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,
15 patsAreAllCons, isConPat, isSigPat, isWildPat,
16 patsAreAllLits, isLitPat, isIrrefutableHsPat
19 #include "HsVersions.h"
22 import {-# SOURCE #-} HsExpr ( SyntaxExpr )
25 import HsBinds ( DictBinds, HsBind(..), emptyLHsBinds, pprLHsBinds )
26 import HsLit ( HsLit(HsCharPrim), HsOverLit )
27 import HsTypes ( LHsType, PostTcType )
28 import BasicTypes ( Boxity, tupleParens )
30 import PprCore ( {- instance OutputableBndr TyVar -} )
31 import TysWiredIn ( nilDataCon, charDataCon, charTy )
33 import DataCon ( DataCon, dataConTyCon )
34 import TyCon ( isProductTyCon )
37 import SrcLoc ( Located(..), unLoc, noLoc )
42 type InPat id = LPat id -- No 'Out' constructors
43 type OutPat id = LPat id -- No 'In' constructors
45 type LPat id = Located (Pat id)
48 = ------------ Simple patterns ---------------
49 WildPat PostTcType -- Wild card
50 | VarPat id -- Variable
51 | VarPatOut id (DictBinds id) -- Used only for overloaded Ids; the
52 -- bindings give its overloaded instances
53 | LazyPat (LPat id) -- Lazy pattern
54 | AsPat (Located id) (LPat id) -- As pattern
55 | ParPat (LPat id) -- Parenthesised pattern
56 | BangPat (LPat id) -- Bang patterng
58 ------------ Lists, tuples, arrays ---------------
59 | ListPat [LPat id] -- Syntactic list
60 PostTcType -- The type of the elements
62 | TuplePat [LPat id] -- Tuple
63 Boxity -- UnitPat is TuplePat []
65 -- You might think that the PostTcType was redundant, but it's essential
68 -- f :: (T a, a) -> Int
70 -- When desugaring, we must generate
71 -- f = /\a. \v::a. case v of (t::T a, w::a) ->
72 -- case t of (T1 (x::Int)) ->
73 -- Note the (w::a), NOT (w::Int), because we have not yet
74 -- refined 'a' to Int. So we must know that the second component
75 -- of the tuple is of type 'a' not Int. See selectMatchVar
77 | PArrPat [LPat id] -- Syntactic parallel array
78 PostTcType -- The type of the elements
80 ------------ Constructor patterns ---------------
81 | ConPatIn (Located id)
82 (HsConDetails id (LPat id))
84 | ConPatOut (Located DataCon)
85 [TyVar] -- Existentially bound type variables
86 [id] -- Ditto dictionaries
87 (DictBinds id) -- Bindings involving those dictionaries
88 (HsConDetails id (LPat id))
89 Type -- The type of the pattern
91 ------------ Literal and n+k patterns ---------------
92 | LitPat HsLit -- Used for *non-overloaded* literal patterns:
93 -- Int#, Char#, Int, Char, String, etc.
95 | NPat (HsOverLit id) -- ALWAYS positive
96 (Maybe (SyntaxExpr id)) -- Just (Name of 'negate') for negative
97 -- patterns, Nothing otherwise
98 (SyntaxExpr id) -- Equality checker, of type t->t->Bool
99 PostTcType -- Type of the pattern
101 | NPlusKPat (Located id) -- n+k pattern
102 (HsOverLit id) -- It'll always be an HsIntegral
103 (SyntaxExpr id) -- (>=) function, of type t->t->Bool
104 (SyntaxExpr id) -- Name of '-' (see RnEnv.lookupSyntaxName)
106 ------------ Generics ---------------
107 | TypePat (LHsType id) -- Type pattern for generic definitions
108 -- e.g f{| a+b |} = ...
