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, outPatType )
15 import TcType ( tcTyConAppTyCon, tcTyConAppArgs )
16 import DsUtils ( EquationInfo(..), MatchResult(..), EqnSet,
17 CanItFail(..), tidyLitPat, tidyNPat,
20 import DataCon ( DataCon, dataConTyCon, dataConArgTys,
21 dataConSourceArity, dataConFieldLabels )
22 import Name ( Name, mkInternalName, getOccName, isDataSymOcc, getName, mkVarOcc )
23 import TcType ( mkTyVarTys )
24 import TysPrim ( charPrimTy )
26 import PrelNames ( unboundKey )
27 import TyCon ( tyConDataCons, tupleTyConBoxity, isTupleTyCon )
28 import BasicTypes ( Boxity(..) )
29 import SrcLoc ( noSrcLoc )
31 import Util ( takeList, splitAtList, notNull )
34 #include "HsVersions.h"
37 This module performs checks about if one list of equations are:
42 To discover that we go through the list of equations in a tree-like fashion.
44 If you like theory, a similar algorithm is described in:
46 {\em Two Techniques for Compiling Lazy Pattern Matching},
48 INRIA Rocquencourt (RR-2385, 1994)
50 The algorithm is based on the first technique, but there are some differences:
52 \item We don't generate code
53 \item We have constructors and literals (not only literals as in the
55 \item We don't use directions, we must select the columns from
58 (By the way the second technique is really similar to the one used in
59 @Match.lhs@ to generate code)
61 This function takes the equations of a pattern and returns:
63 \item The patterns that are not recognized
64 \item The equations that are not overlapped
66 It simplify the patterns and then call @check'@ (the same semantics), and it
67 needs to reconstruct the patterns again ....
69 The problem appear with things like:
74 We want to put the two patterns with the same syntax, (prefix form) and
75 then all the constructors are equal:
77 f (: x (: y [])) = ....
80 (more about that in @simplify_eqns@)
82 We would prefer to have a @WarningPat@ of type @String@, but Strings and the
83 Pretty Printer are not friends.
85 We use @InPat@ in @WarningPat@ instead of @OutPat@
86 because we need to print the
87 warning messages in the same way they are introduced, i.e. if the user
92 He don't want a warning message written:
94 f (: x (: y [])) ........
96 Then we need to use InPats.
98 Juan Quintela 5 JUL 1998\\
99 User-friendliness and compiler writers are no friends.
103 type WarningPat = InPat Name
104 type ExhaustivePat = ([WarningPat], [(Name, [HsLit])])
107 check :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
108 check qs = (untidy_warns, incomplete)
110 (warns, incomplete) = check' (simplify_eqns qs)
111 untidy_warns = map untidy_exhaustive warns
113 untidy_exhaustive :: ExhaustivePat -> ExhaustivePat
114 untidy_exhaustive ([pat], messages) =
115 ([untidy_no_pars pat], map untidy_message messages)
116 untidy_exhaustive (pats, messages) =
117 (map untidy_pars pats, map untidy_message messages)
119 untidy_message :: (Name, [HsLit]) -> (Name, [HsLit])
120 untidy_message (string, lits) = (string, map untidy_lit lits)
123 The function @untidy@ does the reverse work of the @simplify_pat@ funcion.
129 untidy_no_pars :: WarningPat -> WarningPat
130 untidy_no_pars p = untidy False p
132 untidy_pars :: WarningPat -> WarningPat
133 untidy_pars p = untidy True p
135 untidy :: NeedPars -> WarningPat -> WarningPat
136 untidy _ p@WildPatIn = p
137 untidy _ p@(VarPatIn name) = p
138 untidy _ (LitPatIn lit) = LitPatIn (untidy_lit lit)
139 untidy _ p@(ConPatIn name []) = p
140 untidy b (ConPatIn name pats) =
141 pars b (ConPatIn name (map untidy_pars pats))
142 untidy b (ConOpPatIn pat1 name fixity pat2) =
143 pars b (ConOpPatIn (untidy_pars pat1) name fixity (untidy_pars pat2))
144 untidy _ (ListPatIn pats) = ListPatIn (map untidy_no_pars pats)
145 untidy _ (PArrPatIn pats) =
146 panic "Check.untidy: Shouldn't get a parallel array here!"
