2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[PatSyntax]{Abstract Haskell syntax---patterns}
8 {-# OPTIONS -fno-warn-incomplete-patterns #-}
9 -- The above warning supression flag is a temporary kludge.
10 -- While working on this module you are encouraged to remove it and fix
11 -- any warnings in the module. See
12 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 Pat(..), InPat, OutPat, LPat,
19 HsConPatDetails, hsConPatArgs,
20 HsRecFields(..), HsRecField(..), hsRecFields,
24 mkPrefixConPat, mkCharLitPat, mkNilPat, mkCoPat, mkCoPatCoI,
27 patsAreAllCons, isConPat, isSigPat, isWildPat,
28 patsAreAllLits, isLitPat, isIrrefutableHsPat
31 import {-# SOURCE #-} HsExpr (SyntaxExpr, LHsExpr, pprLExpr)
40 import PprCore ( {- instance OutputableBndr TyVar -} )
53 type InPat id = LPat id -- No 'Out' constructors
54 type OutPat id = LPat id -- No 'In' constructors
56 type LPat id = Located (Pat id)
59 = ------------ Simple patterns ---------------
60 WildPat PostTcType -- Wild card
61 -- The sole reason for a type on a WildPat is to
62 -- support hsPatType :: Pat Id -> Type
64 | VarPat id -- Variable
65 | VarPatOut id (DictBinds id) -- Used only for overloaded Ids; the
66 -- bindings give its overloaded instances
67 | LazyPat (LPat id) -- Lazy pattern
68 | AsPat (Located id) (LPat id) -- As pattern
69 | ParPat (LPat id) -- Parenthesised pattern
70 | BangPat (LPat id) -- Bang pattern
72 ------------ Lists, tuples, arrays ---------------
73 | ListPat [LPat id] -- Syntactic list
74 PostTcType -- The type of the elements
76 | TuplePat [LPat id] -- Tuple
77 Boxity -- UnitPat is TuplePat []
79 -- You might think that the PostTcType was redundant, but it's essential
82 -- f :: (T a, a) -> Int
84 -- When desugaring, we must generate
85 -- f = /\a. \v::a. case v of (t::T a, w::a) ->
86 -- case t of (T1 (x::Int)) ->
87 -- Note the (w::a), NOT (w::Int), because we have not yet
88 -- refined 'a' to Int. So we must know that the second component
89 -- of the tuple is of type 'a' not Int. See selectMatchVar
91 | PArrPat [LPat id] -- Syntactic parallel array
92 PostTcType -- The type of the elements
94 ------------ Constructor patterns ---------------
95 | ConPatIn (Located id)
99 pat_con :: Located DataCon,
100 pat_tvs :: [TyVar], -- Existentially bound type variables (tyvars only)
101 pat_dicts :: [id], -- Ditto *coercion variables* and *dictionaries*
102 -- One reason for putting coercion variable here, I think,
103 -- is to ensure their kinds are zonked
104 pat_binds :: DictBinds id, -- Bindings involving those dictionaries
105 pat_args :: HsConPatDetails id,
106 pat_ty :: Type -- The type of the pattern
109 ------------ View patterns ---------------
110 | ViewPat (LHsExpr id)
112 PostTcType -- The overall type of the pattern
113 -- (= the argument type of the view function)
116 ------------ Quasiquoted patterns ---------------
117 -- See Note [Quasi-quote overview] in TcSplice
118 | QuasiQuotePat (HsQuasiQuote id)
120 ------------ Literal and n+k patterns ---------------
121 | LitPat HsLit -- Used for *non-overloaded* literal patterns:
122 -- Int#, Char#, Int, Char, String, etc.
124 | NPat (HsOverLit id) -- ALWAYS positive
125 (Maybe (SyntaxExpr id)) -- Just (Name of 'negate') for negative
126 -- patterns, Nothing otherwise
127 (SyntaxExpr id) -- Equality checker, of type t->t->Bool
129 | NPlusKPat (Located id) -- n+k pattern
130 (HsOverLit id) -- It'll always be an HsIntegral
131 (SyntaxExpr id) -- (>=) function, of type t->t->Bool
132 (SyntaxExpr id) -- Name of '-' (see RnEnv.lookupSyntaxName)
134 ------------ Generics ---------------
135 | TypePat (LHsType id) -- Type pattern for generic definitions
136 -- e.g f{| a+b |} = ...
