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)
42 import Control.Monad( when )
43 import qualified Data.Map as Map
46 This function is a wrapper of @match@, it must be called from all the parts where
47 it was called match, but only substitutes the firs call, ....
48 if the associated flags are declared, warnings will be issued.
49 It can not be called matchWrapper because this name already exists :-(
54 matchCheck :: DsMatchContext
55 -> [Id] -- Vars rep'ing the exprs we're matching with
56 -> Type -- Type of the case expression
57 -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
58 -> DsM MatchResult -- Desugared result!
60 matchCheck ctx vars ty qs
61 = do { dflags <- getDOptsDs
62 ; matchCheck_really dflags ctx vars ty qs }
64 matchCheck_really :: DynFlags
70 matchCheck_really dflags ctx@(DsMatchContext hs_ctx _) vars ty qs
71 = do { when shadow (dsShadowWarn ctx eqns_shadow)
72 ; when incomplete (dsIncompleteWarn ctx pats)
75 (pats, eqns_shadow) = check qs
76 incomplete = incomplete_flag hs_ctx && (notNull pats)
77 shadow = dopt Opt_WarnOverlappingPatterns dflags
78 && notNull eqns_shadow
80 incomplete_flag :: HsMatchContext id -> Bool
81 incomplete_flag (FunRhs {}) = dopt Opt_WarnIncompletePatterns dflags
82 incomplete_flag CaseAlt = dopt Opt_WarnIncompletePatterns dflags
84 incomplete_flag LambdaExpr = dopt Opt_WarnIncompleteUniPatterns dflags
85 incomplete_flag PatBindRhs = dopt Opt_WarnIncompleteUniPatterns dflags
86 incomplete_flag ProcExpr = dopt Opt_WarnIncompleteUniPatterns dflags
88 incomplete_flag RecUpd = dopt Opt_WarnIncompletePatternsRecUpd dflags
90 incomplete_flag ThPatQuote = False
91 incomplete_flag (StmtCtxt {}) = False -- Don't warn about incomplete patterns
92 -- in list comprehensions, pattern guards
93 -- etc. They are often *supposed* to be
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
291 ; let grouped = groupEquations tidy_eqns
293 -- print the view patterns that are commoned up to help debug
294 ; ifDOptM Opt_D_dump_view_pattern_commoning (debug grouped)
296 ; match_results <- mapM match_group grouped
297 ; return (adjustMatchResult (foldr1 (.) aux_binds) $
298 foldr1 combineMatchResults match_results) }
300 dropGroup :: [(PatGroup,EquationInfo)] -> [EquationInfo]
303 match_group :: [(PatGroup,EquationInfo)] -> DsM MatchResult
304 match_group [] = panic "match_group"
305 match_group eqns@((group,_) : _)
307 PgCon _ -> matchConFamily vars ty (subGroup [(c,e) | (PgCon c, e) <- eqns])
308 PgLit _ -> matchLiterals vars ty (subGroup [(l,e) | (PgLit l, e) <- eqns])
309 PgAny -> matchVariables vars ty (dropGroup eqns)
310 PgN _ -> matchNPats vars ty (dropGroup 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)
335 matchVariables [] _ _ = panic "matchVariables"
337 matchBangs :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
338 matchBangs (var:vars) ty eqns
339 = do { match_result <- match (var:vars) ty $
340 map (decomposeFirstPat getBangPat) eqns
341 ; return (mkEvalMatchResult var ty match_result) }
342 matchBangs [] _ _ = panic "matchBangs"
344 matchCoercion :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