147 untidy _ (TuplePatIn pats boxed) = TuplePatIn (map untidy_no_pars pats) boxed
149 untidy _ pat = pprPanic "Check.untidy: SigPatIn" (ppr pat)
151 pars :: NeedPars -> WarningPat -> WarningPat
152 pars True p = ParPatIn p
155 untidy_lit :: HsLit -> HsLit
156 untidy_lit (HsCharPrim c) = HsChar c
157 --untidy_lit (HsStringPrim s) = HsString s
161 This equation is the same that check, the only difference is that the
162 boring work is done, that work needs to be done only once, this is
163 the reason top have two functions, check is the external interface,
164 @check'@ is called recursively.
166 There are several cases:
169 \item There are no equations: Everything is OK.
170 \item There are only one equation, that can fail, and all the patterns are
171 variables. Then that equation is used and the same equation is
173 \item All the patterns are variables, and the match can fail, there are
174 more equations then the results is the result of the rest of equations
175 and this equation is used also.
177 \item The general case, if all the patterns are variables (here the match
178 can't fail) then the result is that this equation is used and this
179 equation doesn't generate non-exhaustive cases.
181 \item In the general case, there can exist literals ,constructors or only
182 vars in the first column, we actuate in consequence.
189 check' :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
190 check' [] = ([([],[])],emptyUniqSet)
192 check' [EqnInfo n ctx ps (MatchResult CanFail _)]
193 | all_vars ps = ([(takeList ps (repeat new_wild_pat),[])], unitUniqSet n)
195 check' qs@((EqnInfo n ctx ps (MatchResult CanFail _)):rs)
196 | all_vars ps = (pats, addOneToUniqSet indexs n)
198 (pats,indexs) = check' rs
200 check' qs@((EqnInfo n ctx ps result):_)
201 | all_vars ps = ([], unitUniqSet n)
202 -- | nplusk = panic "Check.check': Work in progress: nplusk"
203 -- | npat = panic "Check.check': Work in progress: npat ?????"
204 | literals = split_by_literals qs
205 | constructors = split_by_constructor qs
206 | only_vars = first_column_only_vars qs
207 | otherwise = panic "Check.check': Not implemented :-("
209 -- Note: RecPats will have been simplified to ConPats
211 constructors = or (map is_con qs)
212 literals = or (map is_lit qs)
213 only_vars = and (map is_var qs)
214 -- npat = or (map is_npat qs)
215 -- nplusk = or (map is_nplusk qs)
218 Here begins the code to deal with literals, we need to split the matrix
219 in different matrix beginning by each literal and a last matrix with the
223 split_by_literals :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
224 split_by_literals qs = process_literals used_lits qs
226 used_lits = get_used_lits qs
229 @process_explicit_literals@ is a function that process each literal that appears
230 in the column of the matrix.
233 process_explicit_literals :: [HsLit] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
234 process_explicit_literals lits qs = (concat pats, unionManyUniqSets indexs)
236 pats_indexs = map (\x -> construct_literal_matrix x qs) lits
237 (pats,indexs) = unzip pats_indexs
242 @process_literals@ calls @process_explicit_literals@ to deal with the literals
243 that appears in the matrix and deal also with the rest of the cases. It
244 must be one Variable to be complete.
248 process_literals :: [HsLit] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
249 process_literals used_lits qs
250 | null default_eqns = ([make_row_vars used_lits (head qs)]++pats,indexs)
251 | otherwise = (pats_default,indexs_default)
253 (pats,indexs) = process_explicit_literals used_lits qs
254 default_eqns = (map remove_var (filter is_var qs))
255 (pats',indexs') = check' default_eqns
256 pats_default = [(new_wild_pat:ps,constraints) | (ps,constraints) <- (pats')] ++ pats
257 indexs_default = unionUniqSets indexs' indexs
260 Here we have selected the literal and we will select all the equations that
261 begins for that literal and create a new matrix.
