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, 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))
85 pat_con :: Located DataCon,
86 pat_tvs :: [TyVar], -- Existentially bound type variables
87 -- including any bound coercion variables
88 pat_dicts :: [id], -- Ditto dictionaries
89 pat_binds :: DictBinds id, -- Bindings involving those dictionaries
90 pat_args :: HsConDetails id (LPat id),
91 pat_ty :: Type -- The type of the pattern
94 ------------ Literal and n+k patterns ---------------
95 | LitPat HsLit -- Used for *non-overloaded* literal patterns:
96 -- Int#, Char#, Int, Char, String, etc.
98 | NPat (HsOverLit id) -- ALWAYS positive
99 (Maybe (SyntaxExpr id)) -- Just (Name of 'negate') for negative
100 -- patterns, Nothing otherwise
101 (SyntaxExpr id) -- Equality checker, of type t->t->Bool
102 PostTcType -- Type of the pattern
104 | NPlusKPat (Located id) -- n+k pattern
105 (HsOverLit id) -- It'll always be an HsIntegral
106 (SyntaxExpr id) -- (>=) function, of type t->t->Bool
107 (SyntaxExpr id) -- Name of '-' (see RnEnv.lookupSyntaxName)
109 ------------ Generics ---------------
110 | TypePat (LHsType id) -- Type pattern for generic definitions
111 -- e.g f{| a+b |} = ...
112 -- These show up only in class declarations,
113 -- and should be a top-level pattern
115 ------------ Pattern type signatures ---------------
116 | SigPatIn (LPat id) -- Pattern with a type signature
119 | SigPatOut (LPat id) -- Pattern with a type signature
122 ------------ Dictionary patterns (translation only) ---------------
123 | DictPat -- Used when destructing Dictionaries with an explicit case
124 [id] -- superclass dicts
127 ------------ Pattern coercions (translation only) ---------------
128 | CoPat ExprCoFn -- If co::t1 -> t2, p::t2,
129 -- then (CoPat co p) :: t1
130 (Pat id) -- No nested location reqd
134 HsConDetails is use both for patterns and for data type declarations
137 data HsConDetails id arg
138 = PrefixCon [arg] -- C p1 p2 p3
139 | RecCon [(Located id, arg)] -- C { x = p1, y = p2 }
140 | InfixCon arg arg -- p1 `C` p2
142 hsConArgs :: HsConDetails id arg -> [arg]
143 hsConArgs (PrefixCon ps) = ps
144 hsConArgs (RecCon fs) = map snd fs
145 hsConArgs (InfixCon p1 p2) = [p1,p2]
149 %************************************************************************
153 %************************************************************************
156 instance (OutputableBndr name) => Outputable (Pat name) where
159 pprPatBndr :: OutputableBndr name => name -> SDoc
160 pprPatBndr var -- Print with type info if -dppr-debug is on
161 = getPprStyle $ \ sty ->
162 if debugStyle sty then
163 parens (pprBndr LambdaBind var) -- Could pass the site to pprPat
164 -- but is it worth it?
168 pprPat :: (OutputableBndr name) => Pat name -> SDoc
169 pprPat (VarPat var) = pprPatBndr var
170 pprPat (VarPatOut var bs) = parens (pprPatBndr var <+> braces (ppr bs))
171 pprPat (WildPat _) = char '_'
172 pprPat (LazyPat pat) = char '~' <> ppr pat
173 pprPat (BangPat pat) = char '!' <> ppr pat
174 pprPat (AsPat name pat) = parens (hcat [ppr name, char '@', ppr pat])
175 pprPat (ParPat pat) = parens (ppr pat)
176 pprPat (ListPat pats _) = brackets (interpp'SP pats)
177 pprPat (PArrPat pats _) = pabrackets (interpp'SP pats)
178 pprPat (TuplePat pats bx _) = tupleParens bx (interpp'SP pats)
180 pprPat (ConPatIn con details) = pprUserCon con details
181 pprPat (ConPatOut { pat_con = con, pat_tvs = tvs, pat_dicts = dicts,
182 pat_binds = binds, pat_args = details })
183 = getPprStyle $ \ sty -> -- Tiresome; in TcBinds.tcRhs we print out a
184 if debugStyle sty then -- typechecked Pat in an error message,
185 -- and we want to make sure it prints nicely
186 ppr con <+> sep [ hsep (map pprPatBndr tvs) <+> hsep (map pprPatBndr dicts),
187 pprLHsBinds binds, pprConArgs details]
188 else pprUserCon con details
190 pprPat (LitPat s) = ppr s
191 pprPat (NPat l Nothing _ _) = ppr l
192 pprPat (NPat l (Just _) _ _) = char '-' <> ppr l
193 pprPat (NPlusKPat n k _ _) = hcat [ppr n, char '+', ppr k]
194 pprPat (TypePat ty) = ptext SLIT("{|") <> ppr ty <> ptext SLIT("|}")
195 pprPat (CoPat co pat _) = parens (ppr co) <+> ptext SLIT("`cast`") <+> ppr pat
196 pprPat (SigPatIn pat ty) = ppr pat <+> dcolon <+> ppr ty
197 pprPat (SigPatOut pat ty) = ppr pat <+> dcolon <+> ppr ty
198 pprPat (DictPat ds ms) = parens (sep [ptext SLIT("{-dict-}"),
199 brackets (interpp'SP ds),