345 -- Apply the coercion to the match variable and then match that
346 matchCoercion (var:vars) ty (eqns@(eqn1:_))
347 = do { let CoPat co pat _ = firstPat eqn1
348 ; var' <- newUniqueId var (hsPatType pat)
349 ; match_result <- match (var':vars) ty $
350 map (decomposeFirstPat getCoPat) eqns
351 ; co' <- dsHsWrapper co
352 ; let rhs' = co' (Var var)
353 ; return (mkCoLetMatchResult (NonRec var' rhs') match_result) }
354 matchCoercion _ _ _ = panic "matchCoercion"
356 matchView :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult
357 -- Apply the view function to the match variable and then match that
358 matchView (var:vars) ty (eqns@(eqn1:_))
359 = do { -- we could pass in the expr from the PgView,
360 -- but this needs to extract the pat anyway
361 -- to figure out the type of the fresh variable
362 let ViewPat viewExpr (L _ pat) _ = firstPat eqn1
363 -- do the rest of the compilation
364 ; var' <- newUniqueId var (hsPatType pat)
365 ; match_result <- match (var':vars) ty $
366 map (decomposeFirstPat getViewPat) eqns
367 -- compile the view expressions
368 ; viewExpr' <- dsLExpr viewExpr
369 ; return (mkViewMatchResult var' viewExpr' var match_result) }
370 matchView _ _ _ = panic "matchView"
372 -- decompose the first pattern and leave the rest alone
373 decomposeFirstPat :: (Pat Id -> Pat Id) -> EquationInfo -> EquationInfo
374 decomposeFirstPat extractpat (eqn@(EqnInfo { eqn_pats = pat : pats }))
375 = eqn { eqn_pats = extractpat pat : pats}
376 decomposeFirstPat _ _ = panic "decomposeFirstPat"
378 getCoPat, getBangPat, getViewPat :: Pat Id -> Pat Id
379 getCoPat (CoPat _ pat _) = pat
380 getCoPat _ = panic "getCoPat"
381 getBangPat (BangPat pat ) = unLoc pat
382 getBangPat _ = panic "getBangPat"
383 getViewPat (ViewPat _ pat _) = unLoc pat
384 getViewPat _ = panic "getBangPat"
387 %************************************************************************
391 %************************************************************************
393 Tidy up the leftmost pattern in an @EquationInfo@, given the variable @v@
394 which will be scrutinised. This means:
397 Replace variable patterns @x@ (@x /= v@) with the pattern @_@,
398 together with the binding @x = v@.
400 Replace the `as' pattern @x@@p@ with the pattern p and a binding @x = v@.
402 Removing lazy (irrefutable) patterns (you don't want to know...).
404 Converting explicit tuple-, list-, and parallel-array-pats into ordinary
407 Convert the literal pat "" to [].
410 The result of this tidying is that the column of patterns will include
414 The @VarPat@ information isn't needed any more after this.
417 @ListPats@, @TuplePats@, etc., are all converted into @ConPats@.
419 \item[@LitPats@ and @NPats@:]
420 @LitPats@/@NPats@ of ``known friendly types'' (Int, Char,
421 Float, Double, at least) are converted to unboxed form; e.g.,
422 \tr{(NPat (HsInt i) _ _)} is converted to:
424 (ConPat I# _ _ [LitPat (HsIntPrim i)])
429 tidyEqnInfo :: Id -> EquationInfo
430 -> DsM (DsWrapper, EquationInfo)
431 -- DsM'd because of internal call to dsLHsBinds
432 -- and mkSelectorBinds.
433 -- "tidy1" does the interesting stuff, looking at
434 -- one pattern and fiddling the list of bindings.
