Improved error reporting with positions

[cc1516.git] / src / yard.icl

diff --git a/src/yard.icl b/src/yard.icl
index 5460312..932999a 100644 (file)
--- a/src/yard.icl
+++ b/src/yard.icl
@@ -4,6 +4,9 @@ import StdTuple
 import StdClass
 import StdString
 import StdList
+import StdInt
+from Data.List import intersperse
+from Text import instance Text String, class Text(concat)
 import Data.Functor
 import Data.Either
 import Control.Monad
@@ -13,10 +16,12 @@ from Data.Func import $
 instance toString Error where
        toString ParseError = "General parse error"
        toString (LexError e) = "Lexer error: " +++ e
+    toString (Expected ts pos) = "Expected " +++ (concat $ intersperse ", " ts) 
+                                             +++ " at position " +++ (toString pos)
 
 instance + Error where
-    (+) (Expected as) (Expected bs) = Expected (as++bs)
-    (+) _ r                         = r
+    (+) (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
@@ -41,9 +46,10 @@ instance Alternative (Parser a) where
             (Right r, rest) = (Right r, rest)
             (Left e2, rest) = (Left (e1+e2), rest)
 
-<?> :: (Parser a b) String -> Parser a b
-<?> p e = Parser \i -> case runParser p i of
-    (Left e1, rest) = (Left (e1+(Expected [e])), 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