@ (and slamming in lots of
214 @Var "fail"@s) is a positively {\em bad} idea, because it makes it
215 impossible to share the default expressions. (Also, it stands no
216 chance of working in our post-upheaval world of @Locals@.)
219 Note: @match@ is often called via @matchWrapper@ (end of this module),
220 a function that does much of the house-keeping that goes with a call
223 It is also worth mentioning the {\em typical} way a block of equations
224 is desugared with @match@. At each stage, it is the first column of
225 patterns that is examined. The steps carried out are roughly:
228 Tidy the patterns in column~1 with @tidyEqnInfo@ (this may add
229 bindings to the second component of the equation-info):
232 Remove the `as' patterns from column~1.
234 Make all constructor patterns in column~1 into @ConPats@, notably
235 @ListPats@ and @TuplePats@.
237 Handle any irrefutable (or ``twiddle'') @LazyPats@.
240 Now {\em unmix} the equations into {\em blocks} [w\/ local function
241 @unmix_eqns@], in which the equations in a block all have variable
242 patterns in column~1, or they all have constructor patterns in ...
243 (see ``the mixture rule'' in SLPJ).
245 Call @matchEqnBlock@ on each block of equations; it will do the
246 appropriate thing for each kind of column-1 pattern, usually ending up
247 in a recursive call to @match@.
250 We are a little more paranoid about the ``empty rule'' (SLPJ, p.~87)
251 than the Wadler-chapter code for @match@ (p.~93, first @match@ clause).
252 And gluing the ``success expressions'' together isn't quite so pretty.
254 This (more interesting) clause of @match@ uses @tidy_and_unmix_eqns@
255 (a)~to get `as'- and `twiddle'-patterns out of the way (tidying), and
256 (b)~to do ``the mixture rule'' (SLPJ, p.~88) [which really {\em
257 un}mixes the equations], producing a list of equation-info
258 blocks, each block having as its first column of patterns either all
259 constructors, or all variables (or similar beasts), etc.
261 @match_unmixed_eqn_blks@ simply takes the place of the @foldr@ in the
262 Wadler-chapter @match@ (p.~93, last clause), and @match_unmixed_blk@
263 corresponds roughly to @matchVarCon@.
266 match :: [Id] -- Variables rep\'ing the exprs we\'re matching with
267 -> Type -- Type of the case expression
268 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
269 -> DsM MatchResult -- Desugared result!
272 = ASSERT2( not (null eqns), ppr ty )
273 return (foldr1 combineMatchResults match_results)
275 match_results = [ ASSERT( null (eqn_pats eqn) )
279 match vars@(v:_) ty eqns
280 = ASSERT( not (null eqns ) )
281 do { -- Tidy the first pattern, generating
282 -- auxiliary bindings if necessary
283 (aux_binds, tidy_eqns) <- mapAndUnzipM (tidyEqnInfo v) eqns
285 -- Group the equations and match each group in turn
286 ; let grouped = groupEquations tidy_eqns
288 -- print the view patterns that are commoned up to help debug
289 ; ifDOptM Opt_D_dump_view_pattern_commoning (debug grouped)
291 ; match_results <- mapM match_group grouped
292 ; return (adjustMatchResult (foldr1 (.) aux_binds) $
293 foldr1 combineMatchResults match_results) }
295 dropGroup :: [(PatGroup,EquationInfo)] -> [EquationInfo]
298 match_group :: [(PatGroup,EquationInfo)] -> DsM MatchResult
299 match_group [] = panic "match_group"
300 match_group eqns@((group,_) : _)
302 PgCon _ -> matchConFamily vars ty (subGroup [(c,e) | (PgCon c, e) <- eqns])
303 PgLit _ -> matchLiterals vars ty (subGroup [(l,e) | (PgLit l, e) <- eqns])
304 PgAny -> matchVariables vars ty (dropGroup eqns)
305 PgN _ -> matchNPats vars ty (dropGroup eqns)
306 PgNpK _ -> matchNPlusKPats vars ty (dropGroup eqns)
307 PgBang -> matchBangs vars ty (dropGroup eqns)
308 PgCo _ -> matchCoercion vars ty (dropGroup eqns)
309 PgView _ _ -> matchView vars ty (dropGroup eqns)
311 -- FIXME: we should also warn about view patterns that should be
