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(..), ExprCoFn, isIdCoercion, pprCoFn,
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 ExprCoFn -- If co::t1 -> t2, p::t2,
130 -- then (CoPat co p) :: t1
131 (Pat id) -- No nested location reqd
135 HsConDetails is use both for patterns and for data type declarations
138 data HsConDetails id arg
139 = PrefixCon [arg] -- C p1 p2 p3
140 | RecCon [(Located id, arg)] -- C { x = p1, y = p2 }
141 | InfixCon arg arg -- p1 `C` p2
143 hsConArgs :: HsConDetails id arg -> [arg]
144 hsConArgs (PrefixCon ps) = ps
145 hsConArgs (RecCon fs) = map snd fs
146 hsConArgs (InfixCon p1 p2) = [p1,p2]
150 %************************************************************************
154 %************************************************************************
157 instance (OutputableBndr name) => Outputable (Pat name) where
160 pprPatBndr :: OutputableBndr name => name -> SDoc
161 pprPatBndr var -- Print with type info if -dppr-debug is on
162 = getPprStyle $ \ sty ->
163 if debugStyle sty then
164 parens (pprBndr LambdaBind var) -- Could pass the site to pprPat
165 -- but is it worth it?
169 pprPat :: (OutputableBndr name) => Pat name -> SDoc
170 pprPat (VarPat var) = pprPatBndr var
171 pprPat (VarPatOut var bs) = parens (pprPatBndr var <+> braces (ppr bs))
172 pprPat (WildPat _) = char '_'
173 pprPat (LazyPat pat) = char '~' <> ppr pat
174 pprPat (BangPat pat) = char '!' <> ppr pat
175 pprPat (AsPat name pat) = parens (hcat [ppr name, char '@', ppr pat])
176 pprPat (ParPat pat) = parens (ppr pat)
177 pprPat (ListPat pats _) = brackets (interpp'SP pats)
178 pprPat (PArrPat pats _) = pabrackets (interpp'SP pats)
179 pprPat (TuplePat pats bx _) = tupleParens bx (interpp'SP pats)
181 pprPat (ConPatIn con details) = pprUserCon con details
182 pprPat (ConPatOut { pat_con = con, pat_tvs = tvs, pat_dicts = dicts,
183 pat_binds = binds, pat_args = details })
184 = getPprStyle $ \ sty -> -- Tiresome; in TcBinds.tcRhs we print out a
185 if debugStyle sty then -- typechecked Pat in an error message,
186 -- and we want to make sure it prints nicely
187 ppr con <+> sep [ hsep (map pprPatBndr tvs) <+> hsep (map pprPatBndr dicts),
188 pprLHsBinds binds, pprConArgs details]
189 else pprUserCon con details
191 pprPat (LitPat s) = ppr s
192 pprPat (NPat l Nothing _ _) = ppr l
193 pprPat (NPat l (Just _) _ _) = char '-' <> ppr l
194 pprPat (NPlusKPat n k _ _) = hcat [ppr n, char '+', ppr k]
195 pprPat (TypePat ty) = ptext SLIT("{|") <> ppr ty <> ptext SLIT("|}")
196 pprPat (CoPat co pat _) = parens (pprCoFn (ppr pat) co)
197 pprPat (SigPatIn pat ty) = ppr pat <+> dcolon <+> ppr ty
198 pprPat (SigPatOut pat ty) = ppr pat <+> dcolon <+> ppr ty
199 pprPat (DictPat ds ms) = parens (sep [ptext SLIT("{-dict-}"),
200 brackets (interpp'SP ds),
201 brackets (interpp'SP ms)])
203 pprUserCon c (InfixCon p1 p2) = ppr p1 <+> ppr c <+> ppr p2
204 pprUserCon c details = ppr c <+> pprConArgs details
206 pprConArgs (PrefixCon pats) = interppSP pats
207 pprConArgs (InfixCon p1 p2) = interppSP [p1,p2]
208 pprConArgs (RecCon rpats) = braces (hsep (punctuate comma (map (pp_rpat) rpats)))
210 pp_rpat (v, p) = hsep [ppr v, char '=', ppr p]
213 -- add parallel array brackets around a document
215 pabrackets :: SDoc -> SDoc
216 pabrackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
220 %************************************************************************
224 %************************************************************************
227 mkPrefixConPat :: DataCon -> [OutPat id] -> Type -> OutPat id
228 -- Make a vanilla Prefix constructor pattern
229 mkPrefixConPat dc pats ty
230 = noLoc $ ConPatOut { pat_con = noLoc dc, pat_tvs = [], pat_dicts = [],
231 pat_binds = emptyLHsBinds, pat_args = PrefixCon pats,
234 mkNilPat :: Type -> OutPat id
235 mkNilPat ty = mkPrefixConPat nilDataCon [] ty
237 mkCharLitPat :: Char -> OutPat id
238 mkCharLitPat c = mkPrefixConPat charDataCon [noLoc $ LitPat (HsCharPrim c)] charTy
240 mkCoPat :: ExprCoFn -> OutPat id -> Type -> OutPat id
241 mkCoPat co lpat@(L loc pat) ty
242 | isIdCoercion co = lpat
243 | otherwise = L loc (CoPat co pat ty)
247 %************************************************************************
249 %* Predicates for checking things about pattern-lists in EquationInfo *
251 %************************************************************************
253 \subsection[Pat-list-predicates]{Look for interesting things in patterns}
255 Unlike in the Wadler chapter, where patterns are either ``variables''
256 or ``constructors,'' here we distinguish between:
259 Patterns that cannot fail to match: variables, wildcards, and lazy
262 These are the irrefutable patterns; the two other categories
263 are refutable patterns.