436 -- POST CONDITION: head pattern in the EqnInfo is
444 tidyEqnInfo _ (EqnInfo { eqn_pats = [] })
445 = panic "tidyEqnInfo"
447 tidyEqnInfo v eqn@(EqnInfo { eqn_pats = pat : pats })
448 = do { (wrap, pat') <- tidy1 v pat
449 ; return (wrap, eqn { eqn_pats = do pat' : pats }) }
451 tidy1 :: Id -- The Id being scrutinised
452 -> Pat Id -- The pattern against which it is to be matched
453 -> DsM (DsWrapper, -- Extra bindings to do before the match
454 Pat Id) -- Equivalent pattern
456 -------------------------------------------------------
457 -- (pat', mr') = tidy1 v pat mr
458 -- tidies the *outer level only* of pat, giving pat'
459 -- It eliminates many pattern forms (as-patterns, variable patterns,
460 -- list patterns, etc) yielding one of:
467 tidy1 v (ParPat pat) = tidy1 v (unLoc pat)
468 tidy1 v (SigPatOut pat _) = tidy1 v (unLoc pat)
469 tidy1 _ (WildPat ty) = return (idDsWrapper, WildPat ty)
471 -- case v of { x -> mr[] }
472 -- = case v of { _ -> let x=v in mr[] }
474 = return (wrapBind var v, WildPat (idType var))
476 -- case v of { x@p -> mr[] }
477 -- = case v of { p -> let x=v in mr[] }
478 tidy1 v (AsPat (L _ var) pat)
479 = do { (wrap, pat') <- tidy1 v (unLoc pat)
480 ; return (wrapBind var v . wrap, pat') }
482 {- now, here we handle lazy patterns:
483 tidy1 v ~p bs = (v, v1 = case v of p -> v1 :
484 v2 = case v of p -> v2 : ... : bs )
486 where the v_i's are the binders in the pattern.
488 ToDo: in "v_i = ... -> v_i", are the v_i's really the same thing?
490 The case expr for v_i is just: match [v] [(p, [], \ x -> Var v_i)] any_expr
493 tidy1 v (LazyPat pat)
494 = do { sel_prs <- mkSelectorBinds pat (Var v)
495 ; let sel_binds = [NonRec b rhs | (b,rhs) <- sel_prs]
496 ; return (mkCoreLets sel_binds, WildPat (idType v)) }
498 tidy1 _ (ListPat pats ty)
499 = return (idDsWrapper, unLoc list_ConPat)
501 list_ty = mkListTy ty
502 list_ConPat = foldr (\ x y -> mkPrefixConPat consDataCon [x, y] list_ty)
506 -- Introduce fake parallel array constructors to be able to handle parallel
507 -- arrays with the existing machinery for constructor pattern
508 tidy1 _ (PArrPat pats ty)
509 = return (idDsWrapper, unLoc parrConPat)
512 parrConPat = mkPrefixConPat (parrFakeCon arity) pats (mkPArrTy ty)
514 tidy1 _ (TuplePat pats boxity ty)
515 = return (idDsWrapper, unLoc tuple_ConPat)
518 tuple_ConPat = mkPrefixConPat (tupleCon boxity arity) pats ty
520 -- LitPats: we *might* be able to replace these w/ a simpler form
522 = return (idDsWrapper, tidyLitPat lit)
524 -- NPats: we *might* be able to replace these w/ a simpler form
525 tidy1 _ (NPat lit mb_neg eq)
526 = return (idDsWrapper, tidyNPat tidyLitPat lit mb_neg eq)
528 -- BangPatterns: Pattern matching is already strict in constructors,
529 -- tuples etc, so the last case strips off the bang for thoses patterns.
530 tidy1 v (BangPat (L _ (LazyPat p))) = tidy1 v (BangPat p)
531 tidy1 v (BangPat (L _ (ParPat p))) = tidy1 v (BangPat p)
532 tidy1 _ p@(BangPat (L _(VarPat _))) = return (idDsWrapper, p)
533 tidy1 _ p@(BangPat (L _ (WildPat _))) = return (idDsWrapper, p)
534 tidy1 _ p@(BangPat (L _ (CoPat _ _ _))) = return (idDsWrapper, p)
535 tidy1 _ p@(BangPat (L _ (SigPatIn _ _))) = return (idDsWrapper, p)
536 tidy1 _ p@(BangPat (L _ (SigPatOut _ _))) = return (idDsWrapper, p)
537 tidy1 v (BangPat (L _ (AsPat (L _ var) pat)))
538 = do { (wrap, pat') <- tidy1 v (BangPat pat)
539 ; return (wrapBind var v . wrap, pat') }
540 tidy1 v (BangPat (L _ p)) = tidy1 v p
542 -- Everything else goes through unchanged...
