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, mkLocalName, 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 )
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 _ (TuplePatIn pats boxed) = TuplePatIn (map untidy_no_pars pats) boxed
147 untidy _ pat = pprPanic "Check.untidy: SigPatIn" (ppr pat)
149 pars :: NeedPars -> WarningPat -> WarningPat
150 pars True p = ParPatIn p
153 untidy_lit :: HsLit -> HsLit
154 untidy_lit (HsCharPrim c) = HsChar c
155 --untidy_lit (HsStringPrim s) = HsString s
159 This equation is the same that check, the only difference is that the
160 boring work is done, that work needs to be done only once, this is
161 the reason top have two functions, check is the external interface,
162 @check'@ is called recursively.
164 There are several cases:
167 \item There are no equations: Everything is OK.
168 \item There are only one equation, that can fail, and all the patterns are
169 variables. Then that equation is used and the same equation is
171 \item All the patterns are variables, and the match can fail, there are
172 more equations then the results is the result of the rest of equations
173 and this equation is used also.
175 \item The general case, if all the patterns are variables (here the match
176 can't fail) then the result is that this equation is used and this
177 equation doesn't generate non-exhaustive cases.
179 \item In the general case, there can exist literals ,constructors or only
180 vars in the first column, we actuate in consequence.
187 check' :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
188 check' [] = ([([],[])],emptyUniqSet)
190 check' [EqnInfo n ctx ps (MatchResult CanFail _)]
191 | all_vars ps = ([(takeList ps (repeat new_wild_pat),[])], unitUniqSet n)
193 check' qs@((EqnInfo n ctx ps (MatchResult CanFail _)):rs)
194 | all_vars ps = (pats, addOneToUniqSet indexs n)
196 (pats,indexs) = check' rs
198 check' qs@((EqnInfo n ctx ps result):_)
199 | all_vars ps = ([], unitUniqSet n)
200 -- | nplusk = panic "Check.check': Work in progress: nplusk"
201 -- | npat = panic "Check.check': Work in progress: npat ?????"
202 | literals = split_by_literals qs
203 | constructors = split_by_constructor qs
204 | only_vars = first_column_only_vars qs
205 | otherwise = panic "Check.check': Not implemented :-("
207 -- Note: RecPats will have been simplified to ConPats
209 constructors = or (map is_con qs)
210 literals = or (map is_lit qs)
211 only_vars = and (map is_var qs)
212 -- npat = or (map is_npat qs)
213 -- nplusk = or (map is_nplusk qs)
216 Here begins the code to deal with literals, we need to split the matrix
217 in different matrix beginning by each literal and a last matrix with the
221 split_by_literals :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
222 split_by_literals qs = process_literals used_lits qs
224 used_lits = get_used_lits qs
227 @process_explicit_literals@ is a function that process each literal that appears
228 in the column of the matrix.
231 process_explicit_literals :: [HsLit] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
232 process_explicit_literals lits qs = (concat pats, unionManyUniqSets indexs)
234 pats_indexs = map (\x -> construct_literal_matrix x qs) lits
235 (pats,indexs) = unzip pats_indexs
240 @process_literals@ calls @process_explicit_literals@ to deal with the literals
241 that appears in the matrix and deal also with the rest of the cases. It
242 must be one Variable to be complete.
246 process_literals :: [HsLit] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
247 process_literals used_lits qs
248 | null default_eqns = ([make_row_vars used_lits (head qs)]++pats,indexs)
249 | otherwise = (pats_default,indexs_default)
251 (pats,indexs) = process_explicit_literals used_lits qs
252 default_eqns = (map remove_var (filter is_var 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))
267 new_lit = LitPatIn lit
269 remove_first_column_lit :: HsLit
272 remove_first_column_lit lit qs =
273 map shift_pat (filter (is_var_lit lit) qs)
275 shift_pat (EqnInfo n ctx [] result) = panic "Check.shift_var: no patterns"
276 shift_pat (EqnInfo n ctx (_:ps) result) = EqnInfo n ctx ps result
280 This function splits the equations @qs@ in groups that deal with the
285 split_by_constructor :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
287 split_by_constructor qs
288 | not (null unused_cons) = need_default_case used_cons unused_cons qs
289 | otherwise = no_need_default_case used_cons qs
291 used_cons = get_used_cons qs
292 unused_cons = get_unused_cons used_cons
296 The first column of the patterns matrix only have vars, then there is
300 first_column_only_vars :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
301 first_column_only_vars qs = (map (\ (xs,ys) -> (new_wild_pat:xs,ys)) pats,indexs)
303 (pats,indexs) = check' (map remove_var qs)
307 This equation takes a matrix of patterns and split the equations by
308 constructor, using all the constructors that appears in the first column
309 of the pattern matching.