312 -- commoned up but are not
314 -- print some stuff to see what's getting grouped
315 -- use -dppr-debug to see the resolution of overloaded lits
317 let gs = map (\group -> foldr (\ (p,_) -> \acc ->
318 case p of PgView e _ -> e:acc
319 _ -> acc) [] group) eqns
320 maybeWarn [] = return ()
321 maybeWarn l = warnDs (vcat l)
323 maybeWarn $ (map (\g -> text "Putting these view expressions into the same case:" <+> (ppr g))
324 (filter (not . null) gs))
326 matchVariables :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
327 -- Real true variables, just like in matchVar, SLPJ p 94
328 -- No binding to do: they'll all be wildcards by now (done in tidy)
329 matchVariables (_:vars) ty eqns = match vars ty (shiftEqns eqns)
330 matchVariables [] _ _ = panic "matchVariables"
332 matchBangs :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
333 matchBangs (var:vars) ty eqns
334 = do { match_result <- match (var:vars) ty $
335 map (decomposeFirstPat getBangPat) eqns
336 ; return (mkEvalMatchResult var ty match_result) }
337 matchBangs [] _ _ = panic "matchBangs"
339 matchCoercion :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
340 -- Apply the coercion to the match variable and then match that
341 matchCoercion (var:vars) ty (eqns@(eqn1:_))
342 = do { let CoPat co pat _ = firstPat eqn1
343 ; var' <- newUniqueId var (hsPatType pat)
344 ; match_result <- match (var':vars) ty $
345 map (decomposeFirstPat getCoPat) eqns
346 ; co' <- dsHsWrapper co
347 ; let rhs' = co' (Var var)
348 ; return (mkCoLetMatchResult (NonRec var' rhs') match_result) }
349 matchCoercion _ _ _ = panic "matchCoercion"
351 matchView :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
352 -- Apply the view function to the match variable and then match that
353 matchView (var:vars) ty (eqns@(eqn1:_))
354 = do { -- we could pass in the expr from the PgView,
355 -- but this needs to extract the pat anyway
356 -- to figure out the type of the fresh variable
357 let ViewPat viewExpr (L _ pat) _ = firstPat eqn1
358 -- do the rest of the compilation
359 ; var' <- newUniqueId var (hsPatType pat)
360 ; match_result <- match (var':vars) ty $
361 map (decomposeFirstPat getViewPat) eqns
362 -- compile the view expressions
363 ; viewExpr' <- dsLExpr viewExpr
364 ; return (mkViewMatchResult var' viewExpr' var match_result) }
365 matchView _ _ _ = panic "matchView"
367 -- decompose the first pattern and leave the rest alone
368 decomposeFirstPat :: (Pat Id -> Pat Id) -> EquationInfo -> EquationInfo
369 decomposeFirstPat extractpat (eqn@(EqnInfo { eqn_pats = pat : pats }))
370 = eqn { eqn_pats = extractpat pat : pats}
371 decomposeFirstPat _ _ = panic "decomposeFirstPat"
373 getCoPat, getBangPat, getViewPat :: Pat Id -> Pat Id
374 getCoPat (CoPat _ pat _) = pat
375 getCoPat _ = panic "getCoPat"
376 getBangPat (BangPat pat ) = unLoc pat
377 getBangPat _ = panic "getBangPat"
378 getViewPat (ViewPat _ pat _) = unLoc pat
379 getViewPat _ = panic "getBangPat"
382 %************************************************************************
386 %************************************************************************
388 Tidy up the leftmost pattern in an @EquationInfo@, given the variable @v@
389 which will be scrutinised. This means:
392 Replace variable patterns @x@ (@x /= v@) with the pattern @_@,
393 together with the binding @x = v@.
395 Replace the `as' pattern @x@@p@ with the pattern p and a binding @x = v@.
397 Removing lazy (irrefutable) patterns (you don't want to know...).
399 Converting explicit tuple-, list-, and parallel-array-pats into ordinary
402 Convert the literal pat "" to [].
405 The result of this tidying is that the column of patterns will include
409 The @VarPat@ information isn't needed any more after this.
412 @ListPats@, @TuplePats@, etc., are all converted into @ConPats@.
