2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[PatSyntax]{Abstract Haskell syntax---patterns}
8 Pat(..), InPat, OutPat, LPat,
10 HsConDetails(..), hsConArgs,
12 mkPrefixConPat, mkCharLitPat, mkNilPat, mkCoPat,
15 patsAreAllCons, isConPat, isSigPat, isWildPat,
16 patsAreAllLits, isLitPat, isIrrefutableHsPat
19 #include "HsVersions.h"
22 import {-# SOURCE #-} HsExpr ( SyntaxExpr )
25 import HsBinds ( DictBinds, HsBind(..), HsWrapper, isIdHsWrapper, pprHsWrapper,
26 emptyLHsBinds, pprLHsBinds )
27 import HsLit ( HsLit(HsCharPrim), HsOverLit )
28 import HsTypes ( LHsType, PostTcType )
29 import BasicTypes ( Boxity, tupleParens )
31 import PprCore ( {- instance OutputableBndr TyVar -} )
32 import TysWiredIn ( nilDataCon, charDataCon, charTy )
34 import DataCon ( DataCon, dataConTyCon )
35 import TyCon ( isProductTyCon )
38 import SrcLoc ( Located(..), unLoc, noLoc )
43 type InPat id = LPat id -- No 'Out' constructors
44 type OutPat id = LPat id -- No 'In' constructors
46 type LPat id = Located (Pat id)
49 = ------------ Simple patterns ---------------
50 WildPat PostTcType -- Wild card
51 | VarPat id -- Variable
52 | VarPatOut id (DictBinds id) -- Used only for overloaded Ids; the
53 -- bindings give its overloaded instances
54 | LazyPat (LPat id) -- Lazy pattern
55 | AsPat (Located id) (LPat id) -- As pattern
56 | ParPat (LPat id) -- Parenthesised pattern
57 | BangPat (LPat id) -- Bang patterng
59 ------------ Lists, tuples, arrays ---------------
60 | ListPat [LPat id] -- Syntactic list
61 PostTcType -- The type of the elements
63 | TuplePat [LPat id] -- Tuple
64 Boxity -- UnitPat is TuplePat []
66 -- You might think that the PostTcType was redundant, but it's essential
69 -- f :: (T a, a) -> Int
71 -- When desugaring, we must generate
72 -- f = /\a. \v::a. case v of (t::T a, w::a) ->
73 -- case t of (T1 (x::Int)) ->
74 -- Note the (w::a), NOT (w::Int), because we have not yet
75 -- refined 'a' to Int. So we must know that the second component
76 -- of the tuple is of type 'a' not Int. See selectMatchVar
78 | PArrPat [LPat id] -- Syntactic parallel array
79 PostTcType -- The type of the elements
81 ------------ Constructor patterns ---------------
82 | ConPatIn (Located id)
83 (HsConDetails id (LPat id))
86 pat_con :: Located DataCon,
87 pat_tvs :: [TyVar], -- Existentially bound type variables
88 -- including any bound coercion variables
89 pat_dicts :: [id], -- Ditto dictionaries
90 pat_binds :: DictBinds id, -- Bindings involving those dictionaries
91 pat_args :: HsConDetails id (LPat id),
92 pat_ty :: Type -- The type of the pattern
95 ------------ Literal and n+k patterns ---------------
96 | LitPat HsLit -- Used for *non-overloaded* literal patterns:
97 -- Int#, Char#, Int, Char, String, etc.
99 | NPat (HsOverLit id) -- ALWAYS positive
100 (Maybe (SyntaxExpr id)) -- Just (Name of 'negate') for negative
101 -- patterns, Nothing otherwise
102 (SyntaxExpr id) -- Equality checker, of type t->t->Bool
103 PostTcType -- Type of the pattern
105 | NPlusKPat (Located id) -- n+k pattern
106 (HsOverLit id) -- It'll always be an HsIntegral
107 (SyntaxExpr id) -- (>=) function, of type t->t->Bool
108 (SyntaxExpr id) -- Name of '-' (see RnEnv.lookupSyntaxName)
110 ------------ Generics ---------------
111 | TypePat (LHsType id) -- Type pattern for generic definitions
112 -- e.g f{| a+b |} = ...