264 construct_literal_matrix :: HsLit -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
265 construct_literal_matrix lit qs =
266 (map (\ (xs,ys) -> (new_lit:xs,ys)) pats,indexs)
268 (pats,indexs) = (check' (remove_first_column_lit lit qs))
269 new_lit = LitPatIn lit
271 remove_first_column_lit :: HsLit
274 remove_first_column_lit lit qs =
275 map shift_pat (filter (is_var_lit lit) qs)
277 shift_pat (EqnInfo n ctx [] result) = panic "Check.shift_var: no patterns"
278 shift_pat (EqnInfo n ctx (_:ps) result) = EqnInfo n ctx ps result
282 This function splits the equations @qs@ in groups that deal with the
287 split_by_constructor :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
289 split_by_constructor qs
290 | notNull unused_cons = need_default_case used_cons unused_cons qs
291 | otherwise = no_need_default_case used_cons qs
293 used_cons = get_used_cons qs
294 unused_cons = get_unused_cons used_cons
298 The first column of the patterns matrix only have vars, then there is
302 first_column_only_vars :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
303 first_column_only_vars qs = (map (\ (xs,ys) -> (new_wild_pat:xs,ys)) pats,indexs)
305 (pats,indexs) = check' (map remove_var qs)
309 This equation takes a matrix of patterns and split the equations by
310 constructor, using all the constructors that appears in the first column
311 of the pattern matching.
313 We can need a default clause or not ...., it depends if we used all the
314 constructors or not explicitly. The reasoning is similar to @process_literals@,
315 the difference is that here the default case is not always needed.
318 no_need_default_case :: [TypecheckedPat] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
319 no_need_default_case cons qs = (concat pats, unionManyUniqSets indexs)
321 pats_indexs = map (\x -> construct_matrix x qs) cons
322 (pats,indexs) = unzip pats_indexs
324 need_default_case :: [TypecheckedPat] -> [DataCon] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
325 need_default_case used_cons unused_cons qs
326 | null default_eqns = (pats_default_no_eqns,indexs)
327 | otherwise = (pats_default,indexs_default)
329 (pats,indexs) = no_need_default_case used_cons qs
330 default_eqns = (map remove_var (filter is_var qs))
331 (pats',indexs') = check' default_eqns
332 pats_default = [(make_whole_con c:ps,constraints) |
333 c <- unused_cons, (ps,constraints) <- pats'] ++ pats
334 new_wilds = make_row_vars_for_constructor (head qs)
335 pats_default_no_eqns = [(make_whole_con c:new_wilds,[]) | c <- unused_cons] ++ pats
336 indexs_default = unionUniqSets indexs' indexs
338 construct_matrix :: TypecheckedPat -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
339 construct_matrix con qs =
340 (map (make_con con) pats,indexs)
342 (pats,indexs) = (check' (remove_first_column con qs))
345 Here remove first column is more difficult that with literals due to the fact
346 that constructors can have arguments.
348 For instance, the matrix
360 remove_first_column :: TypecheckedPat -- Constructor
363 remove_first_column (ConPat con _ _ _ con_pats) qs =
364 map shift_var (filter (is_var_con con) qs)
366 new_wilds = [WildPat (outPatType arg_pat) | arg_pat <- con_pats]
367 shift_var (EqnInfo n ctx (ConPat _ _ _ _ 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 (VarPatIn 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 SLIT("#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 (ConPat id1 _ _ _ _) (ConPat 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@(ConPat _ _ _ _ _):_) _) <- 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 _ _ ((NPat 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 (ConPat _ ty _ _ _) = head used_cons
420 ty_con = tcTyConAppTyCon ty -- Newtype observable
421 all_cons = tyConDataCons ty_con
422 used_cons_as_id = map (\ (ConPat 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 is_con :: EquationInfo -> Bool
437 is_con (EqnInfo _ _ ((ConPat _ _ _ _ _):_) _) = True
440 is_lit :: EquationInfo -> Bool
441 is_lit (EqnInfo _ _ ((LitPat _ _):_) _) = True
442 is_lit (EqnInfo _ _ ((NPat _ _ _):_) _) = True
445 is_npat :: EquationInfo -> Bool
446 is_npat (EqnInfo _ _ ((NPat _ _ _):_) _) = True
449 is_nplusk :: EquationInfo -> Bool
450 is_nplusk (EqnInfo _ _ ((NPlusKPat _ _ _ _ _):_) _) = True
453 is_var :: EquationInfo -> Bool
454 is_var (EqnInfo _ _ ((WildPat _):_) _) = True
457 is_var_con :: DataCon -> EquationInfo -> Bool
458 is_var_con con (EqnInfo _ _ ((WildPat _):_) _) = True
459 is_var_con con (EqnInfo _ _ ((ConPat id _ _ _ _):_) _) | id == con = True
460 is_var_con con _ = False
462 is_var_lit :: HsLit -> EquationInfo -> Bool
463 is_var_lit lit (EqnInfo _ _ ((WildPat _):_) _) = True
464 is_var_lit lit (EqnInfo _ _ ((LitPat lit' _):_) _) | lit == lit' = True
465 is_var_lit lit (EqnInfo _ _ ((NPat lit' _ _):_) _) | lit == lit' = True
466 is_var_lit lit _ = False
469 The difference beteewn @make_con@ and @make_whole_con@ is that
470 @make_wole_con@ creates a new constructor with all their arguments, and
471 @make_con@ takes a list of argumntes, creates the contructor getting their
472 arguments from the list. See where \fbox{\ ???\ } are used for details.