311 We can need a default clause or not ...., it depends if we used all the
312 constructors or not explicitly. The reasoning is similar to @process_literals@,
313 the difference is that here the default case is not always needed.
316 no_need_default_case :: [TypecheckedPat] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
317 no_need_default_case cons qs = (concat pats, unionManyUniqSets indexs)
319 pats_indexs = map (\x -> construct_matrix x qs) cons
320 (pats,indexs) = unzip pats_indexs
322 need_default_case :: [TypecheckedPat] -> [DataCon] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
323 need_default_case used_cons unused_cons qs
324 | null default_eqns = (pats_default_no_eqns,indexs)
325 | otherwise = (pats_default,indexs_default)
327 (pats,indexs) = no_need_default_case used_cons qs
328 default_eqns = (map remove_var (filter is_var qs))
329 (pats',indexs') = check' default_eqns
330 pats_default = [(make_whole_con c:ps,constraints) |
331 c <- unused_cons, (ps,constraints) <- pats'] ++ pats
332 new_wilds = make_row_vars_for_constructor (head qs)
333 pats_default_no_eqns = [(make_whole_con c:new_wilds,[]) | c <- unused_cons] ++ pats
334 indexs_default = unionUniqSets indexs' indexs
336 construct_matrix :: TypecheckedPat -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
337 construct_matrix con qs =
338 (map (make_con con) pats,indexs)
340 (pats,indexs) = (check' (remove_first_column con qs))
343 Here remove first column is more difficult that with literals due to the fact
344 that constructors can have arguments.
346 For instance, the matrix
358 remove_first_column :: TypecheckedPat -- Constructor
361 remove_first_column (ConPat con _ _ _ con_pats) qs =
362 map shift_var (filter (is_var_con con) qs)
364 new_wilds = [WildPat (outPatType arg_pat) | arg_pat <- con_pats]
365 shift_var (EqnInfo n ctx (ConPat _ _ _ _ ps':ps) result) =
366 EqnInfo n ctx (ps'++ps) result
367 shift_var (EqnInfo n ctx (WildPat _ :ps) result) =
368 EqnInfo n ctx (new_wilds ++ ps) result
369 shift_var _ = panic "Check.Shift_var:No done"
371 make_row_vars :: [HsLit] -> EquationInfo -> ExhaustivePat
372 make_row_vars used_lits (EqnInfo _ _ pats _ ) =
373 (VarPatIn new_var:takeList (tail pats) (repeat new_wild_pat),[(new_var,used_lits)])
374 where new_var = hash_x
376 hash_x = mkLocalName unboundKey {- doesn't matter much -}
377 (mkVarOcc SLIT("#x"))
380 make_row_vars_for_constructor :: EquationInfo -> [WarningPat]
381 make_row_vars_for_constructor (EqnInfo _ _ pats _ ) = takeList (tail pats) (repeat new_wild_pat)
383 compare_cons :: TypecheckedPat -> TypecheckedPat -> Bool
384 compare_cons (ConPat id1 _ _ _ _) (ConPat id2 _ _ _ _) = id1 == id2
386 remove_dups :: [TypecheckedPat] -> [TypecheckedPat]
388 remove_dups (x:xs) | or (map (\y -> compare_cons x y) xs) = remove_dups xs
389 | otherwise = x : remove_dups xs
391 get_used_cons :: [EquationInfo] -> [TypecheckedPat]
392 get_used_cons qs = remove_dups [con | (EqnInfo _ _ (con@(ConPat _ _ _ _ _):_) _) <- qs ]
394 remove_dups' :: [HsLit] -> [HsLit]
396 remove_dups' (x:xs) | x `elem` xs = remove_dups' xs
397 | otherwise = x : remove_dups' xs
400 get_used_lits :: [EquationInfo] -> [HsLit]
401 get_used_lits qs = remove_dups' all_literals
403 all_literals = get_used_lits' qs
405 get_used_lits' :: [EquationInfo] -> [HsLit]
406 get_used_lits' [] = []
407 get_used_lits' ((EqnInfo _ _ ((LitPat lit _):_) _):qs) =
408 lit : get_used_lits qs
409 get_used_lits' ((EqnInfo _ _ ((NPat lit _ _):_) _):qs) =
410 lit : get_used_lits qs
411 get_used_lits' (q:qs) =
414 get_unused_cons :: [TypecheckedPat] -> [DataCon]