544 tidy1 _ non_interesting_pat
545 = return (idDsWrapper, non_interesting_pat)
549 {\bf Previous @matchTwiddled@ stuff:}
551 Now we get to the only interesting part; note: there are choices for
552 translation [from Simon's notes]; translation~1:
559 s = case w of [s,t] -> s
560 t = case w of [s,t] -> t
564 Here \tr{w} is a fresh variable, and the \tr{w}-binding prevents multiple
565 evaluation of \tr{e}. An alternative translation (No.~2):
567 [ w = case e of [s,t] -> (s,t)
568 s = case w of (s,t) -> s
569 t = case w of (s,t) -> t
573 %************************************************************************
575 \subsubsection[improved-unmixing]{UNIMPLEMENTED idea for improved unmixing}
577 %************************************************************************
579 We might be able to optimise unmixing when confronted by
580 only-one-constructor-possible, of which tuples are the most notable
588 This definition would normally be unmixed into four equation blocks,
589 one per equation. But it could be unmixed into just one equation
590 block, because if the one equation matches (on the first column),
591 the others certainly will.
593 You have to be careful, though; the example
601 {\em must} be broken into two blocks at the line shown; otherwise, you
602 are forcing unnecessary evaluation. In any case, the top-left pattern
603 always gives the cue. You could then unmix blocks into groups of...
605 \item[all variables:]
607 \item[constructors or variables (mixed):]
608 Need to make sure the right names get bound for the variable patterns.
609 \item[literals or variables (mixed):]
610 Presumably just a variant on the constructor case (as it is now).
613 %************************************************************************
615 %* matchWrapper: a convenient way to call @match@ *
617 %************************************************************************
618 \subsection[matchWrapper]{@matchWrapper@: a convenient interface to @match@}
620 Calls to @match@ often involve similar (non-trivial) work; that work
621 is collected here, in @matchWrapper@. This function takes as
625 Typchecked @Matches@ (of a function definition, or a case or lambda
626 expression)---the main input;
628 An error message to be inserted into any (runtime) pattern-matching
632 As results, @matchWrapper@ produces:
635 A list of variables (@Locals@) that the caller must ``promise'' to
636 bind to appropriate values; and
638 a @CoreExpr@, the desugared output (main result).
641 The main actions of @matchWrapper@ include:
644 Flatten the @[TypecheckedMatch]@ into a suitable list of
647 Create as many new variables as there are patterns in a pattern-list
648 (in any one of the @EquationInfo@s).
650 Create a suitable ``if it fails'' expression---a call to @error@ using
651 the error-string input; the {\em type} of this fail value can be found
652 by examining one of the RHS expressions in one of the @EquationInfo@s.
654 Call @match@ with all of this information!
658 matchWrapper :: HsMatchContext Name -- For shadowing warning messages
659 -> MatchGroup Id -- Matches being desugared
660 -> DsM ([Id], CoreExpr) -- Results
663 There is one small problem with the Lambda Patterns, when somebody
664 writes something similar to:
668 he/she don't want a warning about incomplete patterns, that is done with
669 the flag @opt_WarnSimplePatterns@.
670 This problem also appears in the:
672 \item @do@ patterns, but if the @do@ can fail
673 it creates another equation if the match can fail
674 (see @DsExpr.doDo@ function)
675 \item @let@ patterns, are treated by @matchSimply@
676 List Comprension Patterns, are treated by @matchSimply@ also
679 We can't call @matchSimply@ with Lambda patterns,
680 due to the fact that lambda patterns can have more than
681 one pattern, and match simply only accepts one pattern.
