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 ( hsPatType )
15 import TcType ( tcTyConAppTyCon )
16 import DsUtils ( EquationInfo(..), MatchResult(..), EqnSet,
17 CanItFail(..), tidyLitPat, tidyNPat,
19 import Id ( Id, idType )
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, Located(..), unLoc, noLoc )
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 b (L loc p) = L loc (untidy' b p)
136 untidy' _ p@(WildPat _) = p
137 untidy' _ p@(VarPat name) = p
138 untidy' _ (LitPat lit) = LitPat (untidy_lit lit)
139 untidy' _ p@(ConPatIn name (PrefixCon [])) = p
140 untidy' b (ConPatIn name ps) = pars b (L loc (ConPatIn name (untidy_con ps)))
141 untidy' _ (ListPat pats ty) = ListPat (map untidy_no_pars pats) ty
142 untidy' _ (TuplePat pats boxed) = TuplePat (map untidy_no_pars pats) boxed
143 untidy' _ (PArrPat _ _) = panic "Check.untidy: Shouldn't get a parallel array here!"
144 untidy' _ (SigPatIn _ _) = panic "Check.untidy: SigPat"
146 untidy_con (PrefixCon pats) = PrefixCon (map untidy_pars pats)
147 untidy_con (InfixCon p1 p2) = InfixCon (untidy_pars p1) (untidy_pars p2)
148 untidy_con (RecCon bs) = RecCon [(f,untidy_pars p) | (f,p) <- bs]
150 pars :: NeedPars -> WarningPat -> Pat Name
151 pars True p = ParPat p
154 untidy_lit :: HsLit -> HsLit
155 untidy_lit (HsCharPrim c) = HsChar c
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 nlWildPat),[])], 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 = pprPanic "Check.check': Not implemented :-(" (ppr first_pats)
207 -- Note: RecPats will have been simplified to ConPats
209 first_pats = ASSERT2( okGroup qs, pprGroup qs ) map firstPat qs
210 constructors = any is_con first_pats
211 literals = any is_lit first_pats
212 only_vars = all is_var first_pats
213 -- npat = or (map is_npat qs)
214 -- nplusk = or (map is_nplusk qs)
217 Here begins the code to deal with literals, we need to split the matrix
218 in different matrix beginning by each literal and a last matrix with the
222 split_by_literals :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
223 split_by_literals qs = process_literals used_lits qs
225 used_lits = get_used_lits qs
228 @process_explicit_literals@ is a function that process each literal that appears
229 in the column of the matrix.
232 process_explicit_literals :: [HsLit] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
233 process_explicit_literals lits qs = (concat pats, unionManyUniqSets indexs)
235 pats_indexs = map (\x -> construct_literal_matrix x qs) lits
236 (pats,indexs) = unzip pats_indexs
241 @process_literals@ calls @process_explicit_literals@ to deal with the literals
242 that appears in the matrix and deal also with the rest of the cases. It
243 must be one Variable to be complete.
247 process_literals :: [HsLit] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
248 process_literals used_lits qs
249 | null default_eqns = ([make_row_vars used_lits (head qs)]++pats,indexs)
250 | otherwise = (pats_default,indexs_default)
252 (pats,indexs) = process_explicit_literals used_lits qs
253 default_eqns = ASSERT2( okGroup qs, pprGroup qs )
254 map remove_var (filter (is_var . firstPat) qs)
255 (pats',indexs') = check' default_eqns
256 pats_default = [(nlWildPat: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 = nlLitPat lit
271 remove_first_column_lit :: HsLit
274 remove_first_column_lit lit qs
275 = ASSERT2( okGroup qs, pprGroup qs )
276 map shift_pat (filter (is_var_lit lit . firstPat) qs)
278 shift_pat (EqnInfo n ctx [] result) = panic "Check.shift_var: no patterns"
279 shift_pat (EqnInfo n ctx (_:ps) result) = EqnInfo n ctx ps result
283 This function splits the equations @qs@ in groups that deal with the
288 split_by_constructor :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
290 split_by_constructor qs
291 | notNull unused_cons = need_default_case used_cons unused_cons qs
292 | otherwise = no_need_default_case used_cons qs
294 used_cons = get_used_cons qs
295 unused_cons = get_unused_cons used_cons
299 The first column of the patterns matrix only have vars, then there is
303 first_column_only_vars :: [EquationInfo] -> ([ExhaustivePat],EqnSet)
304 first_column_only_vars qs = (map (\ (xs,ys) -> (nlWildPat:xs,ys)) pats,indexs)
306 (pats,indexs) = check' (map remove_var qs)
310 This equation takes a matrix of patterns and split the equations by
311 constructor, using all the constructors that appears in the first column
312 of the pattern matching.