415 get_unused_cons used_cons = unused_cons
417 (ConPat _ ty _ _ _) = head used_cons
418 ty_con = tcTyConAppTyCon ty -- Newtype observable
419 all_cons = tyConDataCons ty_con
420 used_cons_as_id = map (\ (ConPat d _ _ _ _) -> d) used_cons
421 unused_cons = uniqSetToList
422 (mkUniqSet all_cons `minusUniqSet` mkUniqSet used_cons_as_id)
424 all_vars :: [TypecheckedPat] -> Bool
426 all_vars (WildPat _:ps) = all_vars ps
429 remove_var :: EquationInfo -> EquationInfo
430 remove_var (EqnInfo n ctx (WildPat _:ps) result) = EqnInfo n ctx ps result
432 panic "Check.remove_var: equation does not begin with a variable"
434 is_con :: EquationInfo -> Bool
435 is_con (EqnInfo _ _ ((ConPat _ _ _ _ _):_) _) = True
438 is_lit :: EquationInfo -> Bool
439 is_lit (EqnInfo _ _ ((LitPat _ _):_) _) = True
440 is_lit (EqnInfo _ _ ((NPat _ _ _):_) _) = True
443 is_npat :: EquationInfo -> Bool
444 is_npat (EqnInfo _ _ ((NPat _ _ _):_) _) = True
447 is_nplusk :: EquationInfo -> Bool
448 is_nplusk (EqnInfo _ _ ((NPlusKPat _ _ _ _ _):_) _) = True
451 is_var :: EquationInfo -> Bool
452 is_var (EqnInfo _ _ ((WildPat _):_) _) = True
455 is_var_con :: DataCon -> EquationInfo -> Bool
456 is_var_con con (EqnInfo _ _ ((WildPat _):_) _) = True
457 is_var_con con (EqnInfo _ _ ((ConPat id _ _ _ _):_) _) | id == con = True
458 is_var_con con _ = False
460 is_var_lit :: HsLit -> EquationInfo -> Bool
461 is_var_lit lit (EqnInfo _ _ ((WildPat _):_) _) = True
462 is_var_lit lit (EqnInfo _ _ ((LitPat lit' _):_) _) | lit == lit' = True
463 is_var_lit lit (EqnInfo _ _ ((NPat lit' _ _):_) _) | lit == lit' = True
464 is_var_lit lit _ = False
467 The difference beteewn @make_con@ and @make_whole_con@ is that
468 @make_wole_con@ creates a new constructor with all their arguments, and
469 @make_con@ takes a list of argumntes, creates the contructor getting their
470 arguments from the list. See where \fbox{\ ???\ } are used for details.
472 We need to reconstruct the patterns (make the constructors infix and
473 similar) at the same time that we create the constructors.
475 You can tell tuple constructors using
479 You can see if one constructor is infix with this clearer code :-))))))))))
481 Lex.isLexConSym (Name.occNameString (Name.getOccName con))
484 Rather clumsy but it works. (Simon Peyton Jones)
487 We don't mind the @nilDataCon@ because it doesn't change the way to
488 print the messsage, we are searching only for things like: @[1,2,3]@,
491 In @reconstruct_pat@ we want to ``undo'' the work
492 that we have done in @simplify_pat@.
495 @((,) x y)@ & returns to be & @(x, y)@
496 \\ @((:) x xs)@ & returns to be & @(x:xs)@
497 \\ @(x:(...:[])@ & returns to be & @[x,...]@
500 The difficult case is the third one becouse we need to follow all the
501 contructors until the @[]@ to know that we need to use the second case,
502 not the second. \fbox{\ ???\ }
505 isInfixCon con = isDataSymOcc (getOccName con)
507 is_nil (ConPatIn con []) = con == getName nilDataCon
510 is_list (ListPatIn _) = True
513 return_list id q = id == consDataCon && (is_nil q || is_list q)
515 make_list p q | is_nil q = ListPatIn [p]
516 make_list p (ListPatIn ps) = ListPatIn (p:ps)
517 make_list _ _ = panic "Check.make_list: Invalid argument"
519 make_con :: TypecheckedPat -> ExhaustivePat -> ExhaustivePat
520 make_con (ConPat id _ _ _ _) (p:q:ps, constraints)
521 | return_list id q = (make_list p q : ps, constraints)
522 | isInfixCon id = ((ConOpPatIn p name fixity q) : ps, constraints)
523 where name = getName id
524 fixity = panic "Check.make_con: Guessing fixity"