414 \item[@LitPats@ and @NPats@:]
415 @LitPats@/@NPats@ of ``known friendly types'' (Int, Char,
416 Float, Double, at least) are converted to unboxed form; e.g.,
417 \tr{(NPat (HsInt i) _ _)} is converted to:
419 (ConPat I# _ _ [LitPat (HsIntPrim i)])
424 tidyEqnInfo :: Id -> EquationInfo
425 -> DsM (DsWrapper, EquationInfo)
426 -- DsM'd because of internal call to dsLHsBinds
427 -- and mkSelectorBinds.
428 -- "tidy1" does the interesting stuff, looking at
429 -- one pattern and fiddling the list of bindings.
431 -- POST CONDITION: head pattern in the EqnInfo is
439 tidyEqnInfo _ (EqnInfo { eqn_pats = [] })
440 = panic "tidyEqnInfo"
442 tidyEqnInfo v eqn@(EqnInfo { eqn_pats = pat : pats })
443 = do { (wrap, pat') <- tidy1 v pat
444 ; return (wrap, eqn { eqn_pats = do pat' : pats }) }
446 tidy1 :: Id -- The Id being scrutinised
447 -> Pat Id -- The pattern against which it is to be matched
448 -> DsM (DsWrapper, -- Extra bindings to do before the match
449 Pat Id) -- Equivalent pattern
451 -------------------------------------------------------
452 -- (pat', mr') = tidy1 v pat mr
453 -- tidies the *outer level only* of pat, giving pat'
454 -- It eliminates many pattern forms (as-patterns, variable patterns,
455 -- list patterns, etc) yielding one of:
462 tidy1 v (ParPat pat) = tidy1 v (unLoc pat)
463 tidy1 v (SigPatOut pat _) = tidy1 v (unLoc pat)
464 tidy1 _ (WildPat ty) = return (idDsWrapper, WildPat ty)
466 -- case v of { x -> mr[] }
467 -- = case v of { _ -> let x=v in mr[] }
469 = return (wrapBind var v, WildPat (idType var))
471 -- case v of { x@p -> mr[] }
472 -- = case v of { p -> let x=v in mr[] }
473 tidy1 v (AsPat (L _ var) pat)
474 = do { (wrap, pat') <- tidy1 v (unLoc pat)
475 ; return (wrapBind var v . wrap, pat') }
477 {- now, here we handle lazy patterns:
478 tidy1 v ~p bs = (v, v1 = case v of p -> v1 :
479 v2 = case v of p -> v2 : ... : bs )
481 where the v_i's are the binders in the pattern.
483 ToDo: in "v_i = ... -> v_i", are the v_i's really the same thing?
485 The case expr for v_i is just: match [v] [(p, [], \ x -> Var v_i)] any_expr
488 tidy1 v (LazyPat pat)
489 = do { sel_prs <- mkSelectorBinds pat (Var v)
490 ; let sel_binds = [NonRec b rhs | (b,rhs) <- sel_prs]
491 ; return (mkCoreLets sel_binds, WildPat (idType v)) }
493 tidy1 _ (ListPat pats ty)
494 = return (idDsWrapper, unLoc list_ConPat)
496 list_ty = mkListTy ty
497 list_ConPat = foldr (\ x y -> mkPrefixConPat consDataCon [x, y] list_ty)
501 -- Introduce fake parallel array constructors to be able to handle parallel
502 -- arrays with the existing machinery for constructor pattern
503 tidy1 _ (PArrPat pats ty)
504 = return (idDsWrapper, unLoc parrConPat)
507 parrConPat = mkPrefixConPat (parrFakeCon arity) pats (mkPArrTy ty)
509 tidy1 _ (TuplePat pats boxity ty)
510 = return (idDsWrapper, unLoc tuple_ConPat)
513 tuple_ConPat = mkPrefixConPat (tupleCon boxity arity) pats ty
515 -- LitPats: we *might* be able to replace these w/ a simpler form
517 = return (idDsWrapper, tidyLitPat lit)
519 -- NPats: we *might* be able to replace these w/ a simpler form
520 tidy1 _ (NPat lit mb_neg eq)
521 = return (idDsWrapper, tidyNPat lit mb_neg eq)
523 -- BangPatterns: Pattern matching is already strict in constructors,
524 -- tuples etc, so the last case strips off the bang for thoses patterns.
