2 % (c) The GRASP/AQUA Project, Glasgow University, 1997-1998
4 % Author: Juan J. Quintela <quintela@krilin.dc.fi.udc.es>
5 \section{Module @Check@ in @deSugar@}
10 module Check ( check , ExhaustivePat ) where
14 import TcHsSyn ( TypecheckedPat, hsPatType )
15 import TcType ( tcTyConAppTyCon )
16 import DsUtils ( EquationInfo(..), MatchResult(..), EqnSet,
17 CanItFail(..), tidyLitPat, tidyNPat,
20 import DataCon ( DataCon, dataConTyCon, dataConOrigArgTys, dataConFieldLabels )
21 import Name ( Name, mkInternalName, getOccName, isDataSymOcc, getName, mkVarOcc )
23 import PrelNames ( unboundKey )
24 import TyCon ( tyConDataCons, tupleTyConBoxity, isTupleTyCon )
25 import BasicTypes ( Boxity(..) )
26 import SrcLoc ( noSrcLoc )
28 import Util ( takeList, splitAtList, notNull )
32 #include "HsVersions.h"
35 This module performs checks about if one list of equations are:
40 To discover that we go through the list of equations in a tree-like fashion.
42 If you like theory, a similar algorithm is described in:
44 {\em Two Techniques for Compiling Lazy Pattern Matching},
46 INRIA Rocquencourt (RR-2385, 1994)
48 The algorithm is based on the first technique, but there are some differences:
50 \item We don't generate code
51 \item We have constructors and literals (not only literals as in the
53 \item We don't use directions, we must select the columns from
56 (By the way the second technique is really similar to the one used in
57 @Match.lhs@ to generate code)
59 This function takes the equations of a pattern and returns:
61 \item The patterns that are not recognized
62 \item The equations that are not overlapped
64 It simplify the patterns and then call @check'@ (the same semantics), and it
65 needs to reconstruct the patterns again ....
67 The problem appear with things like:
72 We want to put the two patterns with the same syntax, (prefix form) and
73 then all the constructors are equal:
75 f (: x (: y [])) = ....
78 (more about that in @simplify_eqns@)
80 We would prefer to have a @WarningPat@ of type @String@, but Strings and the
81 Pretty Printer are not friends.
83 We use @InPat@ in @WarningPat@ instead of @OutPat@
84 because we need to print the
85 warning messages in the same way they are introduced, i.e. if the user
90 He don't want a warning message written:
92 f (: x (: y [])) ........
94 Then we need to use InPats.
96 Juan Quintela 5 JUL 1998\\
97 User-friendliness and compiler writers are no friends.
101 type WarningPat = InPat Name
102 type ExhaustivePat = ([WarningPat], [(Name, [HsLit])])
105 check :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
106 check qs = (untidy_warns, incomplete)
108 (warns, incomplete) = check' (simplify_eqns qs)
109 untidy_warns = map untidy_exhaustive warns
111 untidy_exhaustive :: ExhaustivePat -> ExhaustivePat
112 untidy_exhaustive ([pat], messages) =
113 ([untidy_no_pars pat], map untidy_message messages)
114 untidy_exhaustive (pats, messages) =
115 (map untidy_pars pats, map untidy_message messages)
117 untidy_message :: (Name, [HsLit]) -> (Name, [HsLit])
118 untidy_message (string, lits) = (string, map untidy_lit lits)
121 The function @untidy@ does the reverse work of the @simplify_pat@ funcion.
127 untidy_no_pars :: WarningPat -> WarningPat
128 untidy_no_pars p = untidy False p
130 untidy_pars :: WarningPat -> WarningPat
131 untidy_pars p = untidy True p
133 untidy :: NeedPars -> WarningPat -> WarningPat
134 untidy _ p@(WildPat _) = p
135 untidy _ p@(VarPat name) = p
136 untidy _ (LitPat lit) = LitPat (untidy_lit lit)
137 untidy _ p@(ConPatIn name (PrefixCon [])) = p
138 untidy b (ConPatIn name ps) = pars b (ConPatIn name (untidy_con ps))
139 untidy _ (ListPat pats ty) = ListPat (map untidy_no_pars pats) ty
140 untidy _ (TuplePat pats boxed) = TuplePat (map untidy_no_pars pats) boxed
141 untidy _ (PArrPat _ _) = panic "Check.untidy: Shouldn't get a parallel array here!"
