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 )
15 import DsHsSyn ( outPatType )
18 import DsUtils ( EquationInfo(..),
25 import DataCon ( DataCon, isTupleCon, isUnboxedTupleCon, dataConArgTys,
26 dataConSourceArity, dataConFieldLabels )
27 import Name ( Name, mkLocalName, getOccName, isDataSymOcc, getName, mkSrcVarOcc )
28 import Type ( Type, splitAlgTyConApp, mkTyVarTys,
29 isUnboxedType, splitTyConApp_maybe
31 import TysPrim ( intPrimTy,
38 import TysWiredIn ( nilDataCon, consDataCon,
40 mkUnboxedTupleTy, unboxedTupleCon,
44 floatTy, floatDataCon,
45 doubleTy, doubleDataCon,
50 import Unique ( unboundKey )
51 import TyCon ( tyConDataCons )
52 import SrcLoc ( noSrcLoc )
56 #include "HsVersions.h"
59 This module performs checks about if one list of equations are:
64 To discover that we go through the list of equations in a tree-like fashion.
66 If you like theory, a similar algorithm is described in:
68 {\em Two Techniques for Compiling Lazy Pattern Matching},
70 INRIA Rocquencourt (RR-2385, 1994)
72 The algorithm is based on the first technique, but there are some differences:
74 \item We don't generate code
75 \item We have constructors and literals (not only literals as in the
77 \item We don't use directions, we must select the columns from
80 (By the way the second technique is really similar to the one used in
81 @Match.lhs@ to generate code)
83 This function takes the equations of a pattern and returns:
85 \item The patterns that are not recognized
86 \item The equations that are not overlapped
88 It simplify the patterns and then call @check'@ (the same semantics), and it
89 needs to reconstruct the patterns again ....
91 The problem appear with things like:
96 We want to put the two patterns with the same syntax, (prefix form) and
97 then all the constructors are equal:
99 f (: x (: y [])) = ....
102 (more about that in @simplify_eqns@)
104 We would prefer to have a @WarningPat@ of type @String@, but Strings and the
105 Pretty Printer are not friends.
107 We use @InPat@ in @WarningPat@ instead of @OutPat@
108 because we need to print the
109 warning messages in the same way they are introduced, i.e. if the user
114 He don't want a warning message written:
116 f (: x (: y [])) ........
118 Then we need to use InPats.
120 Juan Quintela 5 JUL 1998\\
121 User-friendliness and compiler writers are no friends.
125 type WarningPat = InPat Name
126 type ExhaustivePat = ([WarningPat], [(Name, [HsLit])])
129 check :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
130 check qs = (untidy_warns, incomplete)
132 (warns, incomplete) = check' (simplify_eqns qs)
133 untidy_warns = map untidy_exhaustive warns
135 untidy_exhaustive :: ExhaustivePat -> ExhaustivePat
136 untidy_exhaustive ([pat], messages) =
137 ([untidy_no_pars pat], map untidy_message messages)
138 untidy_exhaustive (pats, messages) =
139 (map untidy_pars pats, map untidy_message messages)
141 untidy_message :: (Name, [HsLit]) -> (Name, [HsLit])
142 untidy_message (string, lits) = (string, map untidy_lit lits)
