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 -- 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,
22 mkPrefixConPat, mkCharLitPat, mkNilPat, mkCoPat, mkCoPatCoI,
25 patsAreAllCons, isConPat, isSigPat, isWildPat,
26 patsAreAllLits, isLitPat, isIrrefutableHsPat
29 #include "HsVersions.h"
31 import {-# SOURCE #-} HsExpr (SyntaxExpr, LHsExpr, pprLExpr)
41 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
101 -- including any bound coercion variables
102 pat_dicts :: [id], -- Ditto dictionaries
103 pat_binds :: DictBinds id, -- Bindings involving those dictionaries
104 pat_args :: HsConPatDetails id,
105 pat_ty :: Type -- The type of the pattern
108 ------------ View patterns ---------------
109 | ViewPat (LHsExpr id)
111 PostTcType -- The overall type of the pattern
112 -- (= the argument type of the view function)
115 ------------ Literal and n+k patterns ---------------
116 | LitPat HsLit -- Used for *non-overloaded* literal patterns:
117 -- Int#, Char#, Int, Char, String, etc.
119 | NPat (HsOverLit id) -- ALWAYS positive
120 (Maybe (SyntaxExpr id)) -- Just (Name of 'negate') for negative
121 -- patterns, Nothing otherwise
122 (SyntaxExpr id) -- Equality checker, of type t->t->Bool
124 | NPlusKPat (Located id) -- n+k pattern
125 (HsOverLit id) -- It'll always be an HsIntegral
126 (SyntaxExpr id) -- (>=) function, of type t->t->Bool
127 (SyntaxExpr id) -- Name of '-' (see RnEnv.lookupSyntaxName)
129 ------------ Generics ---------------
130 | TypePat (LHsType id) -- Type pattern for generic definitions
131 -- e.g f{| a+b |} = ...
132 -- These show up only in class declarations,
133 -- and should be a top-level pattern
135 ------------ Pattern type signatures ---------------
136 | SigPatIn (LPat id) -- Pattern with a type signature
139 | SigPatOut (LPat id) -- Pattern with a type signature
142 ------------ Pattern coercions (translation only) ---------------
143 | CoPat HsWrapper -- If co::t1 -> t2, p::t2,
144 -- then (CoPat co p) :: t1
145 (Pat id) -- Why not LPat? Ans: existing locn will do
146 Type -- Type of whole pattern, t1
147 -- During desugaring a (CoPat co pat) turns into a cast with 'co' on
148 -- the scrutinee, followed by a match on 'pat'
151 HsConDetails is use for patterns/expressions *and* for data type declarations
154 data HsConDetails arg rec
155 = PrefixCon [arg] -- C p1 p2 p3
156 | RecCon rec -- C { x = p1, y = p2 }
157 | InfixCon arg arg -- p1 `C` p2
159 type HsConPatDetails id = HsConDetails (LPat id) (HsRecFields id (LPat id))
161 hsConPatArgs :: HsConPatDetails id -> [LPat id]
162 hsConPatArgs (PrefixCon ps) = ps
163 hsConPatArgs (RecCon fs) = map hsRecFieldArg (rec_flds fs)
164 hsConPatArgs (InfixCon p1 p2) = [p1,p2]
167 However HsRecFields is used only for patterns and expressions
168 (not data type declarations)
171 data HsRecFields id arg -- A bunch of record fields
172 -- { x = 3, y = True }
173 -- Used for both expressiona and patterns
174 = HsRecFields { rec_flds :: [HsRecField id arg],
175 rec_dotdot :: Maybe Int }
176 -- Nothing => the normal case
177 -- Just n => the group uses ".." notation,
178 -- and the first n elts of rec_flds
179 -- were the user-written ones
180 -- (In the latter case, the remaining elts of
181 -- rec_flds are the non-user-written ones)
183 data HsRecField id arg = HsRecField {
184 hsRecFieldId :: Located id,
185 hsRecFieldArg :: arg,
186 hsRecPun :: Bool -- Note [Punning]
191 -- If you write T { x, y = v+1 }, the HsRecFields will be
192 -- HsRecField x x True ...
193 -- HsRecField y (v+1) False ...