525 tidy1 v (BangPat (L _ (LazyPat p))) = tidy1 v (BangPat p)
526 tidy1 v (BangPat (L _ (ParPat p))) = tidy1 v (BangPat p)
527 tidy1 _ p@(BangPat (L _(VarPat _))) = return (idDsWrapper, p)
528 tidy1 _ p@(BangPat (L _ (WildPat _))) = return (idDsWrapper, p)
529 tidy1 _ p@(BangPat (L _ (CoPat _ _ _))) = return (idDsWrapper, p)
530 tidy1 _ p@(BangPat (L _ (SigPatIn _ _))) = return (idDsWrapper, p)
531 tidy1 _ p@(BangPat (L _ (SigPatOut _ _))) = return (idDsWrapper, p)
532 tidy1 v (BangPat (L _ (AsPat (L _ var) pat)))
533 = do { (wrap, pat') <- tidy1 v (BangPat pat)
534 ; return (wrapBind var v . wrap, pat') }
535 tidy1 v (BangPat (L _ p)) = tidy1 v p
537 -- Everything else goes through unchanged...
539 tidy1 _ non_interesting_pat
540 = return (idDsWrapper, non_interesting_pat)
544 {\bf Previous @matchTwiddled@ stuff:}
546 Now we get to the only interesting part; note: there are choices for
547 translation [from Simon's notes]; translation~1:
554 s = case w of [s,t] -> s
555 t = case w of [s,t] -> t
559 Here \tr{w} is a fresh variable, and the \tr{w}-binding prevents multiple
560 evaluation of \tr{e}. An alternative translation (No.~2):
562 [ w = case e of [s,t] -> (s,t)
563 s = case w of (s,t) -> s
564 t = case w of (s,t) -> t
568 %************************************************************************
570 \subsubsection[improved-unmixing]{UNIMPLEMENTED idea for improved unmixing}
572 %************************************************************************
574 We might be able to optimise unmixing when confronted by
575 only-one-constructor-possible, of which tuples are the most notable
583 This definition would normally be unmixed into four equation blocks,
584 one per equation. But it could be unmixed into just one equation
585 block, because if the one equation matches (on the first column),
586 the others certainly will.
588 You have to be careful, though; the example
596 {\em must} be broken into two blocks at the line shown; otherwise, you
597 are forcing unnecessary evaluation. In any case, the top-left pattern
598 always gives the cue. You could then unmix blocks into groups of...
600 \item[all variables:]
602 \item[constructors or variables (mixed):]
603 Need to make sure the right names get bound for the variable patterns.
604 \item[literals or variables (mixed):]
605 Presumably just a variant on the constructor case (as it is now).
608 %************************************************************************
610 %* matchWrapper: a convenient way to call @match@ *
612 %************************************************************************
613 \subsection[matchWrapper]{@matchWrapper@: a convenient interface to @match@}
615 Calls to @match@ often involve similar (non-trivial) work; that work
616 is collected here, in @matchWrapper@. This function takes as
620 Typchecked @Matches@ (of a function definition, or a case or lambda
621 expression)---the main input;
623 An error message to be inserted into any (runtime) pattern-matching
627 As results, @matchWrapper@ produces:
630 A list of variables (@Locals@) that the caller must ``promise'' to
631 bind to appropriate values; and
633 a @CoreExpr@, the desugared output (main result).
636 The main actions of @matchWrapper@ include:
639 Flatten the @[TypecheckedMatch]@ into a suitable list of
642 Create as many new variables as there are patterns in a pattern-list
643 (in any one of the @EquationInfo@s).
645 Create a suitable ``if it fails'' expression---a call to @error@ using
646 the error-string input; the {\em type} of this fail value can be found
647 by examining one of the RHS expressions in one of the @EquationInfo@s.
649 Call @match@ with all of this information!
653 matchWrapper :: HsMatchContext Name -- For shadowing warning messages
654 -> MatchGroup Id -- Matches being desugared
655 -> DsM ([Id], CoreExpr) -- Results
658 There is one small problem with the Lambda Patterns, when somebody
659 writes something similar to:
663 he/she don't want a warning about incomplete patterns, that is done with
664 the flag @opt_WarnSimplePatterns@.
