2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
9 {-# OPTIONS -fno-warn-incomplete-patterns #-}
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 module Match ( match, matchEquations, matchWrapper, matchSimply, matchSinglePat ) where
18 #include "HsVersions.h"
20 import {-#SOURCE#-} DsExpr (dsLExpr)
49 This function is a wrapper of @match@, it must be called from all the parts where
50 it was called match, but only substitutes the firs call, ....
51 if the associated flags are declared, warnings will be issued.
52 It can not be called matchWrapper because this name already exists :-(
57 matchCheck :: DsMatchContext
58 -> [Id] -- Vars rep'ing the exprs we're matching with
59 -> Type -- Type of the case expression
60 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
61 -> DsM MatchResult -- Desugared result!
63 matchCheck ctx vars ty qs = do
65 matchCheck_really dflags ctx vars ty qs
67 matchCheck_really :: DynFlags
73 matchCheck_really dflags ctx vars ty qs
74 | incomplete && shadow = do
75 dsShadowWarn ctx eqns_shadow
76 dsIncompleteWarn ctx pats
79 dsIncompleteWarn ctx pats
82 dsShadowWarn ctx eqns_shadow
86 where (pats, eqns_shadow) = check qs
87 incomplete = want_incomplete && (notNull pats)
88 want_incomplete = case ctx of
89 DsMatchContext RecUpd _ ->
90 dopt Opt_WarnIncompletePatternsRecUpd dflags
92 dopt Opt_WarnIncompletePatterns dflags
93 shadow = dopt Opt_WarnOverlappingPatterns dflags
94 && not (null eqns_shadow)
97 This variable shows the maximum number of lines of output generated for warnings.
98 It will limit the number of patterns/equations displayed to@ maximum_output@.
100 (ToDo: add command-line option?)
103 maximum_output :: Int
107 The next two functions create the warning message.
110 dsShadowWarn :: DsMatchContext -> [EquationInfo] -> DsM ()
111 dsShadowWarn ctx@(DsMatchContext kind loc) qs
112 = putSrcSpanDs loc (warnDs warn)
114 warn | qs `lengthExceeds` maximum_output
115 = pp_context ctx (ptext (sLit "are overlapped"))
116 (\ f -> vcat (map (ppr_eqn f kind) (take maximum_output qs)) $$
119 = pp_context ctx (ptext (sLit "are overlapped"))
120 (\ f -> vcat $ map (ppr_eqn f kind) qs)
123 dsIncompleteWarn :: DsMatchContext -> [ExhaustivePat] -> DsM ()
124 dsIncompleteWarn ctx@(DsMatchContext kind loc) pats
125 = putSrcSpanDs loc (warnDs warn)
127 warn = pp_context ctx (ptext (sLit "are non-exhaustive"))
128 (\_ -> hang (ptext (sLit "Patterns not matched:"))
129 4 ((vcat $ map (ppr_incomplete_pats kind)
130 (take maximum_output pats))
133 dots | pats `lengthExceeds` maximum_output = ptext (sLit "...")
136 pp_context :: DsMatchContext -> SDoc -> ((SDoc -> SDoc) -> SDoc) -> SDoc
137 pp_context (DsMatchContext kind _loc) msg rest_of_msg_fun
138 = vcat [ptext (sLit "Pattern match(es)") <+> msg,
139 sep [ptext (sLit "In") <+> ppr_match <> char ':', nest 4 (rest_of_msg_fun pref)]]
143 FunRhs fun _ -> (pprMatchContext kind, \ pp -> ppr fun <+> pp)
144 _ -> (pprMatchContext kind, \ pp -> pp)
146 ppr_pats :: Outputable a => [a] -> SDoc
147 ppr_pats pats = sep (map ppr pats)
149 ppr_shadow_pats :: HsMatchContext Name -> [Pat Id] -> SDoc
150 ppr_shadow_pats kind pats
151 = sep [ppr_pats pats, matchSeparator kind, ptext (sLit "...")]