314 We can need a default clause or not ...., it depends if we used all the
315 constructors or not explicitly. The reasoning is similar to @process_literals@,
316 the difference is that here the default case is not always needed.
319 no_need_default_case :: [Pat Id] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
320 no_need_default_case cons qs = (concat pats, unionManyUniqSets indexs)
322 pats_indexs = map (\x -> construct_matrix x qs) cons
323 (pats,indexs) = unzip pats_indexs
325 need_default_case :: [Pat Id] -> [DataCon] -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
326 need_default_case used_cons unused_cons qs
327 | null default_eqns = (pats_default_no_eqns,indexs)
328 | otherwise = (pats_default,indexs_default)
330 (pats,indexs) = no_need_default_case used_cons qs
331 default_eqns = ASSERT2( okGroup qs, pprGroup qs ) map remove_var (filter (is_var . firstPat) qs)
332 (pats',indexs') = check' default_eqns
333 pats_default = [(make_whole_con c:ps,constraints) |
334 c <- unused_cons, (ps,constraints) <- pats'] ++ pats
335 new_wilds = make_row_vars_for_constructor (head qs)
336 pats_default_no_eqns = [(make_whole_con c:new_wilds,[]) | c <- unused_cons] ++ pats
337 indexs_default = unionUniqSets indexs' indexs
339 construct_matrix :: Pat Id -> [EquationInfo] -> ([ExhaustivePat],EqnSet)
340 construct_matrix con qs =
341 (map (make_con con) pats,indexs)
343 (pats,indexs) = (check' (remove_first_column con qs))
346 Here remove first column is more difficult that with literals due to the fact
347 that constructors can have arguments.
349 For instance, the matrix
361 remove_first_column :: Pat Id -- Constructor
364 remove_first_column (ConPatOut con (PrefixCon con_pats) _ _ _) qs
365 = ASSERT2( okGroup qs, pprGroup qs )
366 map shift_var (filter (is_var_con con . firstPat) qs)
368 new_wilds = [WildPat (hsPatType arg_pat) | arg_pat <- con_pats]
369 shift_var (EqnInfo n ctx (ConPatOut _ (PrefixCon ps') _ _ _:ps) result) =
370 EqnInfo n ctx (map unLoc ps'++ps) result
371 shift_var (EqnInfo n ctx (WildPat _ :ps) result) =
372 EqnInfo n ctx (new_wilds ++ ps) result
373 shift_var _ = panic "Check.Shift_var:No done"
375 make_row_vars :: [HsLit] -> EquationInfo -> ExhaustivePat
376 make_row_vars used_lits (EqnInfo _ _ pats _ ) =
377 (nlVarPat new_var:takeList (tail pats) (repeat nlWildPat),[(new_var,used_lits)])
378 where new_var = hash_x
380 hash_x = mkInternalName unboundKey {- doesn't matter much -}
381 (mkVarOcc FSLIT("#x"))
384 make_row_vars_for_constructor :: EquationInfo -> [WarningPat]
385 make_row_vars_for_constructor (EqnInfo _ _ pats _ ) = takeList (tail pats) (repeat nlWildPat)
387 compare_cons :: Pat Id -> Pat Id -> Bool
388 compare_cons (ConPatOut id1 _ _ _ _) (ConPatOut id2 _ _ _ _) = id1 == id2
390 remove_dups :: [Pat Id] -> [Pat Id]
392 remove_dups (x:xs) | or (map (\y -> compare_cons x y) xs) = remove_dups xs
393 | otherwise = x : remove_dups xs