474 We need to reconstruct the patterns (make the constructors infix and
475 similar) at the same time that we create the constructors.
477 You can tell tuple constructors using
481 You can see if one constructor is infix with this clearer code :-))))))))))
483 Lex.isLexConSym (Name.occNameString (Name.getOccName con))
486 Rather clumsy but it works. (Simon Peyton Jones)
489 We don't mind the @nilDataCon@ because it doesn't change the way to
490 print the messsage, we are searching only for things like: @[1,2,3]@,
493 In @reconstruct_pat@ we want to ``undo'' the work
494 that we have done in @simplify_pat@.
497 @((,) x y)@ & returns to be & @(x, y)@
498 \\ @((:) x xs)@ & returns to be & @(x:xs)@
499 \\ @(x:(...:[])@ & returns to be & @[x,...]@
502 The difficult case is the third one becouse we need to follow all the
503 contructors until the @[]@ to know that we need to use the second case,
504 not the second. \fbox{\ ???\ }
507 isInfixCon con = isDataSymOcc (getOccName con)
509 is_nil (ConPatIn con []) = con == getName nilDataCon
512 is_list (ListPatIn _) = True
515 return_list id q = id == consDataCon && (is_nil q || is_list q)
517 make_list p q | is_nil q = ListPatIn [p]
518 make_list p (ListPatIn ps) = ListPatIn (p:ps)
519 make_list _ _ = panic "Check.make_list: Invalid argument"
521 make_con :: TypecheckedPat -> ExhaustivePat -> ExhaustivePat
522 make_con (ConPat id _ _ _ _) (p:q:ps, constraints)
523 | return_list id q = (make_list p q : ps, constraints)
524 | isInfixCon id = ((ConOpPatIn p name fixity q) : ps, constraints)
525 where name = getName id
526 fixity = panic "Check.make_con: Guessing fixity"
528 make_con (ConPat id _ _ _ pats) (ps, constraints)
529 | isTupleTyCon tc = (TuplePatIn pats_con (tupleTyConBoxity tc) : rest_pats, constraints)
530 | otherwise = (ConPatIn name pats_con : rest_pats, constraints)
531 where name = getName id
532 (pats_con, rest_pats) = splitAtList pats ps
535 -- reconstruct parallel array pattern
537 -- * don't check for the type only; we need to make sure that we are really
538 -- dealing with one of the fake constructors and not with the real
541 make_con (ConPat id _ _ _ pats) (ps, constraints)
542 | isPArrFakeCon id = (PArrPatIn patsCon : restPats, constraints)
543 | otherwise = (ConPatIn name patsCon : restPats, constraints)
546 (patsCon, restPats) = splitAtList pats ps
550 make_whole_con :: DataCon -> WarningPat
551 make_whole_con con | isInfixCon con = ConOpPatIn new_wild_pat name fixity new_wild_pat
552 | otherwise = ConPatIn name pats
554 fixity = panic "Check.make_whole_con: Guessing fixity"
556 arity = dataConSourceArity con
557 pats = replicate arity new_wild_pat
560 new_wild_pat :: WarningPat
561 new_wild_pat = WildPatIn
564 This equation makes the same thing as @tidy@ in @Match.lhs@, the
565 difference is that here we can do all the tidy in one place and in the
566 @Match@ tidy it must be done one column each time due to bookkeeping
571 simplify_eqns :: [EquationInfo] -> [EquationInfo]