153 ppr_incomplete_pats :: HsMatchContext Name -> ExhaustivePat -> SDoc
154 ppr_incomplete_pats _ (pats,[]) = ppr_pats pats
155 ppr_incomplete_pats _ (pats,constraints) =
156 sep [ppr_pats pats, ptext (sLit "with"),
157 sep (map ppr_constraint constraints)]
159 ppr_constraint :: (Name,[HsLit]) -> SDoc
160 ppr_constraint (var,pats) = sep [ppr var, ptext (sLit "`notElem`"), ppr pats]
162 ppr_eqn :: (SDoc -> SDoc) -> HsMatchContext Name -> EquationInfo -> SDoc
163 ppr_eqn prefixF kind eqn = prefixF (ppr_shadow_pats kind (eqn_pats eqn))
167 %************************************************************************
169 The main matching function
171 %************************************************************************
173 The function @match@ is basically the same as in the Wadler chapter,
174 except it is monadised, to carry around the name supply, info about
177 Notes on @match@'s arguments, assuming $m$ equations and $n$ patterns:
180 A list of $n$ variable names, those variables presumably bound to the
181 $n$ expressions being matched against the $n$ patterns. Using the
182 list of $n$ expressions as the first argument showed no benefit and
186 The second argument, a list giving the ``equation info'' for each of
190 the $n$ patterns for that equation, and
192 a list of Core bindings [@(Id, CoreExpr)@ pairs] to be ``stuck on
193 the front'' of the matching code, as in:
199 and finally: (ToDo: fill in)
201 The right way to think about the ``after-match function'' is that it
202 is an embryonic @CoreExpr@ with a ``hole'' at the end for the
203 final ``else expression''.
206 There is a type synonym, @EquationInfo@, defined in module @DsUtils@.
208 An experiment with re-ordering this information about equations (in
209 particular, having the patterns available in column-major order)
213 A default expression---what to evaluate if the overall pattern-match
214 fails. This expression will (almost?) always be
215 a measly expression @Var@, unless we know it will only be used once
216 (as we do in @glue_success_exprs@).
218 Leaving out this third argument to @match@ (and slamming in lots of
219 @Var "fail"@s) is a positively {\em bad} idea, because it makes it
220 impossible to share the default expressions. (Also, it stands no
221 chance of working in our post-upheaval world of @Locals@.)
224 Note: @match@ is often called via @matchWrapper@ (end of this module),
225 a function that does much of the house-keeping that goes with a call
228 It is also worth mentioning the {\em typical} way a block of equations
229 is desugared with @match@. At each stage, it is the first column of
230 patterns that is examined. The steps carried out are roughly:
233 Tidy the patterns in column~1 with @tidyEqnInfo@ (this may add
234 bindings to the second component of the equation-info):
237 Remove the `as' patterns from column~1.
239 Make all constructor patterns in column~1 into @ConPats@, notably
240 @ListPats@ and @TuplePats@.
242 Handle any irrefutable (or ``twiddle'') @LazyPats@.
245 Now {\em unmix} the equations into {\em blocks} [w/ local function
246 @unmix_eqns@], in which the equations in a block all have variable
247 patterns in column~1, or they all have constructor patterns in ...
248 (see ``the mixture rule'' in SLPJ).
250 Call @matchEqnBlock@ on each block of equations; it will do the
251 appropriate thing for each kind of column-1 pattern, usually ending up
252 in a recursive call to @match@.
255 We are a little more paranoid about the ``empty rule'' (SLPJ, p.~87)
256 than the Wadler-chapter code for @match@ (p.~93, first @match@ clause).
257 And gluing the ``success expressions'' together isn't quite so pretty.
259 This (more interesting) clause of @match@ uses @tidy_and_unmix_eqns@
260 (a)~to get `as'- and `twiddle'-patterns out of the way (tidying), and
261 (b)~to do ``the mixture rule'' (SLPJ, p.~88) [which really {\em
262 un}mixes the equations], producing a list of equation-info
263 blocks, each block having as its first column of patterns either all
264 constructors, or all variables (or similar beasts), etc.
266 @match_unmixed_eqn_blks@ simply takes the place of the @foldr@ in the
267 Wadler-chapter @match@ (p.~93, last clause), and @match_unmixed_blk@
268 corresponds roughly to @matchVarCon@.
271 match :: [Id] -- Variables rep'ing the exprs we're matching with
272 -> Type -- Type of the case expression
273 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
274 -> DsM MatchResult -- Desugared result!
