2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[PatSyntax]{Abstract Haskell syntax---patterns}
7 #include "HsVersions.h"
13 irrefutablePat, irrefutablePats,
15 patsAreAllCons, isConPat,
16 patsAreAllLits, isLitPat,
23 import HsBasic ( HsLit, Fixity )
24 IMPORT_DELOOPER(HsLoop) ( HsExpr )
27 import Id ( dataConTyCon, GenId )
28 import Maybes ( maybeToBool )
29 import Name ( pprSym, pprNonSym )
30 import Outputable ( interppSP, interpp'SP, ifPprShowAll )
31 import PprStyle ( PprStyle(..) )
33 import TyCon ( maybeTyConSingleCon )
34 import PprType ( GenType )
37 Patterns come in distinct before- and after-typechecking flavo(u)rs.
40 = WildPatIn -- wild card
41 | VarPatIn name -- variable
42 | LitPatIn HsLit -- literal
43 | LazyPatIn (InPat name) -- lazy pattern
44 | AsPatIn name -- as pattern
46 | ConPatIn name -- constructed type
48 | ConOpPatIn (InPat name)
50 Fixity -- c.f. OpApp in HsExpr
53 -- We preserve prefix negation and parenthesis for the precedence parser.
55 | NegPatIn (InPat name) -- negated pattern
56 | ParPatIn (InPat name) -- parenthesised pattern
58 | ListPatIn [InPat name] -- syntactic list
59 -- must have >= 1 elements
60 | TuplePatIn [InPat name] -- tuple
62 | RecPatIn name -- record
63 [(name, InPat name, Bool)] -- True <=> source used punning
65 data OutPat tyvar uvar id
66 = WildPat (GenType tyvar uvar) -- wild card
68 | VarPat id -- variable (type is in the Id)
70 | LazyPat (OutPat tyvar uvar id) -- lazy pattern
72 | AsPat id -- as pattern
73 (OutPat tyvar uvar id)
75 | ConPat Id -- Constructor is always an Id
76 (GenType tyvar uvar) -- the type of the pattern
77 [OutPat tyvar uvar id]
79 | ConOpPat (OutPat tyvar uvar id) -- just a special case...
81 (OutPat tyvar uvar id)
83 | ListPat -- syntactic list
84 (GenType tyvar uvar) -- the type of the elements
85 [OutPat tyvar uvar id]
87 | TuplePat [OutPat tyvar uvar id] -- tuple
88 -- UnitPat is TuplePat []
90 | RecPat Id -- record constructor
91 (GenType tyvar uvar) -- the type of the pattern
92 [(Id, OutPat tyvar uvar id, Bool)] -- True <=> source used punning
94 | LitPat -- Used for *non-overloaded* literal patterns:
95 -- Int#, Char#, Int, Char, String, etc.
