From a0cf809b53126a797667fb43f8496a7cc2b7252e Mon Sep 17 00:00:00 2001
From: pimjager <pim@pimjager.nl>
Date: Mon, 29 Feb 2016 13:29:47 +0100
Subject: [PATCH] Improved error type with position annotation

---
 src/parse.icl |  2 +-
 src/yard.dcl  |  3 ++-
 src/yard.icl  | 11 ++++++-----
 3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/src/parse.icl b/src/parse.icl
index bc93239..5fc8f8c 100644
--- a/src/parse.icl
+++ b/src/parse.icl
@@ -173,7 +173,7 @@ trans1 :: TokenValue a -> Parser Token a
 trans1 t r = trans2 t $ const r
 
 satTok :: TokenValue -> Parser Token Token
-satTok t = satisfy ((===) t)
+satTok t = top >>= \tok=:(pos, tv) -> if (t === tok) (return tok) (fail <?> ("Token", pos))
 
 parseSepList :: TokenValue (Parser Token a) -> Parser Token [a]
 parseSepList sep p = 
diff --git a/src/yard.dcl b/src/yard.dcl
index 266eb75..73a82c0 100644
--- a/src/yard.dcl
+++ b/src/yard.dcl
@@ -7,7 +7,7 @@ from Data.Functor import class Functor
 from Control.Monad import class Monad
 from Control.Applicative import class Applicative, class Alternative
 
-:: Error = ParseError | LexError String | Expected [String]
+:: Error = ParseError | LexError String | Expected [String] Int
 :: Parser a b = Parser ([a] -> (Either Error b, [a]))
 
 instance Functor (Parser a)
@@ -18,6 +18,7 @@ instance Alternative (Parser a)
 instance toString Error
 
 runParser :: (Parser a b) [a] -> (Either Error b, [a])
+(<?>) :: (Parser a b) (String, Int) -> Parser a b
 fail :: Parser a b
 top :: Parser a a
 satisfy :: (a -> Bool) -> Parser a a
diff --git a/src/yard.icl b/src/yard.icl
index 5460312..278bac8 100644
--- a/src/yard.icl
+++ b/src/yard.icl
@@ -15,8 +15,8 @@ instance toString Error where
 	toString (LexError e) = "Lexer error: " +++ e
 
 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 +41,10 @@ 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
-- 
2.20.1