194 -- That is, for "punned" field x is immediately expanded to x=x
195 -- but with a punning flag so we can detect it later
196 -- (e.g. when pretty printing)
198 hsRecFields :: HsRecFields id arg -> [id]
199 hsRecFields rbinds = map (unLoc . hsRecFieldId) (rec_flds rbinds)
203 %************************************************************************
207 %************************************************************************
210 instance (OutputableBndr name) => Outputable (Pat name) where
213 pprPatBndr :: OutputableBndr name => name -> SDoc
214 pprPatBndr var -- Print with type info if -dppr-debug is on
215 = getPprStyle $ \ sty ->
216 if debugStyle sty then
217 parens (pprBndr LambdaBind var) -- Could pass the site to pprPat
218 -- but is it worth it?
222 pprPat :: (OutputableBndr name) => Pat name -> SDoc
223 pprPat (VarPat var) = pprPatBndr var
224 pprPat (VarPatOut var bs) = parens (pprPatBndr var <+> braces (ppr bs))
225 pprPat (WildPat _) = char '_'
226 pprPat (LazyPat pat) = char '~' <> ppr pat
227 pprPat (BangPat pat) = char '!' <> ppr pat
228 pprPat (AsPat name pat) = parens (hcat [ppr name, char '@', ppr pat])
229 pprPat (ViewPat expr pat _) = parens (hcat [pprLExpr expr, text " -> ", ppr pat])
230 pprPat (ParPat pat) = parens (ppr pat)
231 pprPat (ListPat pats _) = brackets (interpp'SP pats)
232 pprPat (PArrPat pats _) = pabrackets (interpp'SP pats)
233 pprPat (TuplePat pats bx _) = tupleParens bx (interpp'SP pats)
235 pprPat (ConPatIn con details) = pprUserCon con details
236 pprPat (ConPatOut { pat_con = con, pat_tvs = tvs, pat_dicts = dicts,
237 pat_binds = binds, pat_args = details })
238 = getPprStyle $ \ sty -> -- Tiresome; in TcBinds.tcRhs we print out a
239 if debugStyle sty then -- typechecked Pat in an error message,
240 -- and we want to make sure it prints nicely
241 ppr con <+> sep [ hsep (map pprPatBndr tvs) <+> hsep (map pprPatBndr dicts),
242 pprLHsBinds binds, pprConArgs details]
243 else pprUserCon con details
245 pprPat (LitPat s) = ppr s
246 pprPat (NPat l Nothing _) = ppr l
247 pprPat (NPat l (Just _) _) = char '-' <> ppr l
248 pprPat (NPlusKPat n k _ _) = hcat [ppr n, char '+', ppr k]
249 pprPat (TypePat ty) = ptext SLIT("{|") <> ppr ty <> ptext SLIT("|}")
250 pprPat (CoPat co pat _) = parens (pprHsWrapper (ppr pat) co)
251 pprPat (SigPatIn pat ty) = ppr pat <+> dcolon <+> ppr ty
252 pprPat (SigPatOut pat ty) = ppr pat <+> dcolon <+> ppr ty
254 pprUserCon c (InfixCon p1 p2) = ppr p1 <+> ppr c <+> ppr p2
255 pprUserCon c details = ppr c <+> pprConArgs details
257 pprConArgs (PrefixCon pats) = interppSP pats
258 pprConArgs (InfixCon p1 p2) = interppSP [p1,p2]
259 pprConArgs (RecCon rpats) = ppr rpats
261 instance (OutputableBndr id, Outputable arg)
262 => Outputable (HsRecFields id arg) where
263 ppr (HsRecFields { rec_flds = flds, rec_dotdot = Nothing })
264 = braces (fsep (punctuate comma (map ppr flds)))
265 ppr (HsRecFields { rec_flds = flds, rec_dotdot = Just n })
266 = braces (fsep (punctuate comma (map ppr (take n flds) ++ [dotdot])))
268 dotdot = ptext SLIT("..") <+> ifPprDebug (ppr (drop n flds))
270 instance (OutputableBndr id, Outputable arg)
271 => Outputable (HsRecField id arg) where
272 ppr (HsRecField { hsRecFieldId = f, hsRecFieldArg = arg,
274 = ppr f <+> (if pun then empty else equals <+> ppr arg)
276 -- add parallel array brackets around a document
278 pabrackets :: SDoc -> SDoc
279 pabrackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
283 %************************************************************************
287 %************************************************************************
290 mkPrefixConPat :: DataCon -> [OutPat id] -> Type -> OutPat id
291 -- Make a vanilla Prefix constructor pattern
292 mkPrefixConPat dc pats ty
293 = noLoc $ ConPatOut { pat_con = noLoc dc, pat_tvs = [], pat_dicts = [],
294 pat_binds = emptyLHsBinds, pat_args = PrefixCon pats,
297 mkNilPat :: Type -> OutPat id
298 mkNilPat ty = mkPrefixConPat nilDataCon [] ty
300 mkCharLitPat :: Char -> OutPat id
301 mkCharLitPat c = mkPrefixConPat charDataCon [noLoc $ LitPat (HsCharPrim c)] charTy
303 mkCoPat :: HsWrapper -> Pat id -> Type -> Pat id
305 | isIdHsWrapper co = pat
306 | otherwise = CoPat co pat ty
308 mkCoPatCoI :: CoercionI -> Pat id -> Type -> Pat id
309 mkCoPatCoI IdCo pat ty = pat
310 mkCoPatCoI (ACo co) pat ty = mkCoPat (WpCo co) pat ty
314 %************************************************************************
316 %* Predicates for checking things about pattern-lists in EquationInfo *
318 %************************************************************************
320 \subsection[Pat-list-predicates]{Look for interesting things in patterns}
322 Unlike in the Wadler chapter, where patterns are either ``variables''
323 or ``constructors,'' here we distinguish between:
326 Patterns that cannot fail to match: variables, wildcards, and lazy
329 These are the irrefutable patterns; the two other categories
330 are refutable patterns.