277 = ASSERT2( not (null eqns), ppr ty )
278 return (foldr1 combineMatchResults match_results)
280 match_results = [ ASSERT( null (eqn_pats eqn) )
284 match vars@(v:_) ty eqns
285 = ASSERT( not (null eqns ) )
286 do { -- Tidy the first pattern, generating
287 -- auxiliary bindings if necessary
288 (aux_binds, tidy_eqns) <- mapAndUnzipM (tidyEqnInfo v) eqns
290 -- Group the equations and match each group in turn
292 ; let grouped = (groupEquations tidy_eqns)
294 -- print the view patterns that are commoned up to help debug
295 ; ifOptM Opt_D_dump_view_pattern_commoning (debug grouped)
297 ; match_results <- mapM match_group grouped
298 ; return (adjustMatchResult (foldr1 (.) aux_binds) $
299 foldr1 combineMatchResults match_results) }
301 dropGroup :: [(PatGroup,EquationInfo)] -> [EquationInfo]
304 match_group :: [(PatGroup,EquationInfo)] -> DsM MatchResult
305 match_group eqns@((group,_) : _)
307 PgAny -> matchVariables vars ty (dropGroup eqns)
308 PgCon _ -> matchConFamily vars ty (subGroups eqns)
309 PgLit _ -> matchLiterals vars ty (subGroups eqns)
310 PgN _ -> matchNPats vars ty (subGroups eqns)
311 PgNpK _ -> matchNPlusKPats vars ty (dropGroup eqns)
312 PgBang -> matchBangs vars ty (dropGroup eqns)
313 PgCo _ -> matchCoercion vars ty (dropGroup eqns)
314 PgView _ _ -> matchView vars ty (dropGroup eqns)
316 -- FIXME: we should also warn about view patterns that should be
317 -- commoned up but are not
319 -- print some stuff to see what's getting grouped
320 -- use -dppr-debug to see the resolution of overloaded lits
322 let gs = map (\group -> foldr (\ (p,_) -> \acc ->
323 case p of PgView e _ -> e:acc
324 _ -> acc) [] group) eqns
325 maybeWarn [] = return ()
326 maybeWarn l = warnDs (vcat l)
328 maybeWarn $ (map (\g -> text "Putting these view expressions into the same case:" <+> (ppr g))
329 (filter (not . null) gs))
331 matchVariables :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
332 -- Real true variables, just like in matchVar, SLPJ p 94
333 -- No binding to do: they'll all be wildcards by now (done in tidy)
334 matchVariables (_:vars) ty eqns = match vars ty (shiftEqns eqns)
336 matchBangs :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
337 matchBangs (var:vars) ty eqns
338 = do { match_result <- match (var:vars) ty (map decomposeFirst_Bang eqns)
339 ; return (mkEvalMatchResult var ty match_result) }
341 matchCoercion :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
342 -- Apply the coercion to the match variable and then match that
343 matchCoercion (var:vars) ty (eqns@(eqn1:_))
344 = do { let CoPat co pat _ = firstPat eqn1
345 ; var' <- newUniqueId (idName var) (hsPatType pat)
346 ; match_result <- match (var':vars) ty (map decomposeFirst_Coercion eqns)
347 ; rhs <- dsCoercion co (return (Var var))
348 ; return (mkCoLetMatchResult (NonRec var' rhs) match_result) }
350 matchView :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
351 -- Apply the view function to the match variable and then match that
352 matchView (var:vars) ty (eqns@(eqn1:_))
353 = do { -- we could pass in the expr from the PgView,
354 -- but this needs to extract the pat anyway
355 -- to figure out the type of the fresh variable
356 let ViewPat viewExpr (L _ pat) _ = firstPat eqn1
357 -- do the rest of the compilation
358 ; var' <- newUniqueId (idName var) (hsPatType pat)
359 ; match_result <- match (var':vars) ty (map decomposeFirst_View eqns)
360 -- compile the view expressions
361 ; viewExpr' <- dsLExpr viewExpr
362 ; return (mkViewMatchResult var' viewExpr' var match_result) }
364 -- decompose the first pattern and leave the rest alone
365 decomposeFirstPat :: (Pat Id -> Pat Id) -> EquationInfo -> EquationInfo
366 decomposeFirstPat extractpat (eqn@(EqnInfo { eqn_pats = pat : pats }))
367 = eqn { eqn_pats = extractpat pat : pats}
369 decomposeFirst_Coercion, decomposeFirst_Bang, decomposeFirst_View :: EquationInfo -> EquationInfo
371 decomposeFirst_Coercion = decomposeFirstPat (\ (CoPat _ pat _) -> pat)
372 decomposeFirst_Bang = decomposeFirstPat (\ (BangPat pat ) -> unLoc pat)
373 decomposeFirst_View = decomposeFirstPat (\ (ViewPat _ pat _) -> unLoc pat)
377 %************************************************************************
381 %************************************************************************
383 Tidy up the leftmost pattern in an @EquationInfo@, given the variable @v@
384 which will be scrutinised. This means:
387 Replace variable patterns @x@ (@x /= v@) with the pattern @_@,
388 together with the binding @x = v@.