97 (GenType tyvar uvar) -- type of pattern
99 | NPat -- Used for *overloaded* literal patterns
100 HsLit -- the literal is retained so that
101 -- the desugarer can readily identify
102 -- equations with identical literal-patterns
103 (GenType tyvar uvar) -- type of pattern, t
104 (HsExpr tyvar uvar id (OutPat tyvar uvar id))
105 -- of type t -> Bool; detects match
107 | DictPat -- Used when destructing Dictionaries with an explicit case
108 [id] -- superclass dicts
113 instance (Outputable name, NamedThing name) => Outputable (InPat name) where
116 pprInPat :: (Outputable name, NamedThing name) => PprStyle -> InPat name -> Pretty
118 pprInPat sty (WildPatIn) = ppStr "_"
119 pprInPat sty (VarPatIn var) = ppr sty var
120 pprInPat sty (LitPatIn s) = ppr sty s
121 pprInPat sty (LazyPatIn pat) = ppBeside (ppChar '~') (ppr sty pat)
122 pprInPat sty (AsPatIn name pat)
123 = ppBesides [ppLparen, ppr sty name, ppChar '@', ppr sty pat, ppRparen]
125 pprInPat sty (ConPatIn c pats)
129 ppCat [ppr sty c, interppSP sty pats] -- ParPats put in the parens
131 pprInPat sty (ConOpPatIn pat1 op fixity pat2)
132 = ppCat [ppr sty pat1, ppr sty op, ppr sty pat2] -- ParPats put in parens
134 -- ToDo: use pprSym to print op (but this involves fiddling various
135 -- contexts & I'm lazy...); *PatIns are *rarely* printed anyway... (WDP)
137 pprInPat sty (NegPatIn pat)
139 pp_pat = pprInPat sty pat
141 ppBeside (ppChar '-') (
147 pprInPat sty (ParPatIn pat)
148 = ppParens (pprInPat sty pat)
150 pprInPat sty (ListPatIn pats)
151 = ppBesides [ppLbrack, interpp'SP sty pats, ppRbrack]
152 pprInPat sty (TuplePatIn pats)
153 = ppParens (interpp'SP sty pats)
155 pprInPat sty (RecPatIn con rpats)
156 = ppCat [ppr sty con, ppCurlies (ppIntersperse pp'SP (map (pp_rpat sty) rpats))]
158 pp_rpat PprForUser (v, _, True) = ppr PprForUser v
159 pp_rpat sty (v, p, _) = ppCat [ppr sty v, ppStr "=", ppr sty p]
163 instance (Eq tyvar, Outputable tyvar, Eq uvar, Outputable uvar, Outputable id)
164 => Outputable (OutPat tyvar uvar id) where
169 pprOutPat sty (WildPat ty) = ppChar '_'
170 pprOutPat sty (VarPat var) = ppr sty var
171 pprOutPat sty (LazyPat pat) = ppBesides [ppChar '~', ppr sty pat]
172 pprOutPat sty (AsPat name pat)
173 = ppBesides [ppLparen, ppr sty name, ppChar '@', ppr sty pat, ppRparen]
175 pprOutPat sty (ConPat name ty [])
176 = ppBeside (ppr sty name)
177 (ifPprShowAll sty (pprConPatTy sty ty))
179 pprOutPat sty (ConPat name ty pats)
180 = ppBesides [ppLparen, ppr sty name, ppSP,
181 interppSP sty pats, ppRparen,
182 ifPprShowAll sty (pprConPatTy sty ty) ]
184 pprOutPat sty (ConOpPat pat1 op pat2 ty)
185 = ppBesides [ppLparen, ppr sty pat1, ppSP, pprSym sty op, ppSP, ppr sty pat2, ppRparen]
187 pprOutPat sty (ListPat ty pats)
188 = ppBesides [ppLbrack, interpp'SP sty pats, ppRbrack]
189 pprOutPat sty (TuplePat pats)
190 = ppParens (interpp'SP sty pats)
192 pprOutPat sty (RecPat con ty rpats)
193 = ppBesides [ppr sty con, ppCurlies (ppIntersperse pp'SP (map (pp_rpat sty) rpats))]
195 pp_rpat PprForUser (v, _, True) = ppr PprForUser v
196 pp_rpat sty (v, p, _) = ppCat [ppr sty v, ppStr "=", ppr sty p]
198 pprOutPat sty (LitPat l ty) = ppr sty l -- ToDo: print more
199 pprOutPat sty (NPat l ty e) = ppr sty l -- ToDo: print more
201 pprOutPat sty (DictPat dicts methods)
202 = ppSep [ppBesides [ppLparen, ppPStr SLIT("{-dict-}")],
203 ppBracket (interpp'SP sty dicts),
204 ppBesides [ppBracket (interpp'SP sty methods), ppRparen]]
207 = ppParens (ppr sty ty)
210 %************************************************************************
212 %* predicates for checking things about pattern-lists in EquationInfo *
214 %************************************************************************
215 \subsection[Pat-list-predicates]{Look for interesting things in patterns}
217 Unlike in the Wadler chapter, where patterns are either ``variables''
218 or ``constructors,'' here we distinguish between:
221 Patterns that cannot fail to match: variables, wildcards, and lazy
224 These are the irrefutable patterns; the two other categories
225 are refutable patterns.