395 get_used_cons :: [EquationInfo] -> [Pat Id]
396 get_used_cons qs = remove_dups [con | (EqnInfo _ _ (con@(ConPatOut _ _ _ _ _):_) _) <- qs ]
398 remove_dups' :: [HsLit] -> [HsLit]
400 remove_dups' (x:xs) | x `elem` xs = remove_dups' xs
401 | otherwise = x : remove_dups' xs
404 get_used_lits :: [EquationInfo] -> [HsLit]
405 get_used_lits qs = remove_dups' all_literals
407 all_literals = get_used_lits' qs
409 get_used_lits' :: [EquationInfo] -> [HsLit]
410 get_used_lits' [] = []
411 get_used_lits' ((EqnInfo _ _ ((LitPat lit):_) _):qs) =
412 lit : get_used_lits qs
413 get_used_lits' ((EqnInfo _ _ ((NPatOut lit _ _):_) _):qs) =
414 lit : get_used_lits qs
415 get_used_lits' (q:qs) =
418 get_unused_cons :: [Pat Id] -> [DataCon]
419 get_unused_cons used_cons = unused_cons
421 (ConPatOut _ _ ty _ _) = head used_cons
422 ty_con = tcTyConAppTyCon ty -- Newtype observable
423 all_cons = tyConDataCons ty_con
424 used_cons_as_id = map (\ (ConPatOut d _ _ _ _) -> d) used_cons
425 unused_cons = uniqSetToList
426 (mkUniqSet all_cons `minusUniqSet` mkUniqSet used_cons_as_id)
428 all_vars :: [Pat Id] -> Bool
430 all_vars (WildPat _:ps) = all_vars ps
433 remove_var :: EquationInfo -> EquationInfo
434 remove_var (EqnInfo n ctx (WildPat _:ps) result) = EqnInfo n ctx ps result
436 panic "Check.remove_var: equation does not begin with a variable"
438 -----------------------
439 eqnPats :: EquationInfo -> [Pat Id]
440 eqnPats (EqnInfo _ _ ps _) = ps
442 firstPat :: EquationInfo -> Pat Id
443 firstPat eqn_info = head (eqnPats eqn_info)
445 okGroup :: [EquationInfo] -> Bool
446 -- True if all equations have at least one pattern, and
447 -- all have the same number of patterns
449 okGroup (e:es) = n_pats > 0 && and [length (eqnPats e) == n_pats | e <- es]
451 n_pats = length (eqnPats e)
454 pprGroup es = vcat (map pprEqnInfo es)
455 pprEqnInfo e = ppr (eqnPats e)
457 is_con :: Pat Id -> Bool
458 is_con (ConPatOut _ _ _ _ _) = True
461 is_lit :: Pat Id -> Bool
462 is_lit (LitPat _) = True
463 is_lit (NPatOut _ _ _) = True
466 is_npat :: Pat Id -> Bool
467 is_npat (NPatOut _ _ _) = True
470 is_nplusk :: Pat Id -> Bool
471 is_nplusk (NPlusKPatOut _ _ _ _) = True
474 is_var :: Pat Id -> Bool
475 is_var (WildPat _) = True
478 is_var_con :: DataCon -> Pat Id -> Bool
479 is_var_con con (WildPat _) = True
480 is_var_con con (ConPatOut id _ _ _ _) | id == con = True
481 is_var_con con _ = False
483 is_var_lit :: HsLit -> Pat Id -> Bool
484 is_var_lit lit (WildPat _) = True
485 is_var_lit lit (LitPat lit') | lit == lit' = True
486 is_var_lit lit (NPatOut lit' _ _) | lit == lit' = True
487 is_var_lit lit _ = False
490 The difference beteewn @make_con@ and @make_whole_con@ is that
491 @make_wole_con@ creates a new constructor with all their arguments, and
492 @make_con@ takes a list of argumntes, creates the contructor getting their
493 arguments from the list. See where \fbox{\ ???\ } are used for details.