390 Replace the `as' pattern @x@@p@ with the pattern p and a binding @x = v@.
392 Removing lazy (irrefutable) patterns (you don't want to know...).
394 Converting explicit tuple-, list-, and parallel-array-pats into ordinary
397 Convert the literal pat "" to [].
400 The result of this tidying is that the column of patterns will include
404 The @VarPat@ information isn't needed any more after this.
407 @ListPats@, @TuplePats@, etc., are all converted into @ConPats@.
409 \item[@LitPats@ and @NPats@:]
410 @LitPats@/@NPats@ of ``known friendly types'' (Int, Char,
411 Float, Double, at least) are converted to unboxed form; e.g.,
412 \tr{(NPat (HsInt i) _ _)} is converted to:
414 (ConPat I# _ _ [LitPat (HsIntPrim i)])
419 tidyEqnInfo :: Id -> EquationInfo
420 -> DsM (DsWrapper, EquationInfo)
421 -- DsM'd because of internal call to dsLHsBinds
422 -- and mkSelectorBinds.
423 -- "tidy1" does the interesting stuff, looking at
424 -- one pattern and fiddling the list of bindings.
426 -- POST CONDITION: head pattern in the EqnInfo is
434 tidyEqnInfo v eqn@(EqnInfo { eqn_pats = pat : pats }) = do
435 (wrap, pat') <- tidy1 v pat
436 return (wrap, eqn { eqn_pats = do pat' : pats })
438 tidy1 :: Id -- The Id being scrutinised
439 -> Pat Id -- The pattern against which it is to be matched
440 -> DsM (DsWrapper, -- Extra bindings to do before the match
441 Pat Id) -- Equivalent pattern
443 -------------------------------------------------------
444 -- (pat', mr') = tidy1 v pat mr
445 -- tidies the *outer level only* of pat, giving pat'
446 -- It eliminates many pattern forms (as-patterns, variable patterns,
447 -- list patterns, etc) yielding one of:
454 tidy1 v (ParPat pat) = tidy1 v (unLoc pat)
455 tidy1 v (SigPatOut pat _) = tidy1 v (unLoc pat)
456 tidy1 _ (WildPat ty) = return (idDsWrapper, WildPat ty)
458 -- case v of { x -> mr[] }
459 -- = case v of { _ -> let x=v in mr[] }
461 = return (wrapBind var v, WildPat (idType var))
463 tidy1 v (VarPatOut var binds)
464 = do { prs <- dsLHsBinds binds
465 ; return (wrapBind var v . mkDsLet (Rec prs),
466 WildPat (idType var)) }
468 -- case v of { x@p -> mr[] }
469 -- = case v of { p -> let x=v in mr[] }
470 tidy1 v (AsPat (L _ var) pat)
471 = do { (wrap, pat') <- tidy1 v (unLoc pat)
472 ; return (wrapBind var v . wrap, pat') }
474 {- now, here we handle lazy patterns:
475 tidy1 v ~p bs = (v, v1 = case v of p -> v1 :
476 v2 = case v of p -> v2 : ... : bs )
478 where the v_i's are the binders in the pattern.