228 A non-literal constructor pattern (see next category).
230 \item[literal patterns:]
231 At least the numeric ones may be overloaded.
234 A pattern is in {\em exactly one} of the above three categories; `as'
235 patterns are treated specially, of course.
237 The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
239 irrefutablePats :: [OutPat a b c] -> Bool
240 irrefutablePats pat_list = all irrefutablePat pat_list
242 irrefutablePat (AsPat _ pat) = irrefutablePat pat
243 irrefutablePat (WildPat _) = True
244 irrefutablePat (VarPat _) = True
245 irrefutablePat (LazyPat _) = True
246 irrefutablePat (DictPat ds ms) = (length ds + length ms) <= 1
247 irrefutablePat other = False
249 failureFreePat :: OutPat a b c -> Bool
251 failureFreePat (WildPat _) = True
252 failureFreePat (VarPat _) = True
253 failureFreePat (LazyPat _) = True
254 failureFreePat (AsPat _ pat) = failureFreePat pat
255 failureFreePat (ConPat con tys pats) = only_con con && all failureFreePat pats
256 failureFreePat (ConOpPat pat1 con pat2 _) = only_con con && failureFreePat pat1 && failureFreePat pat1
257 failureFreePat (RecPat con _ fields) = only_con con && and [ failureFreePat pat | (_,pat,_) <- fields ]
258 failureFreePat (ListPat _ _) = False
259 failureFreePat (TuplePat pats) = all failureFreePat pats
260 failureFreePat (DictPat _ _) = True
261 failureFreePat other_pat = False -- Literals, NPat
263 only_con con = maybeToBool (maybeTyConSingleCon (dataConTyCon con))
267 patsAreAllCons :: [OutPat a b c] -> Bool
268 patsAreAllCons pat_list = all isConPat pat_list
270 isConPat (AsPat _ pat) = isConPat pat
271 isConPat (ConPat _ _ _) = True
272 isConPat (ConOpPat _ _ _ _) = True
273 isConPat (ListPat _ _) = True
274 isConPat (TuplePat _) = True
275 isConPat (RecPat _ _ _) = True
276 isConPat (DictPat ds ms) = (length ds + length ms) > 1
277 isConPat other = False
279 patsAreAllLits :: [OutPat a b c] -> Bool
280 patsAreAllLits pat_list = all isLitPat pat_list
282 isLitPat (AsPat _ pat) = isLitPat pat
283 isLitPat (LitPat _ _) = True
284 isLitPat (NPat _ _ _) = True
285 isLitPat other = False
288 This function @collectPatBinders@ works with the ``collectBinders''
289 functions for @HsBinds@, etc. The order in which the binders are
290 collected is important; see @HsBinds.lhs@.
292 collectPatBinders :: InPat a -> [a]
294 collectPatBinders WildPatIn = []
295 collectPatBinders (VarPatIn var) = [var]
296 collectPatBinders (LitPatIn _) = []
297 collectPatBinders (LazyPatIn pat) = collectPatBinders pat
298 collectPatBinders (AsPatIn a pat) = a : collectPatBinders pat
299 collectPatBinders (ConPatIn c pats) = concat (map collectPatBinders pats)
300 collectPatBinders (ConOpPatIn p1 c f p2) = collectPatBinders p1 ++ collectPatBinders p2
301 collectPatBinders (NegPatIn pat) = collectPatBinders pat
302 collectPatBinders (ParPatIn pat) = collectPatBinders pat
303 collectPatBinders (ListPatIn pats) = concat (map collectPatBinders pats)
304 collectPatBinders (TuplePatIn pats) = concat (map collectPatBinders pats)
305 collectPatBinders (RecPatIn c fields) = concat (map (\ (f,pat,_) -> collectPatBinders pat) fields)