142 untidy _ (SigPatIn _ _) = panic "Check.untidy: SigPat"
144 untidy_con (PrefixCon pats) = PrefixCon (map untidy_pars pats)
145 untidy_con (InfixCon p1 p2) = InfixCon (untidy_pars p1) (untidy_pars p2)
146 untidy_con (RecCon bs) = RecCon [(f,untidy_pars p) | (f,p) <- bs]
148 pars :: NeedPars -> WarningPat -> WarningPat
149 pars True p = ParPat p
152 untidy_lit :: HsLit -> HsLit
153 untidy_lit (HsCharPrim c) = HsChar c
157 This equation is the same that check, the only difference is that the
158 boring work is done, that work needs to be done only once, this is
159 the reason top have two functions, check is the external interface,
160 @check'@ is called recursively.
162 There are several cases:
165 \item There are no equations: Everything is OK.
166 \item There are only one equation, that can fail, and all the patterns are
167 variables. Then that equation is used and the same equation is
169 \item All the patterns are variables, and the match can fail, there are
170 more equations then the results is the result of the rest of equations
171 and this equation is used also.
173 \item The general case, if all the patterns are variables (here the match
174 can't fail) then the result is that this equation is used and this
175 equation doesn't generate non-exhaustive cases.
177 \item In the general case, there can exist literals ,constructors or only
178 vars in the first column, we actuate in consequence.
185 check' :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
186 check' [] = ([([],[])],emptyUniqSet)
188 check' [EqnInfo n ctx ps (MatchResult CanFail _)]
189 | all_vars ps = ([(takeList ps (repeat new_wild_pat),[])], unitUniqSet n)
191 check' qs@((EqnInfo n ctx ps (MatchResult CanFail _)):rs)
192 | all_vars ps = (pats, addOneToUniqSet indexs n)
194 (pats,indexs) = check' rs
196 check' qs@((EqnInfo n ctx ps result):_)
197 | all_vars ps = ([], unitUniqSet n)
198 -- | nplusk = panic "Check.check': Work in progress: nplusk"
199 -- | npat = panic "Check.check': Work in progress: npat ?????"
200 | literals = split_by_literals qs
201 | constructors = split_by_constructor qs
202 | only_vars = first_column_only_vars qs
203 | otherwise = pprPanic "Check.check': Not implemented :-(" (ppr first_pats)
205 -- Note: RecPats will have been simplified to ConPats
207 first_pats = ASSERT2( okGroup qs, pprGroup qs ) map firstPat qs
208 constructors = any is_con first_pats
209 literals = any is_lit first_pats
210 only_vars = all is_var first_pats
211 -- npat = or (map is_npat qs)
212 -- nplusk = or (map is_nplusk qs)
215 Here begins the code to deal with literals, we need to split the matrix
216 in different matrix beginning by each literal and a last matrix with the
220 split_by_literals :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
221 split_by_literals qs = process_literals used_lits qs
223 used_lits = get_used_lits qs
226 @process_explicit_literals@ is a function that process each literal that appears
227 in the column of the matrix.
230 process_explicit_literals :: [HsLit] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
231 process_explicit_literals lits qs = (concat pats, unionManyUniqSets indexs)
233 pats_indexs = map (\x -> construct_literal_matrix x qs) lits
234 (pats,indexs) = unzip pats_indexs
239 @process_literals@ calls @process_explicit_literals@ to deal with the literals
240 that appears in the matrix and deal also with the rest of the cases. It
241 must be one Variable to be complete.