572 simplify_eqns [] = []
573 simplify_eqns ((EqnInfo n ctx pats result):qs) =
574 (EqnInfo n ctx pats' result) : simplify_eqns qs
576 pats' = map simplify_pat pats
578 simplify_pat :: TypecheckedPat -> TypecheckedPat
580 simplify_pat pat@(WildPat gt) = pat
581 simplify_pat (VarPat id) = WildPat (idType id)
583 simplify_pat (LazyPat p) = simplify_pat p
584 simplify_pat (AsPat id p) = simplify_pat p
585 simplify_pat (SigPat p ty fn) = simplify_pat p -- I'm not sure this is right
587 simplify_pat (ConPat id ty tvs dicts ps) = ConPat id ty tvs dicts (map simplify_pat ps)
589 simplify_pat (ListPat ty ps) = foldr (\ x -> \y -> ConPat consDataCon list_ty [] [] [x, y])
590 (ConPat nilDataCon list_ty [] [] [])
591 (map simplify_pat ps)
592 where list_ty = mkListTy ty
594 -- introduce fake parallel array constructors to be able to handle parallel
595 -- arrays with the existing machinery for constructor pattern
597 simplify_pat (PArrPat ty ps)
598 = ConPat (parrFakeCon arity) (mkPArrTy ty) [] [] (map simplify_pat ps)
602 simplify_pat (TuplePat ps boxity)
603 = ConPat (tupleCon boxity arity)
604 (mkTupleTy boxity arity (map outPatType ps)) [] []
605 (map simplify_pat ps)
609 simplify_pat (RecPat dc ty ex_tvs dicts [])
610 = ConPat dc ty ex_tvs dicts all_wild_pats
612 all_wild_pats = map WildPat con_arg_tys
614 -- Identical to machinations in Match.tidy1:
615 inst_tys = tcTyConAppArgs ty -- Newtype is observable
616 con_arg_tys = dataConArgTys dc (inst_tys ++ mkTyVarTys ex_tvs)
618 simplify_pat (RecPat dc ty ex_tvs dicts idps)
619 = ConPat dc ty ex_tvs dicts pats
621 pats = map (simplify_pat.snd) all_pats
623 -- pad out all the missing fields with WildPats.
624 field_pats = map (\ f -> (getName f, WildPat (panic "simplify_pat(RecPat-2)")))
625 (dataConFieldLabels dc)
628 ( \ (id,p,_) acc -> insertNm (getName id) p acc)
632 insertNm nm p [] = [(nm,p)]
633 insertNm nm p (x@(n,_):xs)
634 | nm == n = (nm,p):xs
635 | otherwise = x : insertNm nm p xs
637 simplify_pat pat@(LitPat lit lit_ty) = tidyLitPat lit pat
639 -- unpack string patterns fully, so we can see when they overlap with
640 -- each other, or even explicit lists of Chars.
641 simplify_pat pat@(NPat (HsString s) _ _) =
642 foldr (\c pat -> ConPat consDataCon stringTy [] [] [mk_char_lit c,pat])
643 (ConPat nilDataCon stringTy [] [] []) (_UNPK_INT_ s)
645 mk_char_lit c = ConPat charDataCon charTy [] []
646 [LitPat (HsCharPrim c) charPrimTy]
648 simplify_pat pat@(NPat lit lit_ty hsexpr) = tidyNPat lit lit_ty pat
650 simplify_pat (NPlusKPat id hslit ty hsexpr1 hsexpr2) =
652 where ty = panic "Check.simplify_pat: Gessing ty"
654 simplify_pat (DictPat dicts methods) =
655 case num_of_d_and_ms of
656 0 -> simplify_pat (TuplePat [] Boxed)
657 1 -> simplify_pat (head dict_and_method_pats)
658 _ -> simplify_pat (TuplePat dict_and_method_pats Boxed)
660 num_of_d_and_ms = length dicts + length methods
661 dict_and_method_pats = map VarPat (dicts ++ methods)