2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[PatSyntax]{Abstract Haskell syntax---patterns}
9 Pat(..), InPat, OutPat, LPat,
11 HsConDetails(..), hsConArgs,
12 HsRecField(..), mkRecField,
14 mkPrefixConPat, mkCharLitPat, mkNilPat, mkCoPat,
17 patsAreAllCons, isConPat, isSigPat, isWildPat,
18 patsAreAllLits, isLitPat, isIrrefutableHsPat
21 #include "HsVersions.h"
24 import {-# SOURCE #-} HsExpr ( SyntaxExpr )
33 import PprCore ( {- instance OutputableBndr TyVar -} )
45 type InPat id = LPat id -- No 'Out' constructors
46 type OutPat id = LPat id -- No 'In' constructors
48 type LPat id = Located (Pat id)
51 = ------------ Simple patterns ---------------
52 WildPat PostTcType -- Wild card
53 | VarPat id -- Variable
54 | VarPatOut id (DictBinds id) -- Used only for overloaded Ids; the
55 -- bindings give its overloaded instances
56 | LazyPat (LPat id) -- Lazy pattern
57 | AsPat (Located id) (LPat id) -- As pattern
58 | ParPat (LPat id) -- Parenthesised pattern
59 | BangPat (LPat id) -- Bang patterng
61 ------------ Lists, tuples, arrays ---------------
62 | ListPat [LPat id] -- Syntactic list
63 PostTcType -- The type of the elements
65 | TuplePat [LPat id] -- Tuple
66 Boxity -- UnitPat is TuplePat []
68 -- You might think that the PostTcType was redundant, but it's essential
71 -- f :: (T a, a) -> Int
73 -- When desugaring, we must generate
74 -- f = /\a. \v::a. case v of (t::T a, w::a) ->
75 -- case t of (T1 (x::Int)) ->
76 -- Note the (w::a), NOT (w::Int), because we have not yet
77 -- refined 'a' to Int. So we must know that the second component
78 -- of the tuple is of type 'a' not Int. See selectMatchVar
80 | PArrPat [LPat id] -- Syntactic parallel array
81 PostTcType -- The type of the elements
83 ------------ Constructor patterns ---------------
84 | ConPatIn (Located id)
85 (HsConDetails id (LPat id))
88 pat_con :: Located DataCon,
89 pat_tvs :: [TyVar], -- Existentially bound type variables
90 -- including any bound coercion variables
91 pat_dicts :: [id], -- Ditto dictionaries
92 pat_binds :: DictBinds id, -- Bindings involving those dictionaries
93 pat_args :: HsConDetails id (LPat id),
94 pat_ty :: Type -- The type of the pattern
97 ------------ Literal and n+k patterns ---------------
98 | LitPat HsLit -- Used for *non-overloaded* literal patterns:
99 -- Int#, Char#, Int, Char, String, etc.
101 | NPat (HsOverLit id) -- ALWAYS positive
102 (Maybe (SyntaxExpr id)) -- Just (Name of 'negate') for negative
103 -- patterns, Nothing otherwise
104 (SyntaxExpr id) -- Equality checker, of type t->t->Bool
105 PostTcType -- Type of the pattern
107 | NPlusKPat (Located id) -- n+k pattern
108 (HsOverLit id) -- It'll always be an HsIntegral
109 (SyntaxExpr id) -- (>=) function, of type t->t->Bool
110 (SyntaxExpr id) -- Name of '-' (see RnEnv.lookupSyntaxName)
112 ------------ Generics ---------------
113 | TypePat (LHsType id) -- Type pattern for generic definitions
114 -- e.g f{| a+b |} = ...