480 ToDo: in "v_i = ... -> v_i", are the v_i's really the same thing?
482 The case expr for v_i is just: match [v] [(p, [], \ x -> Var v_i)] any_expr
485 tidy1 v (LazyPat pat)
486 = do { sel_prs <- mkSelectorBinds pat (Var v)
487 ; let sel_binds = [NonRec b rhs | (b,rhs) <- sel_prs]
488 ; return (mkDsLets sel_binds, WildPat (idType v)) }
490 tidy1 _ (ListPat pats ty)
491 = return (idDsWrapper, unLoc list_ConPat)
493 list_ty = mkListTy ty
494 list_ConPat = foldr (\ x y -> mkPrefixConPat consDataCon [x, y] list_ty)
498 -- Introduce fake parallel array constructors to be able to handle parallel
499 -- arrays with the existing machinery for constructor pattern
500 tidy1 _ (PArrPat pats ty)
501 = return (idDsWrapper, unLoc parrConPat)
504 parrConPat = mkPrefixConPat (parrFakeCon arity) pats (mkPArrTy ty)
506 tidy1 _ (TuplePat pats boxity ty)
507 = return (idDsWrapper, unLoc tuple_ConPat)
510 tuple_ConPat = mkPrefixConPat (tupleCon boxity arity) pats ty
512 -- LitPats: we *might* be able to replace these w/ a simpler form
514 = return (idDsWrapper, tidyLitPat lit)
516 -- NPats: we *might* be able to replace these w/ a simpler form
517 tidy1 _ (NPat lit mb_neg eq)
518 = return (idDsWrapper, tidyNPat lit mb_neg eq)
520 -- Everything else goes through unchanged...
522 tidy1 _ non_interesting_pat
523 = return (idDsWrapper, non_interesting_pat)
527 {\bf Previous @matchTwiddled@ stuff:}
529 Now we get to the only interesting part; note: there are choices for
530 translation [from Simon's notes]; translation~1:
537 s = case w of [s,t] -> s
538 t = case w of [s,t] -> t
542 Here \tr{w} is a fresh variable, and the \tr{w}-binding prevents multiple
543 evaluation of \tr{e}. An alternative translation (No.~2):
545 [ w = case e of [s,t] -> (s,t)
546 s = case w of (s,t) -> s
547 t = case w of (s,t) -> t
551 %************************************************************************
553 \subsubsection[improved-unmixing]{UNIMPLEMENTED idea for improved unmixing}
555 %************************************************************************
557 We might be able to optimise unmixing when confronted by
558 only-one-constructor-possible, of which tuples are the most notable
566 This definition would normally be unmixed into four equation blocks,
567 one per equation. But it could be unmixed into just one equation
568 block, because if the one equation matches (on the first column),
569 the others certainly will.
571 You have to be careful, though; the example
579 {\em must} be broken into two blocks at the line shown; otherwise, you
580 are forcing unnecessary evaluation. In any case, the top-left pattern
581 always gives the cue. You could then unmix blocks into groups of...
583 \item[all variables:]
585 \item[constructors or variables (mixed):]
586 Need to make sure the right names get bound for the variable patterns.
587 \item[literals or variables (mixed):]
588 Presumably just a variant on the constructor case (as it is now).
591 %************************************************************************
593 %* matchWrapper: a convenient way to call @match@ *
595 %************************************************************************
596 \subsection[matchWrapper]{@matchWrapper@: a convenient interface to @match@}
598 Calls to @match@ often involve similar (non-trivial) work; that work
599 is collected here, in @matchWrapper@. This function takes as
603 Typchecked @Matches@ (of a function definition, or a case or lambda
604 expression)---the main input;
606 An error message to be inserted into any (runtime) pattern-matching
610 As results, @matchWrapper@ produces:
613 A list of variables (@Locals@) that the caller must ``promise'' to
614 bind to appropriate values; and
616 a @CoreExpr@, the desugared output (main result).
619 The main actions of @matchWrapper@ include:
622 Flatten the @[TypecheckedMatch]@ into a suitable list of
625 Create as many new variables as there are patterns in a pattern-list
626 (in any one of the @EquationInfo@s).