665 This problem also appears in the:
667 \item @do@ patterns, but if the @do@ can fail
668 it creates another equation if the match can fail
669 (see @DsExpr.doDo@ function)
670 \item @let@ patterns, are treated by @matchSimply@
671 List Comprension Patterns, are treated by @matchSimply@ also
674 We can't call @matchSimply@ with Lambda patterns,
675 due to the fact that lambda patterns can have more than
676 one pattern, and match simply only accepts one pattern.
681 matchWrapper ctxt (MatchGroup matches match_ty)
682 = ASSERT( notNull matches )
683 do { eqns_info <- mapM mk_eqn_info matches
684 ; new_vars <- selectMatchVars arg_pats
685 ; result_expr <- matchEquations ctxt new_vars eqns_info rhs_ty
686 ; return (new_vars, result_expr) }
688 arg_pats = map unLoc (hsLMatchPats (head matches))
689 n_pats = length arg_pats
690 (_, rhs_ty) = splitFunTysN n_pats match_ty
692 mk_eqn_info (L _ (Match pats _ grhss))
693 = do { let upats = map unLoc pats
694 ; match_result <- dsGRHSs ctxt upats grhss rhs_ty
695 ; return (EqnInfo { eqn_pats = upats, eqn_rhs = match_result}) }
698 matchEquations :: HsMatchContext Name
699 -> [Id] -> [EquationInfo] -> Type
701 matchEquations ctxt vars eqns_info rhs_ty
702 = do { locn <- getSrcSpanDs
703 ; let ds_ctxt = DsMatchContext ctxt locn
704 error_doc = matchContextErrString ctxt
706 ; match_result <- matchCheck ds_ctxt vars rhs_ty eqns_info
708 ; fail_expr <- mkErrorAppDs pAT_ERROR_ID rhs_ty error_doc
709 ; extractMatchResult match_result fail_expr }
712 %************************************************************************
714 \subsection[matchSimply]{@matchSimply@: match a single expression against a single pattern}
716 %************************************************************************
718 @mkSimpleMatch@ is a wrapper for @match@ which deals with the
719 situation where we want to match a single expression against a single
720 pattern. It returns an expression.
723 matchSimply :: CoreExpr -- Scrutinee
724 -> HsMatchContext Name -- Match kind
725 -> LPat Id -- Pattern it should match
726 -> CoreExpr -- Return this if it matches
727 -> CoreExpr -- Return this if it doesn't
729 -- Do not warn about incomplete patterns; see matchSinglePat comments
730 matchSimply scrut hs_ctx pat result_expr fail_expr = do
732 match_result = cantFailMatchResult result_expr
733 rhs_ty = exprType fail_expr
734 -- Use exprType of fail_expr, because won't refine in the case of failure!
735 match_result' <- matchSinglePat scrut hs_ctx pat rhs_ty match_result
736 extractMatchResult match_result' fail_expr
739 matchSinglePat :: CoreExpr -> HsMatchContext Name -> LPat Id
740 -> Type -> MatchResult -> DsM MatchResult
741 -- Do not warn about incomplete patterns
742 -- Used for things like [ e | pat <- stuff ], where
743 -- incomplete patterns are just fine
744 matchSinglePat (Var var) _ (L _ pat) ty match_result
745 = match [var] ty [EqnInfo { eqn_pats = [pat], eqn_rhs = match_result }]
747 matchSinglePat scrut hs_ctx pat ty match_result = do
748 var <- selectSimpleMatchVarL pat
749 match_result' <- matchSinglePat (Var var) hs_ctx pat ty match_result
750 return (adjustMatchResult (bindNonRec var scrut) match_result')
754 %************************************************************************
756 Pattern classification
758 %************************************************************************
762 = PgAny -- Immediate match: variables, wildcards,
764 | PgCon DataCon -- Constructor patterns (incl list, tuple)
765 | PgLit Literal -- Literal patterns
766 | PgN Literal -- Overloaded literals
767 | PgNpK Literal -- n+k patterns
768 | PgBang -- Bang patterns
769 | PgCo Type -- Coercion patterns; the type is the type
770 -- of the pattern *inside*
771 | PgView (LHsExpr Id) -- view pattern (e -> p):
772 -- the LHsExpr is the expression e
773 Type -- the Type is the type of p (equivalently, the result type of e)
775 groupEquations :: [EquationInfo] -> [[(PatGroup, EquationInfo)]]
776 -- If the result is of form [g1, g2, g3],
777 -- (a) all the (pg,eq) pairs in g1 have the same pg
778 -- (b) none of the gi are empty
779 -- The ordering of equations is unchanged
781 = runs same_gp [(patGroup (firstPat eqn), eqn) | eqn <- eqns]
783 same_gp :: (PatGroup,EquationInfo) -> (PatGroup,EquationInfo) -> Bool
784 (pg1,_) `same_gp` (pg2,_) = pg1 `sameGroup` pg2
786 subGroup :: Ord a => [(a, EquationInfo)] -> [[EquationInfo]]
787 -- Input is a particular group. The result sub-groups the
788 -- equations by with particular constructor, literal etc they match.