145 The function @untidy@ does the reverse work of the @simplify_pat@ funcion.
151 untidy_no_pars :: WarningPat -> WarningPat
152 untidy_no_pars p = untidy False p
154 untidy_pars :: WarningPat -> WarningPat
155 untidy_pars p = untidy True p
157 untidy :: NeedPars -> WarningPat -> WarningPat
158 untidy _ p@WildPatIn = p
159 untidy _ p@(VarPatIn name) = p
160 untidy _ (LitPatIn lit) = LitPatIn (untidy_lit lit)
161 untidy _ p@(ConPatIn name []) = p
162 untidy b (ConPatIn name pats) =
163 pars b (ConPatIn name (map untidy_pars pats))
164 untidy b (ConOpPatIn pat1 name fixity pat2) =
165 pars b (ConOpPatIn (untidy_pars pat1) name fixity (untidy_pars pat2))
166 untidy _ (ListPatIn pats) = ListPatIn (map untidy_no_pars pats)
167 untidy _ (TuplePatIn pats boxed) = TuplePatIn (map untidy_no_pars pats) boxed
169 untidy _ (SigPatIn pat ty) = panic "Check.untidy: SigPatIn"
170 untidy _ (LazyPatIn pat) = panic "Check.untidy: LazyPatIn"
171 untidy _ (AsPatIn name pat) = panic "Check.untidy: AsPatIn"
172 untidy _ (NPlusKPatIn name lit) = panic "Check.untidy: NPlusKPatIn"
173 untidy _ (NegPatIn ipat) = panic "Check.untidy: NegPatIn"
174 untidy _ (ParPatIn pat) = panic "Check.untidy: ParPatIn"
175 untidy _ (RecPatIn name fields) = panic "Check.untidy: RecPatIn"
177 pars :: NeedPars -> WarningPat -> WarningPat
178 pars True p = ParPatIn p
181 untidy_lit :: HsLit -> HsLit
182 untidy_lit (HsCharPrim c) = HsChar c
183 --untidy_lit (HsStringPrim s) = HsString s
187 This equation is the same that check, the only difference is that the
188 boring work is done, that work needs to be done only once, this is
189 the reason top have two functions, check is the external interface,
190 @check'@ is called recursively.
192 There are several cases:
195 \item There are no equations: Everything is OK.
196 \item There are only one equation, that can fail, and all the patterns are
197 variables. Then that equation is used and the same equation is
199 \item All the patterns are variables, and the match can fail, there are
200 more equations then the results is the result of the rest of equations
201 and this equation is used also.
203 \item The general case, if all the patterns are variables (here the match
204 can't fail) then the result is that this equation is used and this
205 equation doesn't generate non-exhaustive cases.
207 \item In the general case, there can exist literals ,constructors or only
208 vars in the first column, we actuate in consequence.
215 check' :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
216 check' [] = ([([],[])],emptyUniqSet)
218 check' [EqnInfo n ctx ps (MatchResult CanFail _)]
219 | all_vars ps = ([(take (length ps) (repeat new_wild_pat),[])], unitUniqSet n)
221 check' qs@((EqnInfo n ctx ps (MatchResult CanFail _)):rs)
222 | all_vars ps = (pats, addOneToUniqSet indexs n)
224 (pats,indexs) = check' rs
226 check' qs@((EqnInfo n ctx ps result):_)
227 | all_vars ps = ([], unitUniqSet n)
228 -- | nplusk = panic "Check.check': Work in progress: nplusk"
229 -- | npat = panic "Check.check': Work in progress: npat ?????"
230 | literals = split_by_literals qs
231 | constructors = split_by_constructor qs
232 | only_vars = first_column_only_vars qs
233 | otherwise = panic "Check.check': Not implemented :-("
235 -- Note: RecPats will have been simplified to ConPats
237 constructors = or (map is_con qs)
238 literals = or (map is_lit qs)
239 only_vars = and (map is_var qs)
240 -- npat = or (map is_npat qs)
241 -- nplusk = or (map is_nplusk qs)
244 Here begins the code to deal with literals, we need to split the matrix
245 in different matrix beginning by each literal and a last matrix with the
249 split_by_literals :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
250 split_by_literals qs = process_literals used_lits qs
252 used_lits = get_used_lits qs
255 @process_explicit_literals@ is a function that process each literal that appears
256 in the column of the matrix.
259 process_explicit_literals :: [HsLit] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
260 process_explicit_literals lits qs = (concat pats, unionManyUniqSets indexs)
262 pats_indexs = map (\x -> construct_literal_matrix x qs) lits
263 (pats,indexs) = unzip pats_indexs
268 @process_literals@ calls @process_explicit_literals@ to deal with the literals
269 that appears in the matrix and deal also with the rest of the cases. It
270 must be one Variable to be complete.