245 process_literals :: [HsLit] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
246 process_literals used_lits qs
247 | null default_eqns = ([make_row_vars used_lits (head qs)]++pats,indexs)
248 | otherwise = (pats_default,indexs_default)
250 (pats,indexs) = process_explicit_literals used_lits qs
251 default_eqns = ASSERT2( okGroup qs, pprGroup qs )
252 map remove_var (filter (is_var . firstPat) qs)
253 (pats',indexs') = check' default_eqns
254 pats_default = [(new_wild_pat:ps,constraints) | (ps,constraints) <- (pats')] ++ pats
255 indexs_default = unionUniqSets indexs' indexs
258 Here we have selected the literal and we will select all the equations that
259 begins for that literal and create a new matrix.
262 construct_literal_matrix :: HsLit -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
263 construct_literal_matrix lit qs =
264 (map (\ (xs,ys) -> (new_lit:xs,ys)) pats,indexs)
266 (pats,indexs) = (check' (remove_first_column_lit lit qs))
269 remove_first_column_lit :: HsLit
272 remove_first_column_lit lit qs
273 = ASSERT2( okGroup qs, pprGroup qs )
274 map shift_pat (filter (is_var_lit lit . firstPat) qs)
276 shift_pat (EqnInfo n ctx [] result) = panic "Check.shift_var: no patterns"
277 shift_pat (EqnInfo n ctx (_:ps) result) = EqnInfo n ctx ps result
281 This function splits the equations @qs@ in groups that deal with the
286 split_by_constructor :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
288 split_by_constructor qs
289 | notNull unused_cons = need_default_case used_cons unused_cons qs
290 | otherwise = no_need_default_case used_cons qs
292 used_cons = get_used_cons qs
293 unused_cons = get_unused_cons used_cons
297 The first column of the patterns matrix only have vars, then there is
301 first_column_only_vars :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
302 first_column_only_vars qs = (map (\ (xs,ys) -> (new_wild_pat:xs,ys)) pats,indexs)
304 (pats,indexs) = check' (map remove_var qs)
308 This equation takes a matrix of patterns and split the equations by
309 constructor, using all the constructors that appears in the first column
310 of the pattern matching.
312 We can need a default clause or not ...., it depends if we used all the
313 constructors or not explicitly. The reasoning is similar to @process_literals@,
314 the difference is that here the default case is not always needed.
317 no_need_default_case :: [TypecheckedPat] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
318 no_need_default_case cons qs = (concat pats, unionManyUniqSets indexs)
320 pats_indexs = map (\x -> construct_matrix x qs) cons
321 (pats,indexs) = unzip pats_indexs
323 need_default_case :: [TypecheckedPat] -> [DataCon] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
324 need_default_case used_cons unused_cons qs
325 | null default_eqns = (pats_default_no_eqns,indexs)
326 | otherwise = (pats_default,indexs_default)
328 (pats,indexs) = no_need_default_case used_cons qs
329 default_eqns = ASSERT2( okGroup qs, pprGroup qs ) map remove_var (filter (is_var . firstPat) qs)
330 (pats',indexs') = check' default_eqns
331 pats_default = [(make_whole_con c:ps,constraints) |
332 c <- unused_cons, (ps,constraints) <- pats'] ++ pats
333 new_wilds = make_row_vars_for_constructor (head qs)
334 pats_default_no_eqns = [(make_whole_con c:new_wilds,[]) | c <- unused_cons] ++ pats
335 indexs_default = unionUniqSets indexs' indexs
337 construct_matrix :: TypecheckedPat -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
338 construct_matrix con qs =
339 (map (make_con con) pats,indexs)
341 (pats,indexs) = (check' (remove_first_column con qs))
344 Here remove first column is more difficult that with literals due to the fact
345 that constructors can have arguments.