266 A non-literal constructor pattern (see next category).
268 \item[literal patterns:]
269 At least the numeric ones may be overloaded.
272 A pattern is in {\em exactly one} of the above three categories; `as'
273 patterns are treated specially, of course.
275 The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
277 isWildPat (WildPat _) = True
278 isWildPat other = False
280 patsAreAllCons :: [Pat id] -> Bool
281 patsAreAllCons pat_list = all isConPat pat_list
283 isConPat (AsPat _ pat) = isConPat (unLoc pat)
284 isConPat (ConPatIn {}) = True
285 isConPat (ConPatOut {}) = True
286 isConPat (ListPat {}) = True
287 isConPat (PArrPat {}) = True
288 isConPat (TuplePat {}) = True
289 isConPat (DictPat ds ms) = (length ds + length ms) > 1
290 isConPat other = False
292 isSigPat (SigPatIn _ _) = True
293 isSigPat (SigPatOut _ _) = True
294 isSigPat other = False
296 patsAreAllLits :: [Pat id] -> Bool
297 patsAreAllLits pat_list = all isLitPat pat_list
299 isLitPat (AsPat _ pat) = isLitPat (unLoc pat)
300 isLitPat (LitPat _) = True
301 isLitPat (NPat _ _ _ _) = True
302 isLitPat (NPlusKPat _ _ _ _) = True
303 isLitPat other = False
305 isBangHsBind :: HsBind id -> Bool
306 -- In this module because HsPat is above HsBinds in the import graph
307 isBangHsBind (PatBind { pat_lhs = L _ (BangPat p) }) = True
308 isBangHsBind bind = False
310 isIrrefutableHsPat :: LPat id -> Bool
311 -- This function returns False if it's in doubt; specifically
312 -- on a ConPatIn it doesn't know the size of the constructor family
313 -- But if it returns True, the pattern is definitely irrefutable
314 isIrrefutableHsPat pat
317 go (L _ pat) = go1 pat
319 go1 (WildPat _) = True
320 go1 (VarPat _) = True
321 go1 (VarPatOut _ _) = True
322 go1 (LazyPat pat) = True
323 go1 (BangPat pat) = go pat
324 go1 (CoPat _ pat _) = go1 pat
325 go1 (ParPat pat) = go pat
326 go1 (AsPat _ pat) = go pat
327 go1 (SigPatIn pat _) = go pat
328 go1 (SigPatOut pat _) = go pat
329 go1 (TuplePat pats _ _) = all go pats
330 go1 (ListPat pats _) = False
331 go1 (PArrPat pats _) = False -- ?
333 go1 (ConPatIn _ _) = False -- Conservative
334 go1 (ConPatOut{ pat_con = L _ con, pat_args = details })
335 = isProductTyCon (dataConTyCon con)
336 && all go (hsConArgs details)
338 go1 (LitPat _) = False
339 go1 (NPat _ _ _ _) = False
340 go1 (NPlusKPat _ _ _ _) = False
342 go1 (TypePat _) = panic "isIrrefutableHsPat: type pattern"
343 go1 (DictPat _ _) = panic "isIrrefutableHsPat: type pattern"