137 -- These show up only in class declarations,
138 -- and should be a top-level pattern
140 ------------ Pattern type signatures ---------------
141 | SigPatIn (LPat id) -- Pattern with a type signature
144 | SigPatOut (LPat id) -- Pattern with a type signature
147 ------------ Pattern coercions (translation only) ---------------
148 | CoPat HsWrapper -- If co::t1 -> t2, p::t2,
149 -- then (CoPat co p) :: t1
150 (Pat id) -- Why not LPat? Ans: existing locn will do
151 Type -- Type of whole pattern, t1
152 -- During desugaring a (CoPat co pat) turns into a cast with 'co' on
153 -- the scrutinee, followed by a match on 'pat'
156 HsConDetails is use for patterns/expressions *and* for data type declarations
159 data HsConDetails arg rec
160 = PrefixCon [arg] -- C p1 p2 p3
161 | RecCon rec -- C { x = p1, y = p2 }
162 | InfixCon arg arg -- p1 `C` p2
164 type HsConPatDetails id = HsConDetails (LPat id) (HsRecFields id (LPat id))
166 hsConPatArgs :: HsConPatDetails id -> [LPat id]
167 hsConPatArgs (PrefixCon ps) = ps
168 hsConPatArgs (RecCon fs) = map hsRecFieldArg (rec_flds fs)
169 hsConPatArgs (InfixCon p1 p2) = [p1,p2]
172 However HsRecFields is used only for patterns and expressions
173 (not data type declarations)
176 data HsRecFields id arg -- A bunch of record fields
177 -- { x = 3, y = True }
178 -- Used for both expressiona and patterns
179 = HsRecFields { rec_flds :: [HsRecField id arg],
180 rec_dotdot :: Maybe Int }
181 -- Nothing => the normal case
182 -- Just n => the group uses ".." notation,
183 -- and the first n elts of rec_flds
184 -- were the user-written ones
185 -- (In the latter case, the remaining elts of
186 -- rec_flds are the non-user-written ones)
188 data HsRecField id arg = HsRecField {
189 hsRecFieldId :: Located id,
190 hsRecFieldArg :: arg,
191 hsRecPun :: Bool -- Note [Punning]
196 -- If you write T { x, y = v+1 }, the HsRecFields will be
197 -- HsRecField x x True ...
198 -- HsRecField y (v+1) False ...
199 -- That is, for "punned" field x is immediately expanded to x=x
200 -- but with a punning flag so we can detect it later
201 -- (e.g. when pretty printing)
203 hsRecFields :: HsRecFields id arg -> [id]
204 hsRecFields rbinds = map (unLoc . hsRecFieldId) (rec_flds rbinds)
208 data HsQuasiQuote id = HsQuasiQuote
216 %************************************************************************
220 %************************************************************************
223 instance (OutputableBndr name) => Outputable (Pat name) where
226 pprPatBndr :: OutputableBndr name => name -> SDoc
227 pprPatBndr var -- Print with type info if -dppr-debug is on
228 = getPprStyle $ \ sty ->
229 if debugStyle sty then
230 parens (pprBndr LambdaBind var) -- Could pass the site to pprPat
231 -- but is it worth it?