200 brackets (interpp'SP ms)])
202 pprUserCon c (InfixCon p1 p2) = ppr p1 <+> ppr c <+> ppr p2
203 pprUserCon c details = ppr c <+> pprConArgs details
205 pprConArgs (PrefixCon pats) = interppSP pats
206 pprConArgs (InfixCon p1 p2) = interppSP [p1,p2]
207 pprConArgs (RecCon rpats) = braces (hsep (punctuate comma (map (pp_rpat) rpats)))
209 pp_rpat (v, p) = hsep [ppr v, char '=', ppr p]
212 -- add parallel array brackets around a document
214 pabrackets :: SDoc -> SDoc
215 pabrackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
219 %************************************************************************
223 %************************************************************************
226 mkPrefixConPat :: DataCon -> [OutPat id] -> Type -> OutPat id
227 -- Make a vanilla Prefix constructor pattern
228 mkPrefixConPat dc pats ty
229 = noLoc $ ConPatOut { pat_con = noLoc dc, pat_tvs = [], pat_dicts = [],
230 pat_binds = emptyLHsBinds, pat_args = PrefixCon pats,
233 mkNilPat :: Type -> OutPat id
234 mkNilPat ty = mkPrefixConPat nilDataCon [] ty
236 mkCharLitPat :: Char -> OutPat id
237 mkCharLitPat c = mkPrefixConPat charDataCon [noLoc $ LitPat (HsCharPrim c)] charTy
239 mkCoPat :: ExprCoFn -> OutPat id -> Type -> OutPat id
240 mkCoPat co lpat@(L loc pat) ty
241 | isIdCoercion co = lpat
242 | otherwise = L loc (CoPat co pat ty)
246 %************************************************************************
248 %* Predicates for checking things about pattern-lists in EquationInfo *
250 %************************************************************************
252 \subsection[Pat-list-predicates]{Look for interesting things in patterns}
254 Unlike in the Wadler chapter, where patterns are either ``variables''
255 or ``constructors,'' here we distinguish between:
258 Patterns that cannot fail to match: variables, wildcards, and lazy
261 These are the irrefutable patterns; the two other categories
262 are refutable patterns.
265 A non-literal constructor pattern (see next category).
267 \item[literal patterns:]
268 At least the numeric ones may be overloaded.
271 A pattern is in {\em exactly one} of the above three categories; `as'
272 patterns are treated specially, of course.
274 The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
276 isWildPat (WildPat _) = True
277 isWildPat other = False
279 patsAreAllCons :: [Pat id] -> Bool
280 patsAreAllCons pat_list = all isConPat pat_list
282 isConPat (AsPat _ pat) = isConPat (unLoc pat)
283 isConPat (ConPatIn {}) = True
284 isConPat (ConPatOut {}) = True
285 isConPat (ListPat {}) = True
286 isConPat (PArrPat {}) = True
287 isConPat (TuplePat {}) = True
288 isConPat (DictPat ds ms) = (length ds + length ms) > 1
289 isConPat other = False
291 isSigPat (SigPatIn _ _) = True
292 isSigPat (SigPatOut _ _) = True
293 isSigPat other = False
295 patsAreAllLits :: [Pat id] -> Bool
296 patsAreAllLits pat_list = all isLitPat pat_list
298 isLitPat (AsPat _ pat) = isLitPat (unLoc pat)
299 isLitPat (LitPat _) = True
300 isLitPat (NPat _ _ _ _) = True
301 isLitPat (NPlusKPat _ _ _ _) = True
302 isLitPat other = False
304 isBangHsBind :: HsBind id -> Bool
305 -- In this module because HsPat is above HsBinds in the import graph
306 isBangHsBind (PatBind { pat_lhs = L _ (BangPat p) }) = True
307 isBangHsBind bind = False
309 isIrrefutableHsPat :: LPat id -> Bool
310 -- This function returns False if it's in doubt; specifically
311 -- on a ConPatIn it doesn't know the size of the constructor family
312 -- But if it returns True, the pattern is definitely irrefutable
313 isIrrefutableHsPat pat
316 go (L _ pat) = go1 pat
318 go1 (WildPat _) = True
319 go1 (VarPat _) = True
320 go1 (VarPatOut _ _) = True
321 go1 (LazyPat pat) = True
322 go1 (BangPat pat) = go pat
323 go1 (CoPat _ pat _) = go1 pat
324 go1 (ParPat pat) = go pat
325 go1 (AsPat _ pat) = go pat
326 go1 (SigPatIn pat _) = go pat
327 go1 (SigPatOut pat _) = go pat
328 go1 (TuplePat pats _ _) = all go pats
329 go1 (ListPat pats _) = False
330 go1 (PArrPat pats _) = False -- ?
332 go1 (ConPatIn _ _) = False -- Conservative
333 go1 (ConPatOut{ pat_con = L _ con, pat_args = details })
334 = isProductTyCon (dataConTyCon con)
335 && all go (hsConArgs details)
337 go1 (LitPat _) = False
338 go1 (NPat _ _ _ _) = False
339 go1 (NPlusKPat _ _ _ _) = False
341 go1 (TypePat _) = panic "isIrrefutableHsPat: type pattern"
342 go1 (DictPat _ _) = panic "isIrrefutableHsPat: type pattern"