686 matchWrapper ctxt (MatchGroup matches match_ty)
687 = ASSERT( notNull matches )
688 do { eqns_info <- mapM mk_eqn_info matches
689 ; new_vars <- selectMatchVars arg_pats
690 ; result_expr <- matchEquations ctxt new_vars eqns_info rhs_ty
691 ; return (new_vars, result_expr) }
693 arg_pats = map unLoc (hsLMatchPats (head matches))
694 n_pats = length arg_pats
695 (_, rhs_ty) = splitFunTysN n_pats match_ty
697 mk_eqn_info (L _ (Match pats _ grhss))
698 = do { let upats = map unLoc pats
699 ; match_result <- dsGRHSs ctxt upats grhss rhs_ty
700 ; return (EqnInfo { eqn_pats = upats, eqn_rhs = match_result}) }
703 matchEquations :: HsMatchContext Name
704 -> [Id] -> [EquationInfo] -> Type
706 matchEquations ctxt vars eqns_info rhs_ty
707 = do { locn <- getSrcSpanDs
708 ; let ds_ctxt = DsMatchContext ctxt locn
709 error_doc = matchContextErrString ctxt
711 ; match_result <- matchCheck ds_ctxt vars rhs_ty eqns_info
713 ; fail_expr <- mkErrorAppDs pAT_ERROR_ID rhs_ty error_doc
714 ; extractMatchResult match_result fail_expr }
717 %************************************************************************
719 \subsection[matchSimply]{@matchSimply@: match a single expression against a single pattern}
721 %************************************************************************
723 @mkSimpleMatch@ is a wrapper for @match@ which deals with the
724 situation where we want to match a single expression against a single
725 pattern. It returns an expression.
728 matchSimply :: CoreExpr -- Scrutinee
729 -> HsMatchContext Name -- Match kind
730 -> LPat Id -- Pattern it should match
731 -> CoreExpr -- Return this if it matches
732 -> CoreExpr -- Return this if it doesn't
734 -- Do not warn about incomplete patterns; see matchSinglePat comments
735 matchSimply scrut hs_ctx pat result_expr fail_expr = do
737 match_result = cantFailMatchResult result_expr
738 rhs_ty = exprType fail_expr
739 -- Use exprType of fail_expr, because won't refine in the case of failure!
740 match_result' <- matchSinglePat scrut hs_ctx pat rhs_ty match_result
741 extractMatchResult match_result' fail_expr
743 matchSinglePat :: CoreExpr -> HsMatchContext Name -> LPat Id
744 -> Type -> MatchResult -> DsM MatchResult
745 -- Do not warn about incomplete patterns
746 -- Used for things like [ e | pat <- stuff ], where
747 -- incomplete patterns are just fine
748 matchSinglePat (Var var) ctx (L _ pat) ty match_result
749 = do { locn <- getSrcSpanDs
750 ; matchCheck (DsMatchContext ctx locn)
752 [EqnInfo { eqn_pats = [pat], eqn_rhs = match_result }] }
754 matchSinglePat scrut hs_ctx pat ty match_result
755 = do { var <- selectSimpleMatchVarL pat
756 ; match_result' <- matchSinglePat (Var var) hs_ctx pat ty match_result
757 ; return (adjustMatchResult (bindNonRec var scrut) match_result') }
761 %************************************************************************
763 Pattern classification
765 %************************************************************************
769 = PgAny -- Immediate match: variables, wildcards,
771 | PgCon DataCon -- Constructor patterns (incl list, tuple)
772 | PgLit Literal -- Literal patterns
773 | PgN Literal -- Overloaded literals
774 | PgNpK Literal -- n+k patterns
775 | PgBang -- Bang patterns
776 | PgCo Type -- Coercion patterns; the type is the type
777 -- of the pattern *inside*
778 | PgView (LHsExpr Id) -- view pattern (e -> p):
779 -- the LHsExpr is the expression e
780 Type -- the Type is the type of p (equivalently, the result type of e)
782 groupEquations :: [EquationInfo] -> [[(PatGroup, EquationInfo)]]
783 -- If the result is of form [g1, g2, g3],
784 -- (a) all the (pg,eq) pairs in g1 have the same pg
785 -- (b) none of the gi are empty
786 -- The ordering of equations is unchanged
788 = runs same_gp [(patGroup (firstPat eqn), eqn) | eqn <- eqns]
790 same_gp :: (PatGroup,EquationInfo) -> (PatGroup,EquationInfo) -> Bool
791 (pg1,_) `same_gp` (pg2,_) = pg1 `sameGroup` pg2
793 subGroup :: Ord a => [(a, EquationInfo)] -> [[EquationInfo]]
794 -- Input is a particular group. The result sub-groups the
795 -- equations by with particular constructor, literal etc they match.