628 Create a suitable ``if it fails'' expression---a call to @error@ using
629 the error-string input; the {\em type} of this fail value can be found
630 by examining one of the RHS expressions in one of the @EquationInfo@s.
632 Call @match@ with all of this information!
636 matchWrapper :: HsMatchContext Name -- For shadowing warning messages
637 -> MatchGroup Id -- Matches being desugared
638 -> DsM ([Id], CoreExpr) -- Results
641 There is one small problem with the Lambda Patterns, when somebody
642 writes something similar to:
646 he/she don't want a warning about incomplete patterns, that is done with
647 the flag @opt_WarnSimplePatterns@.
648 This problem also appears in the:
650 \item @do@ patterns, but if the @do@ can fail
651 it creates another equation if the match can fail
652 (see @DsExpr.doDo@ function)
653 \item @let@ patterns, are treated by @matchSimply@
654 List Comprension Patterns, are treated by @matchSimply@ also
657 We can't call @matchSimply@ with Lambda patterns,
658 due to the fact that lambda patterns can have more than
659 one pattern, and match simply only accepts one pattern.
664 matchWrapper ctxt (MatchGroup matches match_ty)
665 = ASSERT( notNull matches )
666 do { eqns_info <- mapM mk_eqn_info matches
667 ; new_vars <- selectMatchVars arg_pats
668 ; result_expr <- matchEquations ctxt new_vars eqns_info rhs_ty
669 ; return (new_vars, result_expr) }
671 arg_pats = map unLoc (hsLMatchPats (head matches))
672 n_pats = length arg_pats
673 (_, rhs_ty) = splitFunTysN n_pats match_ty
675 mk_eqn_info (L _ (Match pats _ grhss))
676 = do { let upats = map unLoc pats
677 ; match_result <- dsGRHSs ctxt upats grhss rhs_ty
678 ; return (EqnInfo { eqn_pats = upats, eqn_rhs = match_result}) }
681 matchEquations :: HsMatchContext Name
682 -> [Id] -> [EquationInfo] -> Type
684 matchEquations ctxt vars eqns_info rhs_ty
685 = do { dflags <- getDOptsDs
686 ; locn <- getSrcSpanDs
687 ; let ds_ctxt = DsMatchContext ctxt locn
688 error_string = matchContextErrString ctxt
690 ; match_result <- match_fun dflags ds_ctxt vars rhs_ty eqns_info
692 ; fail_expr <- mkErrorAppDs pAT_ERROR_ID rhs_ty error_string
693 ; extractMatchResult match_result fail_expr }
695 match_fun dflags ds_ctxt
697 LambdaExpr | dopt Opt_WarnSimplePatterns dflags -> matchCheck ds_ctxt
699 _ -> matchCheck ds_ctxt
702 %************************************************************************
704 \subsection[matchSimply]{@matchSimply@: match a single expression against a single pattern}
706 %************************************************************************
708 @mkSimpleMatch@ is a wrapper for @match@ which deals with the
709 situation where we want to match a single expression against a single
710 pattern. It returns an expression.
713 matchSimply :: CoreExpr -- Scrutinee
714 -> HsMatchContext Name -- Match kind
715 -> LPat Id -- Pattern it should match
716 -> CoreExpr -- Return this if it matches
717 -> CoreExpr -- Return this if it doesn't
720 matchSimply scrut hs_ctx pat result_expr fail_expr = do
722 match_result = cantFailMatchResult result_expr
723 rhs_ty = exprType fail_expr
724 -- Use exprType of fail_expr, because won't refine in the case of failure!
