Improved error type with position annotation

[cc1516.git] / src / yard.icl

diff --git a/src/yard.icl b/src/yard.icl
index 2f3c90a..278bac8 100644 (file)
--- a/src/yard.icl
+++ b/src/yard.icl
@@ -3,6 +3,7 @@ implementation module yard
 import StdTuple
 import StdClass
 import StdString
+import StdList
 import Data.Functor
 import Data.Either
 import Control.Monad
@@ -13,6 +14,10 @@ instance toString Error where
        toString ParseError = "General parse error"
        toString (LexError e) = "Lexer error: " +++ e
 
+instance + Error where
+    (+) (Expected as _) (Expected bs p) = Expected (as++bs) p
+    (+) _ r                             = r
+
 runParser :: (Parser a b) [a] -> (Either Error b, [a])
 runParser (Parser f) i = f i
 
@@ -32,7 +37,15 @@ 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 _, rest)  = runParser p2 i
+        (Left e1, rest) = case runParser p2 i of
+            (Right r, rest) = (Right r, rest)
+            (Left e2, rest) = (Left (e1+e2), 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
+(<?>) p (e,pos) = Parser \i -> case runParser p i of
+    (Left e1, rest) = let error = (e1+(Expected [e] pos)) in (Left error, rest)
+    (Right r, rest) = (Right r, rest)
 
 fail :: Parser a b
 fail = empty