@@ -3,7 +3,7 @@ module Parse.Patterns (patternTerm, patternExpr, makeLambda, flattenPatterns) wh
33
44import Ast
55import Located
6−import Control.Applicative ((<$>),(<*>))
6+import Control.Applicative ((<$>),(<*>),(*>),pure)
77import Control.Monad
88import Control.Monad.State
99import Data.Char (isUpper)
@@ -19,6 +19,12 @@ patternBasic =
1919 return $ if isUpper c then PData x [] else PVar x
2020 ]
2121
22+patternMaybeAsVar :: Pattern -> IParser Pattern
23+patternMaybeAsVar x =
24+ choice [ PAsVar <$>
25+ (optional whitespace *> reserved "as" *> whitespace *> lowVar) <*> pure x,
26+ pure x ]
27+
2228patternRecord :: IParser Pattern
2329patternRecord = PRecord <$> brackets (commaSep1 lowVar)
2430
@@ -30,14 +36,17 @@ patternList :: IParser Pattern
3036patternList = plist <$> braces (commaSep patternExpr)
3137
3238patternTerm :: IParser Pattern
33−patternTerm = choice [ patternRecord, patternTuple, patternList, patternBasic ]
34− <?> "pattern"
39+patternTerm = (choice [ patternRecord, patternTuple, patternList,
40+ patternBasic ])
41+ <?> "pattern"
3542
3643patternConstructor :: IParser Pattern
3744patternConstructor = PData <$> capVar <*> spacePrefix patternTerm
3845
3946patternExpr :: IParser Pattern
40−patternExpr = foldr1 pcons <$> consSep1 (patternConstructor <|> patternTerm) <?> "pattern"
47+patternExpr = (patternMaybeAsVar =<<
48+ (foldr1 pcons <$> consSep1 (patternConstructor <|> patternTerm)))
49+ <?> "pattern"
4150
4251makeLambda :: [Pattern] -> CExpr -> GuidCounter CExpr
4352makeLambda pats body = go (reverse pats) body
@@ -53,6 +62,10 @@ extract pattern body@(L t s _) =
5362 case pattern of
5463 PAnything -> return $ fn "_" body
5564 PVar x -> return $ fn x body
65+ PAsVar x PAnything -> return $ fn x body
66+ PAsVar x p -> do
67+ (x', body') <- extract p body
68+ return $ fn x (loc $ Let [FnDef x' [] (loc $ Var x)] body')
5669 PData name ps -> do
5770 x <- guid
5871 let a = '_' : show x
@@ -97,6 +110,10 @@ matchSingle pat exp@(L t s _) p =
97110 PVar x ->
98111 return [ FnDef x [] (loc $ Case exp [(pat, loc $ Var x)]) ]
99112
113+ PAsVar x p' -> do
114+ subPat <- matchSingle p' (loc $ Var x) p'
115+ return $ (FnDef x [] (loc $ Case exp [(pat, loc $ Var x)])):subPat
116+
100117 PRecord fs -> do
101118 a <- (\x -> '_' : show x) `liftM` guid
102119 let toDef f = FnDef f [] (loc $ Access (loc $ Var a) f)