725 match_result' <- matchSinglePat scrut hs_ctx pat rhs_ty match_result
726 extractMatchResult match_result' fail_expr
729 matchSinglePat :: CoreExpr -> HsMatchContext Name -> LPat Id
730 -> Type -> MatchResult -> DsM MatchResult
731 matchSinglePat (Var var) hs_ctx (L _ pat) ty match_result = do
736 | dopt Opt_WarnSimplePatterns dflags = matchCheck ds_ctx
739 ds_ctx = DsMatchContext hs_ctx locn
740 match_fn dflags [var] ty [EqnInfo { eqn_pats = [pat], eqn_rhs = match_result }]
742 matchSinglePat scrut hs_ctx pat ty match_result = do
743 var <- selectSimpleMatchVarL pat
744 match_result' <- matchSinglePat (Var var) hs_ctx pat ty match_result
745 return (adjustMatchResult (bindNonRec var scrut) match_result')
749 %************************************************************************
751 Pattern classification
753 %************************************************************************
757 = PgAny -- Immediate match: variables, wildcards,
759 | PgCon DataCon -- Constructor patterns (incl list, tuple)
760 | PgLit Literal -- Literal patterns
761 | PgN Literal -- Overloaded literals
762 | PgNpK Literal -- n+k patterns
763 | PgBang -- Bang patterns
764 | PgCo Type -- Coercion patterns; the type is the type
765 -- of the pattern *inside*
766 | PgView (LHsExpr Id) -- view pattern (e -> p):
767 -- the LHsExpr is the expression e
768 Type -- the Type is the type of p (equivalently, the result type of e)
770 groupEquations :: [EquationInfo] -> [[(PatGroup, EquationInfo)]]
771 -- If the result is of form [g1, g2, g3],
772 -- (a) all the (pg,eq) pairs in g1 have the same pg
773 -- (b) none of the gi are empty
775 = runs same_gp [(patGroup (firstPat eqn), eqn) | eqn <- eqns]
777 same_gp :: (PatGroup,EquationInfo) -> (PatGroup,EquationInfo) -> Bool
778 (pg1,_) `same_gp` (pg2,_) = pg1 `sameGroup` pg2
780 subGroups :: [(PatGroup, EquationInfo)] -> [[EquationInfo]]
781 -- Input is a particular group. The result sub-groups the
782 -- equations by with particular constructor, literal etc they match.
783 -- The order may be swizzled, so the matching should be order-independent
784 subGroups groups = map (map snd) (equivClasses cmp groups)
786 (pg1, _) `cmp` (pg2, _) = pg1 `cmp_pg` pg2
787 (PgCon c1) `cmp_pg` (PgCon c2) = c1 `compare` c2
788 (PgLit l1) `cmp_pg` (PgLit l2) = l1 `compare` l2
789 (PgN l1) `cmp_pg` (PgN l2) = l1 `compare` l2
790 -- These are the only cases that are every sub-grouped
792 sameGroup :: PatGroup -> PatGroup -> Bool
793 -- Same group means that a single case expression
794 -- or test will suffice to match both, *and* the order
795 -- of testing within the group is insignificant.
796 sameGroup PgAny PgAny = True
797 sameGroup PgBang PgBang = True
798 sameGroup (PgCon _) (PgCon _) = True -- One case expression
799 sameGroup (PgLit _) (PgLit _) = True -- One case expression
800 sameGroup (PgN _) (PgN _) = True -- Needs conditionals
801 sameGroup (PgNpK l1) (PgNpK l2) = l1==l2 -- Order is significant
802 -- See Note [Order of n+k]
803 sameGroup (PgCo t1) (PgCo t2) = t1 `coreEqType` t2
804 -- CoPats are in the same goup only if the type of the
805 -- enclosed pattern is the same. The patterns outside the CoPat
806 -- always have the same type, so this boils down to saying that
807 -- the two coercions are identical.
808 sameGroup (PgView e1 t1) (PgView e2 t2) = viewLExprEq (e1,t1) (e2,t2)
809 -- ViewPats are in the same gorup iff the expressions
810 -- are "equal"---conservatively, we use syntactic equality
811 sameGroup _ _ = False
813 -- an approximation of syntactic equality used for determining when view
814 -- exprs are in the same group.
815 -- this function can always safely return false;
816 -- but doing so will result in the application of the view function being repeated.
818 -- currently: compare applications of literals and variables
819 -- and anything else that we can do without involving other
820 -- HsSyn types in the recursion
822 -- NB we can't assume that the two view expressions have the same type. Consider
823 -- f (e1 -> True) = ...
824 -- f (e2 -> "hi") = ...