796 -- Each sub-list in the result has the same PatGroup
797 -- See Note [Take care with pattern order]
799 = map reverse $ Map.elems $ foldl accumulate Map.empty group
801 accumulate pg_map (pg, eqn)
802 = case Map.lookup pg pg_map of
803 Just eqns -> Map.insert pg (eqn:eqns) pg_map
804 Nothing -> Map.insert pg [eqn] pg_map
806 -- pg_map :: Map a [EquationInfo]
807 -- Equations seen so far in reverse order of appearance
810 Note [Take care with pattern order]
811 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
812 In the subGroup function we must be very careful about pattern re-ordering,
813 Consider the patterns [ (True, Nothing), (False, x), (True, y) ]
814 Then in bringing together the patterns for True, we must not
815 swap the Nothing and y!
819 sameGroup :: PatGroup -> PatGroup -> Bool
820 -- Same group means that a single case expression
821 -- or test will suffice to match both, *and* the order
822 -- of testing within the group is insignificant.
823 sameGroup PgAny PgAny = True
824 sameGroup PgBang PgBang = True
825 sameGroup (PgCon _) (PgCon _) = True -- One case expression
826 sameGroup (PgLit _) (PgLit _) = True -- One case expression
827 sameGroup (PgN l1) (PgN l2) = l1==l2 -- Order is significant
828 sameGroup (PgNpK l1) (PgNpK l2) = l1==l2 -- See Note [Grouping overloaded literal patterns]
829 sameGroup (PgCo t1) (PgCo t2) = t1 `eqType` t2
830 -- CoPats are in the same goup only if the type of the
831 -- enclosed pattern is the same. The patterns outside the CoPat
832 -- always have the same type, so this boils down to saying that
833 -- the two coercions are identical.
834 sameGroup (PgView e1 t1) (PgView e2 t2) = viewLExprEq (e1,t1) (e2,t2)
835 -- ViewPats are in the same gorup iff the expressions
836 -- are "equal"---conservatively, we use syntactic equality
837 sameGroup _ _ = False
839 -- An approximation of syntactic equality used for determining when view
840 -- exprs are in the same group.
841 -- This function can always safely return false;
842 -- but doing so will result in the application of the view function being repeated.
844 -- Currently: compare applications of literals and variables
845 -- and anything else that we can do without involving other
846 -- HsSyn types in the recursion
848 -- NB we can't assume that the two view expressions have the same type. Consider
849 -- f (e1 -> True) = ...
850 -- f (e2 -> "hi") = ...
851 viewLExprEq :: (LHsExpr Id,Type) -> (LHsExpr Id,Type) -> Bool
852 viewLExprEq (e1,_) (e2,_) = lexp e1 e2
854 lexp :: LHsExpr Id -> LHsExpr Id -> Bool
855 lexp e e' = exp (unLoc e) (unLoc e')
858 exp :: HsExpr Id -> HsExpr Id -> Bool
859 -- real comparison is on HsExpr's
861 exp (HsPar (L _ e)) e' = exp e e'
862 exp e (HsPar (L _ e')) = exp e e'
863 -- because the expressions do not necessarily have the same type,
864 -- we have to compare the wrappers
865 exp (HsWrap h e) (HsWrap h' e') = wrap h h' && exp e e'
866 exp (HsVar i) (HsVar i') = i == i'
867 -- the instance for IPName derives using the id, so this works if the
869 exp (HsIPVar i) (HsIPVar i') = i == i'
870 exp (HsOverLit l) (HsOverLit l') =
871 -- Overloaded lits are equal if they have the same type
872 -- and the data is the same.