235 pprPat :: (OutputableBndr name) => Pat name -> SDoc
236 pprPat (VarPat var) = pprPatBndr var
237 pprPat (VarPatOut var bs) = parens (pprPatBndr var <+> braces (ppr bs))
238 pprPat (WildPat _) = char '_'
239 pprPat (LazyPat pat) = char '~' <> ppr pat
240 pprPat (BangPat pat) = char '!' <> ppr pat
241 pprPat (AsPat name pat) = parens (hcat [ppr name, char '@', ppr pat])
242 pprPat (ViewPat expr pat _) = parens (hcat [pprLExpr expr, text " -> ", ppr pat])
243 pprPat (ParPat pat) = parens (ppr pat)
244 pprPat (ListPat pats _) = brackets (interpp'SP pats)
245 pprPat (PArrPat pats _) = pabrackets (interpp'SP pats)
246 pprPat (TuplePat pats bx _) = tupleParens bx (interpp'SP pats)
248 pprPat (ConPatIn con details) = pprUserCon con details
249 pprPat (ConPatOut { pat_con = con, pat_tvs = tvs, pat_dicts = dicts,
250 pat_binds = binds, pat_args = details })
251 = getPprStyle $ \ sty -> -- Tiresome; in TcBinds.tcRhs we print out a
252 if debugStyle sty then -- typechecked Pat in an error message,
253 -- and we want to make sure it prints nicely
254 ppr con <+> sep [ hsep (map pprPatBndr tvs) <+> hsep (map pprPatBndr dicts),
255 pprLHsBinds binds, pprConArgs details]
256 else pprUserCon con details
258 pprPat (LitPat s) = ppr s
259 pprPat (NPat l Nothing _) = ppr l
260 pprPat (NPat l (Just _) _) = char '-' <> ppr l
261 pprPat (NPlusKPat n k _ _) = hcat [ppr n, char '+', ppr k]
262 pprPat (QuasiQuotePat (HsQuasiQuote name quoter _ quote))
263 = char '$' <> brackets (ppr name) <>
264 ptext (sLit "[:") <> ppr quoter <> ptext (sLit "|") <>
265 ppr quote <> ptext (sLit "|]")
266 pprPat (TypePat ty) = ptext (sLit "{|") <> ppr ty <> ptext (sLit "|}")
267 pprPat (CoPat co pat _) = parens (pprHsWrapper (ppr pat) co)
268 pprPat (SigPatIn pat ty) = ppr pat <+> dcolon <+> ppr ty
269 pprPat (SigPatOut pat ty) = ppr pat <+> dcolon <+> ppr ty
271 pprUserCon :: (Outputable con, OutputableBndr id) => con -> HsConPatDetails id -> SDoc
272 pprUserCon c (InfixCon p1 p2) = ppr p1 <+> ppr c <+> ppr p2
273 pprUserCon c details = ppr c <+> pprConArgs details
275 pprConArgs :: OutputableBndr id => HsConPatDetails id -> SDoc
276 pprConArgs (PrefixCon pats) = interppSP pats
277 pprConArgs (InfixCon p1 p2) = interppSP [p1,p2]
278 pprConArgs (RecCon rpats) = ppr rpats
280 instance (OutputableBndr id, Outputable arg)
281 => Outputable (HsRecFields id arg) where
282 ppr (HsRecFields { rec_flds = flds, rec_dotdot = Nothing })
283 = braces (fsep (punctuate comma (map ppr flds)))
284 ppr (HsRecFields { rec_flds = flds, rec_dotdot = Just n })
285 = braces (fsep (punctuate comma (map ppr (take n flds) ++ [dotdot])))
287 dotdot = ptext (sLit "..") <+> ifPprDebug (ppr (drop n flds))
289 instance (OutputableBndr id, Outputable arg)
290 => Outputable (HsRecField id arg) where
291 ppr (HsRecField { hsRecFieldId = f, hsRecFieldArg = arg,
293 = ppr f <+> (if pun then empty else equals <+> ppr arg)
295 -- add parallel array brackets around a document
297 pabrackets :: SDoc -> SDoc
298 pabrackets p = ptext (sLit "[:") <> p <> ptext (sLit ":]")
302 %************************************************************************
306 %************************************************************************
309 mkPrefixConPat :: DataCon -> [OutPat id] -> Type -> OutPat id
310 -- Make a vanilla Prefix constructor pattern
311 mkPrefixConPat dc pats ty
312 = noLoc $ ConPatOut { pat_con = noLoc dc, pat_tvs = [], pat_dicts = [],
313 pat_binds = emptyLHsBinds, pat_args = PrefixCon pats,
316 mkNilPat :: Type -> OutPat id
317 mkNilPat ty = mkPrefixConPat nilDataCon [] ty
319 mkCharLitPat :: Char -> OutPat id
320 mkCharLitPat c = mkPrefixConPat charDataCon [noLoc $ LitPat (HsCharPrim c)] charTy
322 mkCoPat :: HsWrapper -> Pat id -> Type -> Pat id
324 | isIdHsWrapper co = pat
325 | otherwise = CoPat co pat ty
327 mkCoPatCoI :: CoercionI -> Pat id -> Type -> Pat id
328 mkCoPatCoI IdCo pat _ = pat
329 mkCoPatCoI (ACo co) pat ty = mkCoPat (WpCast co) pat ty
333 %************************************************************************
335 %* Predicates for checking things about pattern-lists in EquationInfo *
337 %************************************************************************
339 \subsection[Pat-list-predicates]{Look for interesting things in patterns}
341 Unlike in the Wadler chapter, where patterns are either ``variables''
342 or ``constructors,'' here we distinguish between:
345 Patterns that cannot fail to match: variables, wildcards, and lazy
348 These are the irrefutable patterns; the two other categories
349 are refutable patterns.