115 -- These show up only in class declarations,
116 -- and should be a top-level pattern
118 ------------ Pattern type signatures ---------------
119 | SigPatIn (LPat id) -- Pattern with a type signature
122 | SigPatOut (LPat id) -- Pattern with a type signature
125 ------------ Dictionary patterns (translation only) ---------------
126 | DictPat -- Used when destructing Dictionaries with an explicit case
127 [id] -- Superclass dicts
130 ------------ Pattern coercions (translation only) ---------------
131 | CoPat HsWrapper -- If co::t1 -> t2, p::t2,
132 -- then (CoPat co p) :: t1
133 (Pat id) -- Why not LPat? Ans: existing locn will do
135 -- During desugaring a (CoPat co pat) turns into a cast with 'co' on
136 -- the scrutinee, followed by a match on 'pat'
139 HsConDetails is use both for patterns and for data type declarations
142 data HsConDetails id arg
143 = PrefixCon [arg] -- C p1 p2 p3
144 | RecCon [HsRecField id arg] -- C { x = p1, y = p2 }
145 | InfixCon arg arg -- p1 `C` p2
147 data HsRecField id arg = HsRecField {
148 hsRecFieldId :: Located id,
149 hsRecFieldArg :: arg,
150 hsRecFieldDoc :: Maybe (LHsDoc id)
153 mkRecField id arg = HsRecField id arg Nothing
155 hsConArgs :: HsConDetails id arg -> [arg]
156 hsConArgs (PrefixCon ps) = ps
157 hsConArgs (RecCon fs) = map hsRecFieldArg fs
158 hsConArgs (InfixCon p1 p2) = [p1,p2]
162 %************************************************************************
166 %************************************************************************
169 instance (OutputableBndr name) => Outputable (Pat name) where
172 pprPatBndr :: OutputableBndr name => name -> SDoc
173 pprPatBndr var -- Print with type info if -dppr-debug is on
174 = getPprStyle $ \ sty ->
175 if debugStyle sty then
176 parens (pprBndr LambdaBind var) -- Could pass the site to pprPat
177 -- but is it worth it?
181 pprPat :: (OutputableBndr name) => Pat name -> SDoc
182 pprPat (VarPat var) = pprPatBndr var
183 pprPat (VarPatOut var bs) = parens (pprPatBndr var <+> braces (ppr bs))
184 pprPat (WildPat _) = char '_'
185 pprPat (LazyPat pat) = char '~' <> ppr pat
186 pprPat (BangPat pat) = char '!' <> ppr pat
187 pprPat (AsPat name pat) = parens (hcat [ppr name, char '@', ppr pat])
188 pprPat (ParPat pat) = parens (ppr pat)
189 pprPat (ListPat pats _) = brackets (interpp'SP pats)
190 pprPat (PArrPat pats _) = pabrackets (interpp'SP pats)
191 pprPat (TuplePat pats bx _) = tupleParens bx (interpp'SP pats)
193 pprPat (ConPatIn con details) = pprUserCon con details
194 pprPat (ConPatOut { pat_con = con, pat_tvs = tvs, pat_dicts = dicts,
195 pat_binds = binds, pat_args = details })
196 = getPprStyle $ \ sty -> -- Tiresome; in TcBinds.tcRhs we print out a
197 if debugStyle sty then -- typechecked Pat in an error message,
198 -- and we want to make sure it prints nicely
199 ppr con <+> sep [ hsep (map pprPatBndr tvs) <+> hsep (map pprPatBndr dicts),
200 pprLHsBinds binds, pprConArgs details]
201 else pprUserCon con details
203 pprPat (LitPat s) = ppr s
204 pprPat (NPat l Nothing _ _) = ppr l
205 pprPat (NPat l (Just _) _ _) = char '-' <> ppr l
206 pprPat (NPlusKPat n k _ _) = hcat [ppr n, char '+', ppr k]
207 pprPat (TypePat ty) = ptext SLIT("{|") <> ppr ty <> ptext SLIT("|}")
208 pprPat (CoPat co pat _) = parens (pprHsWrapper (ppr pat) co)
209 pprPat (SigPatIn pat ty) = ppr pat <+> dcolon <+> ppr ty
210 pprPat (SigPatOut pat ty) = ppr pat <+> dcolon <+> ppr ty
211 pprPat (DictPat ds ms) = parens (sep [ptext SLIT("{-dict-}"),
212 brackets (interpp'SP ds),
213 brackets (interpp'SP ms)])
215 pprUserCon c (InfixCon p1 p2) = ppr p1 <+> ppr c <+> ppr p2
216 pprUserCon c details = ppr c <+> pprConArgs details
218 pprConArgs (PrefixCon pats) = interppSP pats
219 pprConArgs (InfixCon p1 p2) = interppSP [p1,p2]
220 pprConArgs (RecCon rpats) = braces (hsep (punctuate comma (map (pp_rpat) rpats)))
222 pp_rpat (HsRecField v p _d) =
223 hsep [ppr v, char '=', ppr p]
225 -- add parallel array brackets around a document
227 pabrackets :: SDoc -> SDoc
228 pabrackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