347 For instance, the matrix
359 remove_first_column :: TypecheckedPat -- Constructor
362 remove_first_column (ConPatOut con (PrefixCon con_pats) _ _ _) qs
363 = ASSERT2( okGroup qs, pprGroup qs )
364 map shift_var (filter (is_var_con con . firstPat) qs)
366 new_wilds = [WildPat (hsPatType arg_pat) | arg_pat <- con_pats]
367 shift_var (EqnInfo n ctx (ConPatOut _ (PrefixCon ps') _ _ _:ps) result) =
368 EqnInfo n ctx (ps'++ps) result
369 shift_var (EqnInfo n ctx (WildPat _ :ps) result) =
370 EqnInfo n ctx (new_wilds ++ ps) result
371 shift_var _ = panic "Check.Shift_var:No done"
373 make_row_vars :: [HsLit] -> EquationInfo -> ExhaustivePat
374 make_row_vars used_lits (EqnInfo _ _ pats _ ) =
375 (VarPat new_var:takeList (tail pats) (repeat new_wild_pat),[(new_var,used_lits)])
376 where new_var = hash_x
378 hash_x = mkInternalName unboundKey {- doesn't matter much -}
379 (mkVarOcc FSLIT("#x"))
382 make_row_vars_for_constructor :: EquationInfo -> [WarningPat]
383 make_row_vars_for_constructor (EqnInfo _ _ pats _ ) = takeList (tail pats) (repeat new_wild_pat)
385 compare_cons :: TypecheckedPat -> TypecheckedPat -> Bool
386 compare_cons (ConPatOut id1 _ _ _ _) (ConPatOut id2 _ _ _ _) = id1 == id2
388 remove_dups :: [TypecheckedPat] -> [TypecheckedPat]
390 remove_dups (x:xs) | or (map (\y -> compare_cons x y) xs) = remove_dups xs
391 | otherwise = x : remove_dups xs
393 get_used_cons :: [EquationInfo] -> [TypecheckedPat]
394 get_used_cons qs = remove_dups [con | (EqnInfo _ _ (con@(ConPatOut _ _ _ _ _):_) _) <- qs ]
396 remove_dups' :: [HsLit] -> [HsLit]
398 remove_dups' (x:xs) | x `elem` xs = remove_dups' xs
399 | otherwise = x : remove_dups' xs
402 get_used_lits :: [EquationInfo] -> [HsLit]
403 get_used_lits qs = remove_dups' all_literals
405 all_literals = get_used_lits' qs
407 get_used_lits' :: [EquationInfo] -> [HsLit]
408 get_used_lits' [] = []
409 get_used_lits' ((EqnInfo _ _ ((LitPat lit):_) _):qs) =
410 lit : get_used_lits qs
411 get_used_lits' ((EqnInfo _ _ ((NPatOut lit _ _):_) _):qs) =
412 lit : get_used_lits qs
413 get_used_lits' (q:qs) =
416 get_unused_cons :: [TypecheckedPat] -> [DataCon]
417 get_unused_cons used_cons = unused_cons
419 (ConPatOut _ _ ty _ _) = head used_cons
420 ty_con = tcTyConAppTyCon ty -- Newtype observable
421 all_cons = tyConDataCons ty_con
422 used_cons_as_id = map (\ (ConPatOut d _ _ _ _) -> d) used_cons
423 unused_cons = uniqSetToList
424 (mkUniqSet all_cons `minusUniqSet` mkUniqSet used_cons_as_id)
426 all_vars :: [TypecheckedPat] -> Bool
428 all_vars (WildPat _:ps) = all_vars ps
431 remove_var :: EquationInfo -> EquationInfo
432 remove_var (EqnInfo n ctx (WildPat _:ps) result) = EqnInfo n ctx ps result
434 panic "Check.remove_var: equation does not begin with a variable"
436 -----------------------
437 eqnPats :: EquationInfo -> [TypecheckedPat]
438 eqnPats (EqnInfo _ _ ps _) = ps
440 firstPat :: EquationInfo -> TypecheckedPat
441 firstPat eqn_info = head (eqnPats eqn_info)
443 okGroup :: [EquationInfo] -> Bool
444 -- True if all equations have at least one pattern, and
445 -- all have the same number of patterns
447 okGroup (e:es) = n_pats > 0 && and [length (eqnPats e) == n_pats | e <- es]
449 n_pats = length (eqnPats e)
452 pprGroup es = vcat (map pprEqnInfo es)
453 pprEqnInfo e = ppr (eqnPats e)
455 is_con :: TypecheckedPat -> Bool
456 is_con (ConPatOut _ _ _ _ _) = True
459 is_lit :: TypecheckedPat -> Bool
460 is_lit (LitPat _) = True
461 is_lit (NPatOut _ _ _) = True
464 is_npat :: TypecheckedPat -> Bool
465 is_npat (NPatOut _ _ _) = True
468 is_nplusk :: TypecheckedPat -> Bool
469 is_nplusk (NPlusKPatOut _ _ _ _) = True
472 is_var :: TypecheckedPat -> Bool
473 is_var (WildPat _) = True
476 is_var_con :: DataCon -> TypecheckedPat -> Bool
477 is_var_con con (WildPat _) = True
478 is_var_con con (ConPatOut id _ _ _ _) | id == con = True
479 is_var_con con _ = False
481 is_var_lit :: HsLit -> TypecheckedPat -> Bool
482 is_var_lit lit (WildPat _) = True
483 is_var_lit lit (LitPat lit') | lit == lit' = True
484 is_var_lit lit (NPatOut lit' _ _) | lit == lit' = True
485 is_var_lit lit _ = False
488 The difference beteewn @make_con@ and @make_whole_con@ is that
489 @make_wole_con@ creates a new constructor with all their arguments, and
490 @make_con@ takes a list of argumntes, creates the contructor getting their
491 arguments from the list. See where \fbox{\ ???\ } are used for details.