495 We need to reconstruct the patterns (make the constructors infix and
496 similar) at the same time that we create the constructors.
498 You can tell tuple constructors using
502 You can see if one constructor is infix with this clearer code :-))))))))))
504 Lex.isLexConSym (Name.occNameString (Name.getOccName con))
507 Rather clumsy but it works. (Simon Peyton Jones)
510 We don't mind the @nilDataCon@ because it doesn't change the way to
511 print the messsage, we are searching only for things like: @[1,2,3]@,
514 In @reconstruct_pat@ we want to ``undo'' the work
515 that we have done in @simplify_pat@.
518 @((,) x y)@ & returns to be & @(x, y)@
519 \\ @((:) x xs)@ & returns to be & @(x:xs)@
520 \\ @(x:(...:[])@ & returns to be & @[x,...]@
523 The difficult case is the third one becouse we need to follow all the
524 contructors until the @[]@ to know that we need to use the second case,
525 not the second. \fbox{\ ???\ }
528 isInfixCon con = isDataSymOcc (getOccName con)
530 is_nil (ConPatIn con (PrefixCon [])) = unLoc con == getName nilDataCon
533 is_list (ListPat _ _) = True
536 return_list id q = id == consDataCon && (is_nil q || is_list q)
538 make_list p q | is_nil q = ListPat [p] placeHolderType
539 make_list p (ListPat ps ty) = ListPat (p:ps) ty
540 make_list _ _ = panic "Check.make_list: Invalid argument"
542 make_con :: Pat Id -> ExhaustivePat -> ExhaustivePat
543 make_con (ConPatOut id _ _ _ _) (lp:lq:ps, constraints)
544 | return_list id q = (noLoc (make_list lp q) : ps, constraints)
545 | isInfixCon id = (nlInfixConPat (getName id) lp lq : ps, constraints)
549 make_con (ConPatOut id (PrefixCon pats) _ _ _) (ps, constraints)
550 | isTupleTyCon tc = (noLoc (TuplePat pats_con (tupleTyConBoxity tc)) : rest_pats, constraints)
551 | isPArrFakeCon id = (noLoc (PArrPat pats_con placeHolderType) : rest_pats, constraints)
552 | otherwise = (nlConPat name pats_con : rest_pats, constraints)
555 (pats_con, rest_pats) = splitAtList pats ps
558 -- reconstruct parallel array pattern
560 -- * don't check for the type only; we need to make sure that we are really
561 -- dealing with one of the fake constructors and not with the real
564 make_whole_con :: DataCon -> WarningPat
565 make_whole_con con | isInfixCon con = nlInfixConPat name nlWildPat nlWildPat
566 | otherwise = nlConPat name pats
569 pats = [nlWildPat | t <- dataConOrigArgTys con]
572 This equation makes the same thing as @tidy@ in @Match.lhs@, the
573 difference is that here we can do all the tidy in one place and in the
574 @Match@ tidy it must be done one column each time due to bookkeeping
579 simplify_eqns :: [EquationInfo] -> [EquationInfo]
580 simplify_eqns [] = []
581 simplify_eqns ((EqnInfo n ctx pats result):qs) =
582 (EqnInfo n ctx pats' result) : simplify_eqns qs
584 pats' = map simplify_pat pats
586 simplify_lpat :: LPat Id -> LPat Id