274 process_literals :: [HsLit] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
275 process_literals used_lits qs
276 | length default_eqns == 0 = ([make_row_vars used_lits (head qs)]++pats,indexs)
277 | otherwise = (pats_default,indexs_default)
279 (pats,indexs) = process_explicit_literals used_lits qs
280 default_eqns = (map remove_var (filter is_var qs))
281 (pats',indexs') = check' default_eqns
282 pats_default = [(new_wild_pat:ps,constraints) | (ps,constraints) <- (pats')] ++ pats
283 indexs_default = unionUniqSets indexs' indexs
286 Here we have selected the literal and we will select all the equations that
287 begins for that literal and create a new matrix.
290 construct_literal_matrix :: HsLit -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
291 construct_literal_matrix lit qs =
292 (map (\ (xs,ys) -> (new_lit:xs,ys)) pats,indexs)
294 (pats,indexs) = (check' (remove_first_column_lit lit qs))
295 new_lit = LitPatIn lit
297 remove_first_column_lit :: HsLit
300 remove_first_column_lit lit qs =
301 map shift_pat (filter (is_var_lit lit) qs)
303 shift_pat (EqnInfo n ctx [] result) = panic "Check.shift_var: no patterns"
304 shift_pat (EqnInfo n ctx (_:ps) result) = EqnInfo n ctx ps result
308 This function splits the equations @qs@ in groups that deal with the
313 split_by_constructor :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
315 split_by_constructor qs | length unused_cons /= 0 = need_default_case used_cons unused_cons qs
316 | otherwise = no_need_default_case used_cons qs
318 used_cons = get_used_cons qs
319 unused_cons = get_unused_cons used_cons
323 The first column of the patterns matrix only have vars, then there is
327 first_column_only_vars :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
328 first_column_only_vars qs = (map (\ (xs,ys) -> (new_wild_pat:xs,ys)) pats,indexs)
330 (pats,indexs) = check' (map remove_var qs)
334 This equation takes a matrix of patterns and split the equations by
335 constructor, using all the constructors that appears in the first column
336 of the pattern matching.
338 We can need a default clause or not ...., it depends if we used all the
339 constructors or not explicitly. The reasoning is similar to @process_literals@,
340 the difference is that here the default case is not always needed.
343 no_need_default_case :: [TypecheckedPat] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
344 no_need_default_case cons qs = (concat pats, unionManyUniqSets indexs)
346 pats_indexs = map (\x -> construct_matrix x qs) cons
347 (pats,indexs) = unzip pats_indexs
349 need_default_case :: [TypecheckedPat] -> [DataCon] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
350 need_default_case used_cons unused_cons qs
351 | length default_eqns == 0 = (pats_default_no_eqns,indexs)
352 | otherwise = (pats_default,indexs_default)
354 (pats,indexs) = no_need_default_case used_cons qs
355 default_eqns = (map remove_var (filter is_var qs))
356 (pats',indexs') = check' default_eqns
357 pats_default = [(make_whole_con c:ps,constraints) |
358 c <- unused_cons, (ps,constraints) <- pats'] ++ pats
359 new_wilds = make_row_vars_for_constructor (head qs)
360 pats_default_no_eqns = [(make_whole_con c:new_wilds,[]) | c <- unused_cons] ++ pats
361 indexs_default = unionUniqSets indexs' indexs
363 construct_matrix :: TypecheckedPat -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
364 construct_matrix con qs =
365 (map (make_con con) pats,indexs)
367 (pats,indexs) = (check' (remove_first_column con qs))
370 Here remove first column is more difficult that with literals due to the fact
371 that constructors can have arguments.