493 We need to reconstruct the patterns (make the constructors infix and
494 similar) at the same time that we create the constructors.
496 You can tell tuple constructors using
500 You can see if one constructor is infix with this clearer code :-))))))))))
502 Lex.isLexConSym (Name.occNameString (Name.getOccName con))
505 Rather clumsy but it works. (Simon Peyton Jones)
508 We don't mind the @nilDataCon@ because it doesn't change the way to
509 print the messsage, we are searching only for things like: @[1,2,3]@,
512 In @reconstruct_pat@ we want to ``undo'' the work
513 that we have done in @simplify_pat@.
516 @((,) x y)@ & returns to be & @(x, y)@
517 \\ @((:) x xs)@ & returns to be & @(x:xs)@
518 \\ @(x:(...:[])@ & returns to be & @[x,...]@
521 The difficult case is the third one becouse we need to follow all the
522 contructors until the @[]@ to know that we need to use the second case,
523 not the second. \fbox{\ ???\ }
526 isInfixCon con = isDataSymOcc (getOccName con)
528 is_nil (ConPatIn con (PrefixCon [])) = con == getName nilDataCon
531 is_list (ListPat _ _) = True
534 return_list id q = id == consDataCon && (is_nil q || is_list q)
536 make_list p q | is_nil q = ListPat [p] placeHolderType
537 make_list p (ListPat ps ty) = ListPat (p:ps) ty
538 make_list _ _ = panic "Check.make_list: Invalid argument"
540 make_con :: TypecheckedPat -> ExhaustivePat -> ExhaustivePat
541 make_con (ConPatOut id _ _ _ _) (p:q:ps, constraints)
542 | return_list id q = (make_list p q : ps, constraints)
543 | isInfixCon id = (ConPatIn (getName id) (InfixCon p q) : ps, constraints)
545 make_con (ConPatOut id (PrefixCon pats) _ _ _) (ps, constraints)
546 | isTupleTyCon tc = (TuplePat pats_con (tupleTyConBoxity tc) : rest_pats, constraints)
547 | isPArrFakeCon id = (PArrPat pats_con placeHolderType : rest_pats, constraints)
548 | otherwise = (ConPatIn name (PrefixCon pats_con) : rest_pats, constraints)
551 (pats_con, rest_pats) = splitAtList pats ps
554 -- reconstruct parallel array pattern
556 -- * don't check for the type only; we need to make sure that we are really
557 -- dealing with one of the fake constructors and not with the real
560 make_whole_con :: DataCon -> WarningPat
561 make_whole_con con | isInfixCon con = ConPatIn name (InfixCon new_wild_pat new_wild_pat)
562 | otherwise = ConPatIn name (PrefixCon pats)
565 pats = [new_wild_pat | t <- dataConOrigArgTys con]
567 new_wild_pat :: WarningPat
568 new_wild_pat = WildPat placeHolderType
571 This equation makes the same thing as @tidy@ in @Match.lhs@, the
572 difference is that here we can do all the tidy in one place and in the
573 @Match@ tidy it must be done one column each time due to bookkeeping
578 simplify_eqns :: [EquationInfo] -> [EquationInfo]
579 simplify_eqns [] = []
580 simplify_eqns ((EqnInfo n ctx pats result):qs) =