587 simplify_lpat p = fmap simplify_pat p
589 simplify_pat :: Pat Id -> Pat Id
590 simplify_pat pat@(WildPat gt) = pat
591 simplify_pat (VarPat id) = WildPat (idType id)
593 simplify_pat (ParPat p) = unLoc (simplify_lpat p)
594 simplify_pat (LazyPat p) = unLoc (simplify_lpat p)
595 simplify_pat (AsPat id p) = unLoc (simplify_lpat p)
596 simplify_pat (SigPatOut p ty fn) = unLoc (simplify_lpat p) -- I'm not sure this is right
598 simplify_pat (ConPatOut id ps ty tvs dicts) = ConPatOut id (simplify_con id ps) ty tvs dicts
600 simplify_pat (ListPat ps ty) =
601 unLoc $ foldr (\ x y -> mkPrefixConPat consDataCon [x,y] list_ty)
603 (map simplify_lpat ps)
604 where list_ty = mkListTy ty
606 -- introduce fake parallel array constructors to be able to handle parallel
607 -- arrays with the existing machinery for constructor pattern
609 simplify_pat (PArrPat ps ty)
610 = ConPatOut (parrFakeCon arity)
611 (PrefixCon (map simplify_lpat ps))
616 simplify_pat (TuplePat ps boxity)
617 = ConPatOut (tupleCon boxity arity)
618 (PrefixCon (map simplify_lpat ps))
619 (mkTupleTy boxity arity (map hsPatType ps)) [] []
623 simplify_pat pat@(LitPat lit) = unLoc (tidyLitPat lit (noLoc pat))
625 -- unpack string patterns fully, so we can see when they overlap with
626 -- each other, or even explicit lists of Chars.
627 simplify_pat pat@(NPatOut (HsString s) _ _) =
628 foldr (\c pat -> ConPatOut consDataCon (PrefixCon [mk_char_lit c,noLoc pat]) stringTy [] [])
629 (ConPatOut nilDataCon (PrefixCon []) stringTy [] []) (unpackFS s)
631 mk_char_lit c = noLoc $
632 ConPatOut charDataCon (PrefixCon [nlLitPat (HsCharPrim c)])
635 simplify_pat pat@(NPatOut lit lit_ty hsexpr) = unLoc (tidyNPat lit lit_ty (noLoc pat))
637 simplify_pat (NPlusKPatOut id hslit hsexpr1 hsexpr2)
638 = WildPat (idType (unLoc id))
640 simplify_pat (DictPat dicts methods)
641 = case num_of_d_and_ms of
642 0 -> simplify_pat (TuplePat [] Boxed)
643 1 -> simplify_pat (head dict_and_method_pats)
644 _ -> simplify_pat (TuplePat (map noLoc dict_and_method_pats) Boxed)
646 num_of_d_and_ms = length dicts + length methods
647 dict_and_method_pats = map VarPat (dicts ++ methods)
650 simplify_con con (PrefixCon ps) = PrefixCon (map simplify_lpat ps)
651 simplify_con con (InfixCon p1 p2) = PrefixCon [simplify_lpat p1, simplify_lpat p2]
652 simplify_con con (RecCon fs)
653 | null fs = PrefixCon [nlWildPat | t <- dataConOrigArgTys con]
654 -- Special case for null patterns; maybe not a record at all
655 | otherwise = PrefixCon (map (simplify_lpat.snd) all_pats)
657 -- pad out all the missing fields with WildPats.
658 field_pats = map (\ f -> (getName f, nlWildPat))
659 (dataConFieldLabels con)
660 all_pats = foldr (\ (id,p) acc -> insertNm (getName (unLoc id)) p acc)
663 insertNm nm p [] = [(nm,p)]
664 insertNm nm p (x@(n,_):xs)
665 | nm == n = (nm,p):xs
666 | otherwise = x : insertNm nm p xs