Added until operator

diff --git a/src/yard.dcl b/src/yard.dcl
index a029c4b..38ce368 100644 (file)
--- a/src/yard.dcl
+++ b/src/yard.dcl
@@ -25,6 +25,7 @@ top :: Parser a a
 peek :: Parser a a
 satisfy :: (a -> Bool) -> Parser a a
 check :: (a -> Bool) -> Parser a a
+until :: (Parser a b) (Parser a c) -> Parser a [b]
 item :: a -> Parser a a | Eq a
 list :: [a] -> Parser a [a] | Eq a
 eof :: Parser a Void

diff --git a/src/yard.icl b/src/yard.icl
index 582ea1d..9ed6077 100644 (file)
--- a/src/yard.icl
+++ b/src/yard.icl
@@ -37,15 +37,15 @@ instance Applicative (Parser a) where
 instance Monad (Parser a) where
     bind p f    = Parser \i -> case runParser p i of
         (Right r, rest) = runParser (f r) rest
-        (Left e, rest)  = (Left e, rest)
+        (Left e, _)     = (Left e, i)
 
 instance Alternative (Parser a) where
     empty       = Parser \i -> (Left ParseError, i)
     (<|>) p1 p2 = Parser \i -> case runParser p1 i of
         (Right r, rest) = (Right r, rest)
         (Left e1, rest) = case runParser p2 i of
-            (Left e2, rest)  = (Left $ e1+e2, rest)
-            (Right r, rest) = (Right r, rest)
+            (Left e2, rest)  = (Left $ e1+e2, i)
+            (Right r, rest)  = (Right r, rest)
 
 //Try the parser, if it fails decorate the error with Expected of the given String and position
 (<?>) :: (Parser a b) (String, Int) -> Parser a b
@@ -66,6 +66,24 @@ peek = Parser \i -> case i of
     []      = (Left ParseError, [])
     [x:xs]  = (Right x, [x:xs])
 
+//runs the left parser until the right parser succeeds. Returns the result of the left parser 
+//Note: if the right parser consumes input then this input is lost!
+//If the left parser fails before the right parser succeeds the whole parser fails
+until :: (Parser a b) (Parser a c) -> Parser a [b]
+until p guard = try $ until` p guard [] 
+    where
+        until` :: (Parser a b) (Parser a c) [b] -> Parser a [b]
+        until` p guard acc = Parser \i -> case runParser guard i of 
+            (Right _, rest) = (Right acc, rest)
+            (Left _, _)     = case runParser p i of
+                (Right r, rest) = runParser (until` p guard [r:acc]) rest
+                (Left e, _)     = (Left e, i)
+        try :: (Parser a b) -> Parser a b
+        try p = Parser \i -> case runParser p i of
+            (Left e, _)     = (Left e, i)
+            (Right r, rest) = (Right r, rest)
+
+
 eof :: Parser a Void
 eof = Parser \i -> case i of 
     []      = (Right Void, [])