789 -- Each sub-list in the result has the same PatGroup
790 -- See Note [Take care with pattern order]
792 = map reverse $ Map.elems $ foldl accumulate Map.empty group
794 accumulate pg_map (pg, eqn)
795 = case Map.lookup pg pg_map of
796 Just eqns -> Map.insert pg (eqn:eqns) pg_map
797 Nothing -> Map.insert pg [eqn] pg_map
799 -- pg_map :: Map a [EquationInfo]
800 -- Equations seen so far in reverse order of appearance
803 Note [Take care with pattern order]
804 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
805 In the subGroup function we must be very careful about pattern re-ordering,
806 Consider the patterns [ (True, Nothing), (False, x), (True, y) ]
807 Then in bringing together the patterns for True, we must not
808 swap the Nothing and y!
812 sameGroup :: PatGroup -> PatGroup -> Bool
813 -- Same group means that a single case expression
814 -- or test will suffice to match both, *and* the order
815 -- of testing within the group is insignificant.
816 sameGroup PgAny PgAny = True
817 sameGroup PgBang PgBang = True
818 sameGroup (PgCon _) (PgCon _) = True -- One case expression
819 sameGroup (PgLit _) (PgLit _) = True -- One case expression
820 sameGroup (PgN l1) (PgN l2) = l1==l2 -- Order is significant
821 sameGroup (PgNpK l1) (PgNpK l2) = l1==l2 -- See Note [Grouping overloaded literal patterns]
822 sameGroup (PgCo t1) (PgCo t2) = t1 `coreEqType` t2
823 -- CoPats are in the same goup only if the type of the
824 -- enclosed pattern is the same. The patterns outside the CoPat
825 -- always have the same type, so this boils down to saying that
826 -- the two coercions are identical.
827 sameGroup (PgView e1 t1) (PgView e2 t2) = viewLExprEq (e1,t1) (e2,t2)
828 -- ViewPats are in the same gorup iff the expressions
829 -- are "equal"---conservatively, we use syntactic equality
830 sameGroup _ _ = False
832 -- An approximation of syntactic equality used for determining when view
833 -- exprs are in the same group.
834 -- This function can always safely return false;
835 -- but doing so will result in the application of the view function being repeated.
837 -- Currently: compare applications of literals and variables
838 -- and anything else that we can do without involving other
839 -- HsSyn types in the recursion
841 -- NB we can't assume that the two view expressions have the same type. Consider
842 -- f (e1 -> True) = ...
843 -- f (e2 -> "hi") = ...
844 viewLExprEq :: (LHsExpr Id,Type) -> (LHsExpr Id,Type) -> Bool
845 viewLExprEq (e1,_) (e2,_) = lexp e1 e2
847 lexp :: LHsExpr Id -> LHsExpr Id -> Bool
848 lexp e e' = exp (unLoc e) (unLoc e')
851 exp :: HsExpr Id -> HsExpr Id -> Bool
852 -- real comparison is on HsExpr's
854 exp (HsPar (L _ e)) e' = exp e e'
855 exp e (HsPar (L _ e')) = exp e e'
856 -- because the expressions do not necessarily have the same type,
857 -- we have to compare the wrappers
858 exp (HsWrap h e) (HsWrap h' e') = wrap h h' && exp e e'
859 exp (HsVar i) (HsVar i') = i == i'
860 -- the instance for IPName derives using the id, so this works if the
862 exp (HsIPVar i) (HsIPVar i') = i == i'
863 exp (HsOverLit l) (HsOverLit l') =
864 -- Overloaded lits are equal if they have the same type
865 -- and the data is the same.