373 For instance, the matrix
385 remove_first_column :: TypecheckedPat -- Constructor
388 remove_first_column (ConPat con _ _ _ con_pats) qs =
389 map shift_var (filter (is_var_con con) qs)
391 new_wilds = [WildPat (outPatType arg_pat) | arg_pat <- con_pats]
392 shift_var (EqnInfo n ctx (ConPat _ _ _ _ ps':ps) result) =
393 EqnInfo n ctx (ps'++ps) result
394 shift_var (EqnInfo n ctx (WildPat _ :ps) result) =
395 EqnInfo n ctx (new_wilds ++ ps) result
396 shift_var _ = panic "Check.Shift_var:No done"
398 make_row_vars :: [HsLit] -> EquationInfo -> ExhaustivePat
399 make_row_vars used_lits (EqnInfo _ _ pats _ ) =
400 (VarPatIn new_var:take (length (tail pats)) (repeat new_wild_pat),[(new_var,used_lits)])
401 where new_var = hash_x
403 hash_x = mkLocalName unboundKey {- doesn't matter much -}
404 (mkSrcVarOcc SLIT("#x"))
407 make_row_vars_for_constructor :: EquationInfo -> [WarningPat]
408 make_row_vars_for_constructor (EqnInfo _ _ pats _ ) = take (length (tail pats)) (repeat new_wild_pat)
410 compare_cons :: TypecheckedPat -> TypecheckedPat -> Bool
411 compare_cons (ConPat id1 _ _ _ _) (ConPat id2 _ _ _ _) = id1 == id2
413 remove_dups :: [TypecheckedPat] -> [TypecheckedPat]
415 remove_dups (x:xs) | or (map (\y -> compare_cons x y) xs) = remove_dups xs
416 | otherwise = x : remove_dups xs
418 get_used_cons :: [EquationInfo] -> [TypecheckedPat]
419 get_used_cons qs = remove_dups [con | (EqnInfo _ _ (con@(ConPat _ _ _ _ _):_) _) <- qs ]
421 remove_dups' :: [HsLit] -> [HsLit]
423 remove_dups' (x:xs) | x `elem` xs = remove_dups' xs
424 | otherwise = x : remove_dups' xs
427 get_used_lits :: [EquationInfo] -> [HsLit]
428 get_used_lits qs = remove_dups' all_literals
430 all_literals = get_used_lits' qs
432 get_used_lits' :: [EquationInfo] -> [HsLit]
433 get_used_lits' [] = []
434 get_used_lits' ((EqnInfo _ _ ((LitPat lit _):_) _):qs) =
435 lit : get_used_lits qs
436 get_used_lits' ((EqnInfo _ _ ((NPat lit _ _):_) _):qs) =
437 lit : get_used_lits qs
438 get_used_lits' (q:qs) =
441 get_unused_cons :: [TypecheckedPat] -> [DataCon]
442 get_unused_cons used_cons = unused_cons
444 (ConPat _ ty _ _ _) = head used_cons
445 Just (ty_con,_) = splitTyConApp_maybe ty
446 all_cons = tyConDataCons ty_con
447 used_cons_as_id = map (\ (ConPat d _ _ _ _) -> d) used_cons
448 unused_cons = uniqSetToList
449 (mkUniqSet all_cons `minusUniqSet` mkUniqSet used_cons_as_id)
452 all_vars :: [TypecheckedPat] -> Bool
454 all_vars (WildPat _:ps) = all_vars ps
457 remove_var :: EquationInfo -> EquationInfo
458 remove_var (EqnInfo n ctx (WildPat _:ps) result) = EqnInfo n ctx ps result
460 panic "Check.remove_var: equation does not begin with a variable"
462 is_con :: EquationInfo -> Bool
463 is_con (EqnInfo _ _ ((ConPat _ _ _ _ _):_) _) = True
466 is_lit :: EquationInfo -> Bool
467 is_lit (EqnInfo _ _ ((LitPat _ _):_) _) = True
468 is_lit (EqnInfo _ _ ((NPat _ _ _):_) _) = True
471 is_npat :: EquationInfo -> Bool
472 is_npat (EqnInfo _ _ ((NPat _ _ _):_) _) = True