113 -- These show up only in class declarations,
114 -- and should be a top-level pattern
116 ------------ Pattern type signatures ---------------
117 | SigPatIn (LPat id) -- Pattern with a type signature
120 | SigPatOut (LPat id) -- Pattern with a type signature
123 ------------ Dictionary patterns (translation only) ---------------
124 | DictPat -- Used when destructing Dictionaries with an explicit case
125 [id] -- Superclass dicts
128 ------------ Pattern coercions (translation only) ---------------
129 | CoPat HsWrapper -- If co::t1 -> t2, p::t2,
130 -- then (CoPat co p) :: t1
131 (Pat id) -- Why not LPat? Ans: existing locn will do
133 -- During desugaring a (CoPat co pat) turns into a cast with 'co' on
134 -- the scrutinee, followed by a match on 'pat'
137 HsConDetails is use both for patterns and for data type declarations
140 data HsConDetails id arg
141 = PrefixCon [arg] -- C p1 p2 p3
142 | RecCon [(Located id, arg)] -- C { x = p1, y = p2 }
143 | InfixCon arg arg -- p1 `C` p2
145 hsConArgs :: HsConDetails id arg -> [arg]
146 hsConArgs (PrefixCon ps) = ps
147 hsConArgs (RecCon fs) = map snd fs
148 hsConArgs (InfixCon p1 p2) = [p1,p2]
152 %************************************************************************
156 %************************************************************************
159 instance (OutputableBndr name) => Outputable (Pat name) where
162 pprPatBndr :: OutputableBndr name => name -> SDoc
163 pprPatBndr var -- Print with type info if -dppr-debug is on
164 = getPprStyle $ \ sty ->
165 if debugStyle sty then
166 parens (pprBndr LambdaBind var) -- Could pass the site to pprPat
167 -- but is it worth it?
171 pprPat :: (OutputableBndr name) => Pat name -> SDoc
172 pprPat (VarPat var) = pprPatBndr var
173 pprPat (VarPatOut var bs) = parens (pprPatBndr var <+> braces (ppr bs))
174 pprPat (WildPat _) = char '_'
175 pprPat (LazyPat pat) = char '~' <> ppr pat
176 pprPat (BangPat pat) = char '!' <> ppr pat
177 pprPat (AsPat name pat) = parens (hcat [ppr name, char '@', ppr pat])
178 pprPat (ParPat pat) = parens (ppr pat)
179 pprPat (ListPat pats _) = brackets (interpp'SP pats)
180 pprPat (PArrPat pats _) = pabrackets (interpp'SP pats)
181 pprPat (TuplePat pats bx _) = tupleParens bx (interpp'SP pats)
183 pprPat (ConPatIn con details) = pprUserCon con details
184 pprPat (ConPatOut { pat_con = con, pat_tvs = tvs, pat_dicts = dicts,
185 pat_binds = binds, pat_args = details })
186 = getPprStyle $ \ sty -> -- Tiresome; in TcBinds.tcRhs we print out a
187 if debugStyle sty then -- typechecked Pat in an error message,
188 -- and we want to make sure it prints nicely
189 ppr con <+> sep [ hsep (map pprPatBndr tvs) <+> hsep (map pprPatBndr dicts),
190 pprLHsBinds binds, pprConArgs details]
191 else pprUserCon con details
193 pprPat (LitPat s) = ppr s
194 pprPat (NPat l Nothing _ _) = ppr l
195 pprPat (NPat l (Just _) _ _) = char '-' <> ppr l
196 pprPat (NPlusKPat n k _ _) = hcat [ppr n, char '+', ppr k]
197 pprPat (TypePat ty) = ptext SLIT("{|") <> ppr ty <> ptext SLIT("|}")
198 pprPat (CoPat co pat _) = parens (pprHsWrapper (ppr pat) co)
199 pprPat (SigPatIn pat ty) = ppr pat <+> dcolon <+> ppr ty
200 pprPat (SigPatOut pat ty) = ppr pat <+> dcolon <+> ppr ty
201 pprPat (DictPat ds ms) = parens (sep [ptext SLIT("{-dict-}"),
202 brackets (interpp'SP ds),
203 brackets (interpp'SP ms)])
205 pprUserCon c (InfixCon p1 p2) = ppr p1 <+> ppr c <+> ppr p2
206 pprUserCon c details = ppr c <+> pprConArgs details
208 pprConArgs (PrefixCon pats) = interppSP pats
209 pprConArgs (InfixCon p1 p2) = interppSP [p1,p2]
210 pprConArgs (RecCon rpats) = braces (hsep (punctuate comma (map (pp_rpat) rpats)))
212 pp_rpat (v, p) = hsep [ppr v, char '=', ppr p]
215 -- add parallel array brackets around a document
217 pabrackets :: SDoc -> SDoc
218 pabrackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