526 make_con (ConPat id _ _ _ pats) (ps,constraints)
527 | isTupleTyCon tc = (TuplePatIn pats_con (tupleTyConBoxity tc) : rest_pats, constraints)
528 | otherwise = (ConPatIn name pats_con : rest_pats, constraints)
529 where name = getName id
530 (pats_con, rest_pats) = splitAtList pats ps
534 make_whole_con :: DataCon -> WarningPat
535 make_whole_con con | isInfixCon con = ConOpPatIn new_wild_pat name fixity new_wild_pat
536 | otherwise = ConPatIn name pats
538 fixity = panic "Check.make_whole_con: Guessing fixity"
540 arity = dataConSourceArity con
541 pats = replicate arity new_wild_pat
544 new_wild_pat :: WarningPat
545 new_wild_pat = WildPatIn
548 This equation makes the same thing as @tidy@ in @Match.lhs@, the
549 difference is that here we can do all the tidy in one place and in the
550 @Match@ tidy it must be done one column each time due to bookkeeping
555 simplify_eqns :: [EquationInfo] -> [EquationInfo]
556 simplify_eqns [] = []
557 simplify_eqns ((EqnInfo n ctx pats result):qs) =
558 (EqnInfo n ctx pats' result) : simplify_eqns qs
560 pats' = map simplify_pat pats
562 simplify_pat :: TypecheckedPat -> TypecheckedPat
564 simplify_pat pat@(WildPat gt) = pat
565 simplify_pat (VarPat id) = WildPat (idType id)
567 simplify_pat (LazyPat p) = simplify_pat p
568 simplify_pat (AsPat id p) = simplify_pat p
569 simplify_pat (SigPat p ty fn) = simplify_pat p -- I'm not sure this is right
571 simplify_pat (ConPat id ty tvs dicts ps) = ConPat id ty tvs dicts (map simplify_pat ps)
573 simplify_pat (ListPat ty ps) = foldr (\ x -> \y -> ConPat consDataCon list_ty [] [] [x, y])
574 (ConPat nilDataCon list_ty [] [] [])
575 (map simplify_pat ps)
576 where list_ty = mkListTy ty
579 simplify_pat (TuplePat ps boxity)
580 = ConPat (tupleCon boxity arity)
581 (mkTupleTy boxity arity (map outPatType ps)) [] []
582 (map simplify_pat ps)
586 simplify_pat (RecPat dc ty ex_tvs dicts [])
587 = ConPat dc ty ex_tvs dicts all_wild_pats
589 all_wild_pats = map WildPat con_arg_tys
591 -- Identical to machinations in Match.tidy1:
592 inst_tys = tcTyConAppArgs ty -- Newtype is observable
593 con_arg_tys = dataConArgTys dc (inst_tys ++ mkTyVarTys ex_tvs)
595 simplify_pat (RecPat dc ty ex_tvs dicts idps)
596 = ConPat dc ty ex_tvs dicts pats
598 pats = map (simplify_pat.snd) all_pats
600 -- pad out all the missing fields with WildPats.
601 field_pats = map (\ f -> (getName f, WildPat (panic "simplify_pat(RecPat-2)")))
602 (dataConFieldLabels dc)
605 ( \ (id,p,_) acc -> insertNm (getName id) p acc)
609 insertNm nm p [] = [(nm,p)]
610 insertNm nm p (x@(n,_):xs)
611 | nm == n = (nm,p):xs
612 | otherwise = x : insertNm nm p xs
614 simplify_pat pat@(LitPat lit lit_ty) = tidyLitPat lit pat
616 -- unpack string patterns fully, so we can see when they overlap with
617 -- each other, or even explicit lists of Chars.
618 simplify_pat pat@(NPat (HsString s) _ _) =
619 foldr (\c pat -> ConPat consDataCon stringTy [] [] [mk_char_lit c,pat])
620 (ConPat nilDataCon stringTy [] [] []) (_UNPK_INT_ s)
622 mk_char_lit c = ConPat charDataCon charTy [] []
623 [LitPat (HsCharPrim c) charPrimTy]
625 simplify_pat pat@(NPat lit lit_ty hsexpr) = tidyNPat lit lit_ty pat
627 simplify_pat (NPlusKPat id hslit ty hsexpr1 hsexpr2) =
629 where ty = panic "Check.simplify_pat: Gessing ty"
631 simplify_pat (DictPat dicts methods) =
632 case num_of_d_and_ms of
633 0 -> simplify_pat (TuplePat [] Boxed)
634 1 -> simplify_pat (head dict_and_method_pats)
635 _ -> simplify_pat (TuplePat dict_and_method_pats Boxed)
637 num_of_d_and_ms = length dicts + length methods
638 dict_and_method_pats = map VarPat (dicts ++ methods)