475 is_nplusk :: EquationInfo -> Bool
476 is_nplusk (EqnInfo _ _ ((NPlusKPat _ _ _ _ _):_) _) = True
479 is_var :: EquationInfo -> Bool
480 is_var (EqnInfo _ _ ((WildPat _):_) _) = True
483 is_var_con :: DataCon -> EquationInfo -> Bool
484 is_var_con con (EqnInfo _ _ ((WildPat _):_) _) = True
485 is_var_con con (EqnInfo _ _ ((ConPat id _ _ _ _):_) _) | id == con = True
486 is_var_con con _ = False
488 is_var_lit :: HsLit -> EquationInfo -> Bool
489 is_var_lit lit (EqnInfo _ _ ((WildPat _):_) _) = True
490 is_var_lit lit (EqnInfo _ _ ((LitPat lit' _):_) _) | lit == lit' = True
491 is_var_lit lit (EqnInfo _ _ ((NPat lit' _ _):_) _) | lit == lit' = True
492 is_var_lit lit _ = False
495 The difference beteewn @make_con@ and @make_whole_con@ is that
496 @make_wole_con@ creates a new constructor with all their arguments, and
497 @make_con@ takes a list of argumntes, creates the contructor getting their
498 arguments from the list. See where \fbox{\ ???\ } are used for details.
500 We need to reconstruct the patterns (make the constructors infix and
501 similar) at the same time that we create the constructors.
503 You can tell tuple constructors using
507 You can see if one constructor is infix with this clearer code :-))))))))))
509 Lex.isLexConSym (Name.occNameString (Name.getOccName con))
512 Rather clumsy but it works. (Simon Peyton Jones)
515 We don't mind the @nilDataCon@ because it doesn't change the way to
516 print the messsage, we are searching only for things like: @[1,2,3]@,
519 In @reconstruct_pat@ we want to ``undo'' the work
520 that we have done in @simplify_pat@.
523 @((,) x y)@ & returns to be & @(x, y)@
524 \\ @((:) x xs)@ & returns to be & @(x:xs)@
525 \\ @(x:(...:[])@ & returns to be & @[x,...]@
528 The difficult case is the third one becouse we need to follow all the
529 contructors until the @[]@ to know that we need to use the second case,
530 not the second. \fbox{\ ???\ }
533 isInfixCon con = isDataSymOcc (getOccName con)
535 is_nil (ConPatIn con []) = con == getName nilDataCon
538 is_list (ListPatIn _) = True
541 return_list id q = id == consDataCon && (is_nil q || is_list q)
543 make_list p q | is_nil q = ListPatIn [p]
544 make_list p (ListPatIn ps) = ListPatIn (p:ps)
545 make_list _ _ = panic "Check.make_list: Invalid argument"
547 make_con :: TypecheckedPat -> ExhaustivePat -> ExhaustivePat
548 make_con (ConPat id _ _ _ _) (p:q:ps, constraints)
549 | return_list id q = (make_list p q : ps, constraints)
550 | isInfixCon id = ((ConOpPatIn p name fixity q) : ps, constraints)
551 where name = getName id
552 fixity = panic "Check.make_con: Guessing fixity"
554 make_con (ConPat id _ _ _ pats) (ps,constraints)
555 | isTupleCon id = (TuplePatIn pats_con True : rest_pats, constraints)
556 | isUnboxedTupleCon id = (TuplePatIn pats_con False : rest_pats, constraints)
557 | otherwise = (ConPatIn name pats_con : rest_pats, constraints)
558 where num_args = length pats
560 pats_con = take num_args ps
561 rest_pats = drop num_args ps