825 viewLExprEq :: (LHsExpr Id,Type) -> (LHsExpr Id,Type) -> Bool
826 viewLExprEq (e1,_) (e2,_) =
828 -- short name for recursive call on unLoc
829 lexp e e' = exp (unLoc e) (unLoc e')
831 -- check that two lists have the same length
832 -- and that they match up pairwise
834 lexps [] (_:_) = False
835 lexps (_:_) [] = False
836 lexps (x:xs) (y:ys) = lexp x y && lexps xs ys
838 -- conservative, in that it demands that wrappers be
839 -- syntactically identical and doesn't look under binders
841 -- coarser notions of equality are possible
842 -- (e.g., reassociating compositions,
843 -- equating different ways of writing a coercion)
844 wrap WpHole WpHole = True
845 wrap (WpCompose w1 w2) (WpCompose w1' w2') = wrap w1 w1' && wrap w2 w2'
846 wrap (WpCast c) (WpCast c') = tcEqType c c'
847 wrap (WpApp d) (WpApp d') = d == d'
848 wrap (WpTyApp t) (WpTyApp t') = tcEqType t t'
849 -- Enhancement: could implement equality for more wrappers
850 -- if it seems useful (lams and lets)
853 -- real comparison is on HsExpr's
855 exp (HsPar (L _ e)) e' = exp e e'
856 exp e (HsPar (L _ e')) = exp e e'
857 -- because the expressions do not necessarily have the same type,
858 -- we have to compare the wrappers
859 exp (HsWrap h e) (HsWrap h' e') = wrap h h' && exp e e'
860 exp (HsVar i) (HsVar i') = i == i'
861 -- the instance for IPName derives using the id, so this works if the
863 exp (HsIPVar i) (HsIPVar i') = i == i'
864 exp (HsOverLit l) (HsOverLit l') =
865 -- overloaded lits are equal if they have the same type
866 -- and the data is the same.
867 -- this is coarser than comparing the SyntaxExpr's in l and l',
868 -- which resolve the overloading (e.g., fromInteger 1),
869 -- because these expressions get written as a bunch of different variables
870 -- (presumably to improve sharing)
871 tcEqType (overLitType l) (overLitType l') && l == l'
872 -- comparing the constants seems right
873 exp (HsLit l) (HsLit l') = l == l'
874 exp (HsApp e1 e2) (HsApp e1' e2') = lexp e1 e1' && lexp e2 e2'
875 -- the fixities have been straightened out by now, so it's safe
877 exp (OpApp l o _ ri) (OpApp l' o' _ ri') =
878 lexp l l' && lexp o o' && lexp ri ri'
879 exp (NegApp e n) (NegApp e' n') = lexp e e' && exp n n'
880 exp (SectionL e1 e2) (SectionL e1' e2') =
881 lexp e1 e1' && lexp e2 e2'
882 exp (SectionR e1 e2) (SectionR e1' e2') =
883 lexp e1 e1' && lexp e2 e2'
884 exp (HsIf e e1 e2) (HsIf e' e1' e2') =
885 lexp e e' && lexp e1 e1' && lexp e2 e2'
886 exp (ExplicitList _ ls) (ExplicitList _ ls') = lexps ls ls'
887 exp (ExplicitPArr _ ls) (ExplicitPArr _ ls') = lexps ls ls'
888 exp (ExplicitTuple ls _) (ExplicitTuple ls' _) = lexps ls ls'
889 -- Enhancement: could implement equality for more expressions
890 -- if it seems useful
895 patGroup :: Pat Id -> PatGroup
896 patGroup (WildPat {}) = PgAny
897 patGroup (BangPat {}) = PgBang
898 patGroup (ConPatOut { pat_con = dc }) = PgCon (unLoc dc)
899 patGroup (LitPat lit) = PgLit (hsLitKey lit)
900 patGroup (NPat olit mb_neg _) = PgN (hsOverLitKey olit (isJust mb_neg))
901 patGroup (NPlusKPat _ olit _ _) = PgNpK (hsOverLitKey olit False)
902 patGroup (CoPat _ p _) = PgCo (hsPatType p) -- Type of innelexp pattern
903 patGroup (ViewPat expr p _) = PgView expr (hsPatType (unLoc p))
904 patGroup pat = pprPanic "patGroup" (ppr pat)
915 We can't group the first and third together, because the second may match
916 the same thing as the first. Contrast
920 where we can group the first and third. Hence we don't regard (n+1) and
921 (n+2) as part of the same group.