866 -- this is coarser than comparing the SyntaxExpr's in l and l',
867 -- which resolve the overloading (e.g., fromInteger 1),
868 -- because these expressions get written as a bunch of different variables
869 -- (presumably to improve sharing)
870 tcEqType (overLitType l) (overLitType l') && l == l'
871 exp (HsApp e1 e2) (HsApp e1' e2') = lexp e1 e1' && lexp e2 e2'
872 -- the fixities have been straightened out by now, so it's safe
874 exp (OpApp l o _ ri) (OpApp l' o' _ ri') =
875 lexp l l' && lexp o o' && lexp ri ri'
876 exp (NegApp e n) (NegApp e' n') = lexp e e' && exp n n'
877 exp (SectionL e1 e2) (SectionL e1' e2') =
878 lexp e1 e1' && lexp e2 e2'
879 exp (SectionR e1 e2) (SectionR e1' e2') =
880 lexp e1 e1' && lexp e2 e2'
881 exp (ExplicitTuple es1 _) (ExplicitTuple es2 _) =
882 eq_list tup_arg es1 es2
883 exp (HsIf _ e e1 e2) (HsIf _ e' e1' e2') =
884 lexp e e' && lexp e1 e1' && lexp e2 e2'
886 -- Enhancement: could implement equality for more expressions
887 -- if it seems useful
888 -- But no need for HsLit, ExplicitList, ExplicitTuple,
889 -- because they cannot be functions
893 tup_arg (Present e1) (Present e2) = lexp e1 e2
894 tup_arg (Missing t1) (Missing t2) = tcEqType t1 t2
898 wrap :: HsWrapper -> HsWrapper -> Bool
899 -- Conservative, in that it demands that wrappers be
900 -- syntactically identical and doesn't look under binders
902 -- Coarser notions of equality are possible
903 -- (e.g., reassociating compositions,
904 -- equating different ways of writing a coercion)
905 wrap WpHole WpHole = True
906 wrap (WpCompose w1 w2) (WpCompose w1' w2') = wrap w1 w1' && wrap w2 w2'
907 wrap (WpCast c) (WpCast c') = tcEqType c c'
908 wrap (WpEvApp et1) (WpEvApp et2) = ev_term et1 et2
909 wrap (WpTyApp t) (WpTyApp t') = tcEqType t t'
910 -- Enhancement: could implement equality for more wrappers
911 -- if it seems useful (lams and lets)
915 ev_term :: EvTerm -> EvTerm -> Bool
916 ev_term (EvId a) (EvId b) = a==b
917 ev_term (EvCoercion a) (EvCoercion b) = tcEqType a b
921 eq_list :: (a->a->Bool) -> [a] -> [a] -> Bool
922 eq_list _ [] [] = True
923 eq_list _ [] (_:_) = False
924 eq_list _ (_:_) [] = False
925 eq_list eq (x:xs) (y:ys) = eq x y && eq_list eq xs ys
927 patGroup :: Pat Id -> PatGroup
928 patGroup (WildPat {}) = PgAny
929 patGroup (BangPat {}) = PgBang
930 patGroup (ConPatOut { pat_con = dc }) = PgCon (unLoc dc)
931 patGroup (LitPat lit) = PgLit (hsLitKey lit)
932 patGroup (NPat olit mb_neg _) = PgN (hsOverLitKey olit (isJust mb_neg))
933 patGroup (NPlusKPat _ olit _ _) = PgNpK (hsOverLitKey olit False)
934 patGroup (CoPat _ p _) = PgCo (hsPatType p) -- Type of innelexp pattern
935 patGroup (ViewPat expr p _) = PgView expr (hsPatType (unLoc p))
936 patGroup pat = pprPanic "patGroup" (ppr pat)
939 Note [Grouping overloaded literal patterns]
940 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
947 We can't group the first and third together, because the second may match
948 the same thing as the first. Same goes for *overloaded* literal patterns
952 If the first arg matches '1' but the second does not match 'True', we
953 cannot jump to the third equation! Because the same argument might
955 Hence we don't regard 1 and 2, or (n+1) and (n+2), as part of the same group.