564 make_whole_con :: DataCon -> WarningPat
565 make_whole_con con | isInfixCon con = ConOpPatIn new_wild_pat name fixity new_wild_pat
566 | otherwise = ConPatIn name pats
568 fixity = panic "Check.make_whole_con: Guessing fixity"
570 arity = dataConSourceArity con
571 pats = take arity (repeat new_wild_pat)
574 new_wild_pat :: WarningPat
575 new_wild_pat = WildPatIn
578 This equation makes the same thing as @tidy@ in @Match.lhs@, the
579 difference is that here we can do all the tidy in one place and in the
580 @Match@ tidy it must be done one column each time due to bookkeeping
585 simplify_eqns :: [EquationInfo] -> [EquationInfo]
586 simplify_eqns [] = []
587 simplify_eqns ((EqnInfo n ctx pats result):qs) =
588 (EqnInfo n ctx pats' result) : simplify_eqns qs
590 pats' = map simplify_pat pats
592 simplify_pat :: TypecheckedPat -> TypecheckedPat
594 simplify_pat pat@(WildPat gt) = pat
595 simplify_pat (VarPat id) = WildPat (idType id)
597 simplify_pat (LazyPat p) = simplify_pat p
598 simplify_pat (AsPat id p) = simplify_pat p
600 simplify_pat (ConPat id ty tvs dicts ps) = ConPat id ty tvs dicts (map simplify_pat ps)
602 simplify_pat (ListPat ty ps) = foldr (\ x -> \y -> ConPat consDataCon list_ty [] [] [x, y])
603 (ConPat nilDataCon list_ty [] [] [])
604 (map simplify_pat ps)
605 where list_ty = mkListTy ty
608 simplify_pat (TuplePat ps True) = ConPat (tupleCon arity)
609 (mkTupleTy arity (map outPatType ps)) [] []
610 (map simplify_pat ps)
614 simplify_pat (TuplePat ps False)
615 = ConPat (unboxedTupleCon arity)
616 (mkUnboxedTupleTy arity (map outPatType ps)) [] []
617 (map simplify_pat ps)
621 simplify_pat (RecPat dc ty ex_tvs dicts [])
622 = ConPat dc ty ex_tvs dicts all_wild_pats
624 all_wild_pats = map WildPat con_arg_tys
626 -- identical to machinations in Match.tidy1:
627 (_, inst_tys, _) = splitAlgTyConApp ty
628 con_arg_tys = dataConArgTys dc (inst_tys ++ mkTyVarTys ex_tvs)
630 simplify_pat (RecPat dc ty ex_tvs dicts idps)
631 = ConPat dc ty ex_tvs dicts pats
633 pats = map (simplify_pat.snd) all_pats
635 -- pad out all the missing fields with WildPats.
636 field_pats = map (\ f -> (getName f, WildPat (panic "simplify_pat(RecPat-2)")))
637 (dataConFieldLabels dc)
640 ( \ (id,p,_) acc -> insertNm (getName id) p acc)
644 insertNm nm p [] = [(nm,p)]
645 insertNm nm p (x@(n,_):xs)
646 | nm == n = (nm,p):xs
647 | otherwise = x : insertNm nm p xs
649 simplify_pat pat@(LitPat lit lit_ty) = tidyLitPat lit lit_ty pat
650 simplify_pat pat@(NPat lit lit_ty hsexpr) = tidyLitPat lit lit_ty pat
652 simplify_pat (NPlusKPat id hslit ty hsexpr1 hsexpr2) =
654 where ty = panic "Check.simplify_pat: Gessing ty"
656 simplify_pat (DictPat dicts methods) =
657 case num_of_d_and_ms of
658 0 -> simplify_pat (TuplePat [] True)
659 1 -> simplify_pat (head dict_and_method_pats)
660 _ -> simplify_pat (TuplePat dict_and_method_pats True)
662 num_of_d_and_ms = length dicts + length methods
663 dict_and_method_pats = map VarPat (dicts ++ methods)