109 -- These show up only in class declarations,
110 -- and should be a top-level pattern
112 ------------ Pattern type signatures ---------------
113 | SigPatIn (LPat id) -- Pattern with a type signature
116 | SigPatOut (LPat id) -- Pattern with a type signature
119 ------------ Dictionary patterns (translation only) ---------------
120 | DictPat -- Used when destructing Dictionaries with an explicit case
121 [id] -- superclass dicts
125 HsConDetails is use both for patterns and for data type declarations
128 data HsConDetails id arg
129 = PrefixCon [arg] -- C p1 p2 p3
130 | RecCon [(Located id, arg)] -- C { x = p1, y = p2 }
131 | InfixCon arg arg -- p1 `C` p2
133 hsConArgs :: HsConDetails id arg -> [arg]
134 hsConArgs (PrefixCon ps) = ps
135 hsConArgs (RecCon fs) = map snd fs
136 hsConArgs (InfixCon p1 p2) = [p1,p2]
140 %************************************************************************
144 %************************************************************************
147 instance (OutputableBndr name) => Outputable (Pat name) where
150 pprPatBndr :: OutputableBndr name => name -> SDoc
151 pprPatBndr var -- Print with type info if -dppr-debug is on
152 = getPprStyle $ \ sty ->
153 if debugStyle sty then
154 parens (pprBndr LambdaBind var) -- Could pass the site to pprPat
155 -- but is it worth it?
159 pprPat :: (OutputableBndr name) => Pat name -> SDoc
160 pprPat (VarPat var) = pprPatBndr var
161 pprPat (VarPatOut var bs) = parens (pprPatBndr var <+> braces (ppr bs))
162 pprPat (WildPat _) = char '_'
163 pprPat (LazyPat pat) = char '~' <> ppr pat
164 pprPat (BangPat pat) = char '!' <> ppr pat
165 pprPat (AsPat name pat) = parens (hcat [ppr name, char '@', ppr pat])
166 pprPat (ParPat pat) = parens (ppr pat)
167 pprPat (ListPat pats _) = brackets (interpp'SP pats)
168 pprPat (PArrPat pats _) = pabrackets (interpp'SP pats)
169 pprPat (TuplePat pats bx _) = tupleParens bx (interpp'SP pats)
171 pprPat (ConPatIn con details) = pprUserCon con details
172 pprPat (ConPatOut con tvs dicts binds details _)
173 = getPprStyle $ \ sty -> -- Tiresome; in TcBinds.tcRhs we print out a
174 if debugStyle sty then -- typechecked Pat in an error message,
175 -- and we want to make sure it prints nicely
176 ppr con <+> sep [ hsep (map pprPatBndr tvs) <+> hsep (map pprPatBndr dicts),
177 pprLHsBinds binds, pprConArgs details]
178 else pprUserCon con details
180 pprPat (LitPat s) = ppr s
181 pprPat (NPat l Nothing _ _) = ppr l
182 pprPat (NPat l (Just _) _ _) = char '-' <> ppr l
183 pprPat (NPlusKPat n k _ _) = hcat [ppr n, char '+', ppr k]
184 pprPat (TypePat ty) = ptext SLIT("{|") <> ppr ty <> ptext SLIT("|}")
185 pprPat (SigPatIn pat ty) = ppr pat <+> dcolon <+> ppr ty
186 pprPat (SigPatOut pat ty) = ppr pat <+> dcolon <+> ppr ty
187 pprPat (DictPat ds ms) = parens (sep [ptext SLIT("{-dict-}"),
188 brackets (interpp'SP ds),
189 brackets (interpp'SP ms)])
191 pprUserCon c (InfixCon p1 p2) = ppr p1 <+> ppr c <+> ppr p2
192 pprUserCon c details = ppr c <+> pprConArgs details
194 pprConArgs (PrefixCon pats) = interppSP pats
195 pprConArgs (InfixCon p1 p2) = interppSP [p1,p2]
196 pprConArgs (RecCon rpats) = braces (hsep (punctuate comma (map (pp_rpat) rpats)))
198 pp_rpat (v, p) = hsep [ppr v, char '=', ppr p]
201 -- add parallel array brackets around a document
203 pabrackets :: SDoc -> SDoc
204 pabrackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
208 %************************************************************************
212 %************************************************************************
215 mkPrefixConPat :: DataCon -> [OutPat id] -> Type -> OutPat id
216 -- Make a vanilla Prefix constructor pattern
217 mkPrefixConPat dc pats ty = noLoc $ ConPatOut (noLoc dc) [] [] emptyLHsBinds (PrefixCon pats) ty
219 mkNilPat :: Type -> OutPat id
220 mkNilPat ty = mkPrefixConPat nilDataCon [] ty
222 mkCharLitPat :: Char -> OutPat id
223 mkCharLitPat c = mkPrefixConPat charDataCon [noLoc $ LitPat (HsCharPrim c)] charTy
227 %************************************************************************
229 %* Predicates for checking things about pattern-lists in EquationInfo *
231 %************************************************************************
233 \subsection[Pat-list-predicates]{Look for interesting things in patterns}
235 Unlike in the Wadler chapter, where patterns are either ``variables''
236 or ``constructors,'' here we distinguish between:
239 Patterns that cannot fail to match: variables, wildcards, and lazy
242 These are the irrefutable patterns; the two other categories
243 are refutable patterns.