222 %************************************************************************
226 %************************************************************************
229 mkPrefixConPat :: DataCon -> [OutPat id] -> Type -> OutPat id
230 -- Make a vanilla Prefix constructor pattern
231 mkPrefixConPat dc pats ty
232 = noLoc $ ConPatOut { pat_con = noLoc dc, pat_tvs = [], pat_dicts = [],
233 pat_binds = emptyLHsBinds, pat_args = PrefixCon pats,
236 mkNilPat :: Type -> OutPat id
237 mkNilPat ty = mkPrefixConPat nilDataCon [] ty
239 mkCharLitPat :: Char -> OutPat id
240 mkCharLitPat c = mkPrefixConPat charDataCon [noLoc $ LitPat (HsCharPrim c)] charTy
242 mkCoPat :: HsWrapper -> OutPat id -> Type -> OutPat id
243 mkCoPat co lpat@(L loc pat) ty
244 | isIdHsWrapper co = lpat
245 | otherwise = L loc (CoPat co pat ty)
249 %************************************************************************
251 %* Predicates for checking things about pattern-lists in EquationInfo *
253 %************************************************************************
255 \subsection[Pat-list-predicates]{Look for interesting things in patterns}
257 Unlike in the Wadler chapter, where patterns are either ``variables''
258 or ``constructors,'' here we distinguish between:
261 Patterns that cannot fail to match: variables, wildcards, and lazy
264 These are the irrefutable patterns; the two other categories
265 are refutable patterns.
268 A non-literal constructor pattern (see next category).
270 \item[literal patterns:]
271 At least the numeric ones may be overloaded.
274 A pattern is in {\em exactly one} of the above three categories; `as'
275 patterns are treated specially, of course.
277 The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
279 isWildPat (WildPat _) = True
280 isWildPat other = False
282 patsAreAllCons :: [Pat id] -> Bool
283 patsAreAllCons pat_list = all isConPat pat_list
285 isConPat (AsPat _ pat) = isConPat (unLoc pat)
286 isConPat (ConPatIn {}) = True
287 isConPat (ConPatOut {}) = True
288 isConPat (ListPat {}) = True
289 isConPat (PArrPat {}) = True
290 isConPat (TuplePat {}) = True
291 isConPat (DictPat ds ms) = (length ds + length ms) > 1
292 isConPat other = False
294 isSigPat (SigPatIn _ _) = True
295 isSigPat (SigPatOut _ _) = True
296 isSigPat other = False
298 patsAreAllLits :: [Pat id] -> Bool
299 patsAreAllLits pat_list = all isLitPat pat_list
301 isLitPat (AsPat _ pat) = isLitPat (unLoc pat)
302 isLitPat (LitPat _) = True
303 isLitPat (NPat _ _ _ _) = True
304 isLitPat (NPlusKPat _ _ _ _) = True
305 isLitPat other = False
307 isBangHsBind :: HsBind id -> Bool
308 -- In this module because HsPat is above HsBinds in the import graph
309 isBangHsBind (PatBind { pat_lhs = L _ (BangPat p) }) = True
310 isBangHsBind bind = False
312 isIrrefutableHsPat :: LPat id -> Bool
313 -- This function returns False if it's in doubt; specifically
314 -- on a ConPatIn it doesn't know the size of the constructor family
315 -- But if it returns True, the pattern is definitely irrefutable
316 isIrrefutableHsPat pat
319 go (L _ pat) = go1 pat
321 go1 (WildPat _) = True
322 go1 (VarPat _) = True
323 go1 (VarPatOut _ _) = True
324 go1 (LazyPat pat) = True
325 go1 (BangPat pat) = go pat
326 go1 (CoPat _ pat _) = go1 pat
327 go1 (ParPat pat) = go pat
328 go1 (AsPat _ pat) = go pat
329 go1 (SigPatIn pat _) = go pat
330 go1 (SigPatOut pat _) = go pat
331 go1 (TuplePat pats _ _) = all go pats
332 go1 (ListPat pats _) = False
333 go1 (PArrPat pats _) = False -- ?
335 go1 (ConPatIn _ _) = False -- Conservative
336 go1 (ConPatOut{ pat_con = L _ con, pat_args = details })
337 = isProductTyCon (dataConTyCon con)
338 && all go (hsConArgs details)
340 go1 (LitPat _) = False
341 go1 (NPat _ _ _ _) = False
342 go1 (NPlusKPat _ _ _ _) = False
344 go1 (TypePat _) = panic "isIrrefutableHsPat: type pattern"
345 go1 (DictPat _ _) = panic "isIrrefutableHsPat: type pattern"