333 A non-literal constructor pattern (see next category).
335 \item[literal patterns:]
336 At least the numeric ones may be overloaded.
339 A pattern is in {\em exactly one} of the above three categories; `as'
340 patterns are treated specially, of course.
342 The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
344 isWildPat (WildPat _) = True
345 isWildPat other = False
347 patsAreAllCons :: [Pat id] -> Bool
348 patsAreAllCons pat_list = all isConPat pat_list
350 isConPat (AsPat _ pat) = isConPat (unLoc pat)
351 isConPat (ConPatIn {}) = True
352 isConPat (ConPatOut {}) = True
353 isConPat (ListPat {}) = True
354 isConPat (PArrPat {}) = True
355 isConPat (TuplePat {}) = True
356 isConPat other = False
358 isSigPat (SigPatIn _ _) = True
359 isSigPat (SigPatOut _ _) = True
360 isSigPat other = False
362 patsAreAllLits :: [Pat id] -> Bool
363 patsAreAllLits pat_list = all isLitPat pat_list
365 isLitPat (AsPat _ pat) = isLitPat (unLoc pat)
366 isLitPat (LitPat _) = True
367 isLitPat (NPat _ _ _) = True
368 isLitPat (NPlusKPat _ _ _ _) = True
369 isLitPat other = False
371 isBangHsBind :: HsBind id -> Bool
372 -- In this module because HsPat is above HsBinds in the import graph
373 isBangHsBind (PatBind { pat_lhs = L _ (BangPat p) }) = True
374 isBangHsBind bind = False
376 isIrrefutableHsPat :: LPat id -> Bool
377 -- (isIrrefutableHsPat p) is true if matching against p cannot fail,
378 -- in the sense of falling through to the next pattern.
379 -- (NB: this is not quite the same as the (silly) defn
380 -- in 3.17.2 of the Haskell 98 report.)
382 -- isIrrefutableHsPat returns False if it's in doubt; specifically
383 -- on a ConPatIn it doesn't know the size of the constructor family
384 -- But if it returns True, the pattern is definitely irrefutable
385 isIrrefutableHsPat pat
388 go (L _ pat) = go1 pat
390 go1 (WildPat _) = True
391 go1 (VarPat _) = True
392 go1 (VarPatOut _ _) = True
393 go1 (LazyPat pat) = True
394 go1 (BangPat pat) = go pat
395 go1 (CoPat _ pat _) = go1 pat
396 go1 (ParPat pat) = go pat
397 go1 (AsPat _ pat) = go pat
398 go1 (ViewPat _ pat _) = go pat
399 go1 (SigPatIn pat _) = go pat
400 go1 (SigPatOut pat _) = go pat
401 go1 (TuplePat pats _ _) = all go pats
402 go1 (ListPat pats _) = False
403 go1 (PArrPat pats _) = False -- ?
405 go1 (ConPatIn _ _) = False -- Conservative
406 go1 (ConPatOut{ pat_con = L _ con, pat_args = details })
407 = isProductTyCon (dataConTyCon con)
408 && all go (hsConPatArgs details)
410 go1 (LitPat _) = False
411 go1 (NPat _ _ _) = False
412 go1 (NPlusKPat _ _ _ _) = False
414 go1 (TypePat _) = panic "isIrrefutableHsPat: type pattern"