581 (EqnInfo n ctx pats' result) : simplify_eqns qs
583 pats' = map simplify_pat pats
585 simplify_pat :: TypecheckedPat -> TypecheckedPat
587 simplify_pat pat@(WildPat gt) = pat
588 simplify_pat (VarPat id) = WildPat (idType id)
590 simplify_pat (ParPat p) = simplify_pat p
591 simplify_pat (LazyPat p) = simplify_pat p
592 simplify_pat (AsPat id p) = simplify_pat p
593 simplify_pat (SigPatOut p ty fn) = simplify_pat p -- I'm not sure this is right
595 simplify_pat (ConPatOut id ps ty tvs dicts) = ConPatOut id (simplify_con id ps) ty tvs dicts
597 simplify_pat (ListPat ps ty) = foldr (\ x y -> mkPrefixConPat consDataCon [x,y] list_ty)
599 (map simplify_pat ps)
600 where list_ty = mkListTy ty
602 -- introduce fake parallel array constructors to be able to handle parallel
603 -- arrays with the existing machinery for constructor pattern
605 simplify_pat (PArrPat ps ty)
606 = ConPatOut (parrFakeCon arity)
607 (PrefixCon (map simplify_pat ps))
612 simplify_pat (TuplePat ps boxity)
613 = ConPatOut (tupleCon boxity arity)
614 (PrefixCon (map simplify_pat ps))
615 (mkTupleTy boxity arity (map hsPatType ps)) [] []
619 simplify_pat pat@(LitPat lit) = tidyLitPat lit pat
621 -- unpack string patterns fully, so we can see when they overlap with
622 -- each other, or even explicit lists of Chars.
623 simplify_pat pat@(NPatOut (HsString s) _ _) =
624 foldr (\c pat -> ConPatOut consDataCon (PrefixCon [mk_char_lit c,pat]) stringTy [] [])
625 (ConPatOut nilDataCon (PrefixCon []) stringTy [] []) (unpackIntFS s)
627 mk_char_lit c = ConPatOut charDataCon (PrefixCon [LitPat (HsCharPrim c)])
630 simplify_pat pat@(NPatOut lit lit_ty hsexpr) = tidyNPat lit lit_ty pat
632 simplify_pat (NPlusKPatOut id hslit hsexpr1 hsexpr2)
633 = WildPat (idType id)
635 simplify_pat (DictPat dicts methods)
636 = case num_of_d_and_ms of
637 0 -> simplify_pat (TuplePat [] Boxed)
638 1 -> simplify_pat (head dict_and_method_pats)
639 _ -> simplify_pat (TuplePat dict_and_method_pats Boxed)
641 num_of_d_and_ms = length dicts + length methods
642 dict_and_method_pats = map VarPat (dicts ++ methods)
645 simplify_con con (PrefixCon ps) = PrefixCon (map simplify_pat ps)
646 simplify_con con (InfixCon p1 p2) = PrefixCon [simplify_pat p1, simplify_pat p2]
647 simplify_con con (RecCon fs)
648 | null fs = PrefixCon [wild_pat | t <- dataConOrigArgTys con]
649 -- Special case for null patterns; maybe not a record at all
650 | otherwise = PrefixCon (map (simplify_pat.snd) all_pats)
652 -- pad out all the missing fields with WildPats.
653 field_pats = map (\ f -> (getName f, wild_pat))
654 (dataConFieldLabels con)
655 all_pats = foldr (\ (id,p) acc -> insertNm (getName id) p acc)
658 insertNm nm p [] = [(nm,p)]
659 insertNm nm p (x@(n,_):xs)
660 | nm == n = (nm,p):xs
661 | otherwise = x : insertNm nm p xs
663 wild_pat = WildPat (panic "Check.simplify_con")