More work on parsing

Author: paf31

parsing.purs

@@ -34,9 +34,14 @@ fail message = Parser $ \s -> Left (parseError message)
 
 string :: String -> Parser String String
 string s = Parser $ \s' -> case indexOfS s' s of
-  0 -> Right $ parseResult (substr 0 (lengthS s) s') s
+  0 -> Right $ parseResult (substring (lengthS s) (lengthS s') s') s
   _ -> Left $ parseError $ "Expected \"" ++ s ++ "\""
 
+char :: Parser String String
+char = Parser $ \s -> case s of
+  "" -> Left $ parseError $ "Unexpected EOF"
+  _ -> Right $ parseResult (substring 1 (lengthS s) s) (substr 0 1 s)
+
 instance Prelude.Monad (Parser s) where
   return a = Parser $ \s -> Right (parseResult s a)
   (>>=) (Parser p) f = Parser $ \s -> case p s of

test.purs

@@ -7,10 +7,23 @@ import Parsing
 
 parser :: Parser String String
 parser = do
-  string "a" <|> string "b"
-  string "c" <|> string "d"
+  s1 <- string "a" <|> string "b"
+  s2 <- string s1
+  return $ s1 ++ s2
+
+parens :: forall a. ({} -> Parser String a) -> Parser String a
+parens p = do
+  string "("
+  a <- p {}
+  string ")"
+  return a
+
+nested :: {} -> Parser String Number
+nested _ = (do 
+  string "a"
+  return 0) <|> ((+) 1) <$> parens nested
 
 main = do
-  case runParser parser "ad" of
+  case runParser (nested {}) "(((a)))" of
     Left (ParseError err) -> Trace.print err.message
     Right (ParseResult res) -> Trace.print res.result