352 A non-literal constructor pattern (see next category).
354 \item[literal patterns:]
355 At least the numeric ones may be overloaded.
358 A pattern is in {\em exactly one} of the above three categories; `as'
359 patterns are treated specially, of course.
361 The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
363 isWildPat :: Pat id -> Bool
364 isWildPat (WildPat _) = True
367 patsAreAllCons :: [Pat id] -> Bool
368 patsAreAllCons pat_list = all isConPat pat_list
370 isConPat :: Pat id -> Bool
371 isConPat (AsPat _ pat) = isConPat (unLoc pat)
372 isConPat (ConPatIn {}) = True
373 isConPat (ConPatOut {}) = True
374 isConPat (ListPat {}) = True
375 isConPat (PArrPat {}) = True
376 isConPat (TuplePat {}) = True
379 isSigPat :: Pat id -> Bool
380 isSigPat (SigPatIn _ _) = True
381 isSigPat (SigPatOut _ _) = True
384 patsAreAllLits :: [Pat id] -> Bool
385 patsAreAllLits pat_list = all isLitPat pat_list
387 isLitPat :: Pat id -> Bool
388 isLitPat (AsPat _ pat) = isLitPat (unLoc pat)
389 isLitPat (LitPat _) = True
390 isLitPat (NPat _ _ _) = True
391 isLitPat (NPlusKPat _ _ _ _) = True
394 isBangHsBind :: HsBind id -> Bool
395 -- In this module because HsPat is above HsBinds in the import graph
396 isBangHsBind (PatBind { pat_lhs = L _ (BangPat _) }) = True
397 isBangHsBind _ = False
399 isIrrefutableHsPat :: OutputableBndr id => LPat id -> Bool
400 -- (isIrrefutableHsPat p) is true if matching against p cannot fail,
401 -- in the sense of falling through to the next pattern.
402 -- (NB: this is not quite the same as the (silly) defn
403 -- in 3.17.2 of the Haskell 98 report.)
405 -- isIrrefutableHsPat returns False if it's in doubt; specifically
406 -- on a ConPatIn it doesn't know the size of the constructor family
407 -- But if it returns True, the pattern is definitely irrefutable
408 isIrrefutableHsPat pat
411 go (L _ pat) = go1 pat
413 go1 (WildPat _) = True
414 go1 (VarPat _) = True
415 go1 (VarPatOut _ _) = True
416 go1 (LazyPat _) = True
417 go1 (BangPat pat) = go pat
418 go1 (CoPat _ pat _) = go1 pat
419 go1 (ParPat pat) = go pat
420 go1 (AsPat _ pat) = go pat
421 go1 (ViewPat _ pat _) = go pat
422 go1 (SigPatIn pat _) = go pat
423 go1 (SigPatOut pat _) = go pat
424 go1 (TuplePat pats _ _) = all go pats
425 go1 (ListPat _ _) = False
426 go1 (PArrPat _ _) = False -- ?
428 go1 (ConPatIn _ _) = False -- Conservative
429 go1 (ConPatOut{ pat_con = L _ con, pat_args = details })
430 = isProductTyCon (dataConTyCon con)
431 && all go (hsConPatArgs details)
433 go1 (LitPat _) = False
434 go1 (NPat _ _ _) = False
435 go1 (NPlusKPat _ _ _ _) = False
437 go1 (QuasiQuotePat {}) = urk pat -- Gotten rid of by renamer, before
438 -- isIrrefutablePat is called
439 go1 (TypePat {}) = urk pat
441 urk pat = pprPanic "isIrrefutableHsPat:" (ppr pat)