246 A non-literal constructor pattern (see next category).
248 \item[literal patterns:]
249 At least the numeric ones may be overloaded.
252 A pattern is in {\em exactly one} of the above three categories; `as'
253 patterns are treated specially, of course.
255 The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
257 isWildPat (WildPat _) = True
258 isWildPat other = False
260 patsAreAllCons :: [Pat id] -> Bool
261 patsAreAllCons pat_list = all isConPat pat_list
263 isConPat (AsPat _ pat) = isConPat (unLoc pat)
264 isConPat (ConPatIn _ _) = True
265 isConPat (ConPatOut _ _ _ _ _ _) = True
266 isConPat (ListPat _ _) = True
267 isConPat (PArrPat _ _) = True
268 isConPat (TuplePat _ _ _) = True
269 isConPat (DictPat ds ms) = (length ds + length ms) > 1
270 isConPat other = False
272 isSigPat (SigPatIn _ _) = True
273 isSigPat (SigPatOut _ _) = True
274 isSigPat other = False
276 patsAreAllLits :: [Pat id] -> Bool
277 patsAreAllLits pat_list = all isLitPat pat_list
279 isLitPat (AsPat _ pat) = isLitPat (unLoc pat)
280 isLitPat (LitPat _) = True
281 isLitPat (NPat _ _ _ _) = True
282 isLitPat (NPlusKPat _ _ _ _) = True
283 isLitPat other = False
285 isBangHsBind :: HsBind id -> Bool
286 -- In this module because HsPat is above HsBinds in the import graph
287 isBangHsBind (PatBind { pat_lhs = L _ (BangPat p) }) = True
288 isBangHsBind bind = False
290 isIrrefutableHsPat :: LPat id -> Bool
291 -- This function returns False if it's in doubt; specifically
292 -- on a ConPatIn it doesn't know the size of the constructor family
293 -- But if it returns True, the pattern is definitely irrefutable
294 isIrrefutableHsPat pat
297 go (L _ pat) = go1 pat
299 go1 (WildPat _) = True
300 go1 (VarPat _) = True
301 go1 (VarPatOut _ _) = True
302 go1 (LazyPat pat) = True
303 go1 (BangPat pat) = go pat
304 go1 (ParPat pat) = go pat
305 go1 (AsPat _ pat) = go pat
306 go1 (SigPatIn pat _) = go pat
307 go1 (SigPatOut pat _) = go pat
308 go1 (TuplePat pats _ _) = all go pats
309 go1 (ListPat pats _) = False
310 go1 (PArrPat pats _) = False -- ?
312 go1 (ConPatIn _ _) = False -- Conservative
313 go1 (ConPatOut (L _ con) _ _ _ details _)
314 = isProductTyCon (dataConTyCon con)
315 && all go (hsConArgs details)
317 go1 (LitPat _) = False
318 go1 (NPat _ _ _ _) = False
319 go1 (NPlusKPat _ _ _ _) = False
321 go1 (TypePat _) = panic "isIrrefutableHsPat: type pattern"
322 go1 (DictPat _ _) = panic "isIrrefutableHsPat: type pattern"