230 instance (OutputableBndr id, Outputable arg) =>
231 Outputable (HsRecField id arg) where
232 ppr (HsRecField n ty doc) = ppr n <+> dcolon <+> ppr ty <+> ppr_mbDoc doc
236 %************************************************************************
240 %************************************************************************
243 mkPrefixConPat :: DataCon -> [OutPat id] -> Type -> OutPat id
244 -- Make a vanilla Prefix constructor pattern
245 mkPrefixConPat dc pats ty
246 = noLoc $ ConPatOut { pat_con = noLoc dc, pat_tvs = [], pat_dicts = [],
247 pat_binds = emptyLHsBinds, pat_args = PrefixCon pats,
250 mkNilPat :: Type -> OutPat id
251 mkNilPat ty = mkPrefixConPat nilDataCon [] ty
253 mkCharLitPat :: Char -> OutPat id
254 mkCharLitPat c = mkPrefixConPat charDataCon [noLoc $ LitPat (HsCharPrim c)] charTy
256 mkCoPat :: HsWrapper -> OutPat id -> Type -> OutPat id
257 mkCoPat co lpat@(L loc pat) ty
258 | isIdHsWrapper co = lpat
259 | otherwise = L loc (CoPat co pat ty)
263 %************************************************************************
265 %* Predicates for checking things about pattern-lists in EquationInfo *
267 %************************************************************************
269 \subsection[Pat-list-predicates]{Look for interesting things in patterns}
271 Unlike in the Wadler chapter, where patterns are either ``variables''
272 or ``constructors,'' here we distinguish between:
275 Patterns that cannot fail to match: variables, wildcards, and lazy
278 These are the irrefutable patterns; the two other categories
279 are refutable patterns.
282 A non-literal constructor pattern (see next category).
284 \item[literal patterns:]
285 At least the numeric ones may be overloaded.
288 A pattern is in {\em exactly one} of the above three categories; `as'
289 patterns are treated specially, of course.
291 The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
293 isWildPat (WildPat _) = True
294 isWildPat other = False
296 patsAreAllCons :: [Pat id] -> Bool
297 patsAreAllCons pat_list = all isConPat pat_list
299 isConPat (AsPat _ pat) = isConPat (unLoc pat)
300 isConPat (ConPatIn {}) = True
301 isConPat (ConPatOut {}) = True
302 isConPat (ListPat {}) = True
303 isConPat (PArrPat {}) = True
304 isConPat (TuplePat {}) = True
305 isConPat (DictPat ds ms) = (length ds + length ms) > 1
306 isConPat other = False
308 isSigPat (SigPatIn _ _) = True
309 isSigPat (SigPatOut _ _) = True
310 isSigPat other = False
312 patsAreAllLits :: [Pat id] -> Bool
313 patsAreAllLits pat_list = all isLitPat pat_list
315 isLitPat (AsPat _ pat) = isLitPat (unLoc pat)
316 isLitPat (LitPat _) = True
317 isLitPat (NPat _ _ _ _) = True
318 isLitPat (NPlusKPat _ _ _ _) = True
319 isLitPat other = False
321 isBangHsBind :: HsBind id -> Bool
322 -- In this module because HsPat is above HsBinds in the import graph
323 isBangHsBind (PatBind { pat_lhs = L _ (BangPat p) }) = True
324 isBangHsBind bind = False
326 isIrrefutableHsPat :: LPat id -> Bool
327 -- This function returns False if it's in doubt; specifically
328 -- on a ConPatIn it doesn't know the size of the constructor family
329 -- But if it returns True, the pattern is definitely irrefutable
330 isIrrefutableHsPat pat
333 go (L _ pat) = go1 pat
335 go1 (WildPat _) = True
336 go1 (VarPat _) = True
337 go1 (VarPatOut _ _) = True
338 go1 (LazyPat pat) = True
339 go1 (BangPat pat) = go pat
340 go1 (CoPat _ pat _) = go1 pat
341 go1 (ParPat pat) = go pat
342 go1 (AsPat _ pat) = go pat
343 go1 (SigPatIn pat _) = go pat
344 go1 (SigPatOut pat _) = go pat
345 go1 (TuplePat pats _ _) = all go pats
346 go1 (ListPat pats _) = False
347 go1 (PArrPat pats _) = False -- ?
349 go1 (ConPatIn _ _) = False -- Conservative
350 go1 (ConPatOut{ pat_con = L _ con, pat_args = details })
351 = isProductTyCon (dataConTyCon con)
352 && all go (hsConArgs details)
354 go1 (LitPat _) = False
355 go1 (NPat _ _ _ _) = False
356 go1 (NPlusKPat _ _ _ _) = False
358 go1 (TypePat _) = panic "isIrrefutableHsPat: type pattern"
359 go1 (DictPat _ _) = panic "isIrrefutableHsPat: type pattern"