873 -- this is coarser than comparing the SyntaxExpr's in l and l',
874 -- which resolve the overloading (e.g., fromInteger 1),
875 -- because these expressions get written as a bunch of different variables
876 -- (presumably to improve sharing)
877 eqType (overLitType l) (overLitType l') && l == l'
878 exp (HsApp e1 e2) (HsApp e1' e2') = lexp e1 e1' && lexp e2 e2'
879 -- the fixities have been straightened out by now, so it's safe
881 exp (OpApp l o _ ri) (OpApp l' o' _ ri') =
882 lexp l l' && lexp o o' && lexp ri ri'
883 exp (NegApp e n) (NegApp e' n') = lexp e e' && exp n n'
884 exp (SectionL e1 e2) (SectionL e1' e2') =
885 lexp e1 e1' && lexp e2 e2'
886 exp (SectionR e1 e2) (SectionR e1' e2') =
887 lexp e1 e1' && lexp e2 e2'
888 exp (ExplicitTuple es1 _) (ExplicitTuple es2 _) =
889 eq_list tup_arg es1 es2
890 exp (HsIf _ e e1 e2) (HsIf _ e' e1' e2') =
891 lexp e e' && lexp e1 e1' && lexp e2 e2'
893 -- Enhancement: could implement equality for more expressions
894 -- if it seems useful
895 -- But no need for HsLit, ExplicitList, ExplicitTuple,
896 -- because they cannot be functions
900 tup_arg (Present e1) (Present e2) = lexp e1 e2
901 tup_arg (Missing t1) (Missing t2) = eqType t1 t2
905 wrap :: HsWrapper -> HsWrapper -> Bool
906 -- Conservative, in that it demands that wrappers be
907 -- syntactically identical and doesn't look under binders
909 -- Coarser notions of equality are possible
910 -- (e.g., reassociating compositions,
911 -- equating different ways of writing a coercion)
912 wrap WpHole WpHole = True
913 wrap (WpCompose w1 w2) (WpCompose w1' w2') = wrap w1 w1' && wrap w2 w2'
914 wrap (WpCast c) (WpCast c') = coreEqCoercion c c'
915 wrap (WpEvApp et1) (WpEvApp et2) = ev_term et1 et2
916 wrap (WpTyApp t) (WpTyApp t') = eqType t t'
917 -- Enhancement: could implement equality for more wrappers
918 -- if it seems useful (lams and lets)
922 ev_term :: EvTerm -> EvTerm -> Bool
923 ev_term (EvId a) (EvId b) = a==b
924 ev_term (EvCoercion a) (EvCoercion b) = coreEqCoercion a b
928 eq_list :: (a->a->Bool) -> [a] -> [a] -> Bool
929 eq_list _ [] [] = True
930 eq_list _ [] (_:_) = False
931 eq_list _ (_:_) [] = False
932 eq_list eq (x:xs) (y:ys) = eq x y && eq_list eq xs ys
934 patGroup :: Pat Id -> PatGroup
935 patGroup (WildPat {}) = PgAny
936 patGroup (BangPat {}) = PgBang
937 patGroup (ConPatOut { pat_con = dc }) = PgCon (unLoc dc)
938 patGroup (LitPat lit) = PgLit (hsLitKey lit)
939 patGroup (NPat olit mb_neg _) = PgN (hsOverLitKey olit (isJust mb_neg))
940 patGroup (NPlusKPat _ olit _ _) = PgNpK (hsOverLitKey olit False)
941 patGroup (CoPat _ p _) = PgCo (hsPatType p) -- Type of innelexp pattern
942 patGroup (ViewPat expr p _) = PgView expr (hsPatType (unLoc p))
943 patGroup pat = pprPanic "patGroup" (ppr pat)
946 Note [Grouping overloaded literal patterns]
947 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
954 We can't group the first and third together, because the second may match
955 the same thing as the first. Same goes for *overloaded* literal patterns
959 If the first arg matches '1' but the second does not match 'True', we
960 cannot jump to the third equation! Because the same argument might
962 Hence we don't regard 1 and 2, or (n+1) and (n+2), as part of the same group.