Lexing and parsing overhaul

1 files changed, 16 insertions, 3 deletions

diff --git a/DSL/BaseParsers.hs b/DSL/BaseParsers.hs
index 403ca42..b4b5234 100644
--- a/DSL/BaseParsers.hs
+++ b/DSL/BaseParsers.hs
@@ -69,6 +69,13 @@ infixl 3 `alt`
 alt :: Parser t a -> Parser t a -> Parser t a
 alt (Parser p) (Parser q) = Parser $ \ inp -> p inp <|> q inp
 
+chain :: Parser s [t] -> Parser t a -> Parser s a
+chain p q = do
+  ts <- p
+  case parse q ts of
+    Nothing     -> flunk
+    Just (_, x) -> result x
+
 -----------------------------------------------------------------------------
 
 phrase :: Parser t a -> Parser t a
@@ -77,8 +84,14 @@ phrase = (<* eof)
 recover :: a -> Parser t a -> Parser t a
 recover x p = p <|> pure x
 
-optional :: Parser t a -> Parser t (Maybe a)
-optional = recover Nothing . fmap Just
+optionalMaybe :: Parser t a -> Parser t (Maybe a)
+optionalMaybe = recover Nothing . fmap Just
+
+optionalEither :: e -> Parser t a -> Parser t (Either e a)
+optionalEither e = recover (Left e) . fmap Right
+
+optional :: Parser t a -> Parser t ()
+optional p = () <$ optionalMaybe p
 
 assert :: (a -> Bool) -> Parser t a -> Parser t a
 assert f p = do
@@ -108,7 +121,7 @@ atLeast :: Int -> Parser t a -> Parser t [a]
 atLeast i p = exactly i p <> mult p
 
 atMost :: Int -> Parser t a -> Parser t [a]
-atMost i = fmap catMaybes . exactly i . optional
+atMost i = fmap catMaybes . exactly i . optionalMaybe
 
 between :: Int -> Int -> Parser t a -> Parser t [a]
 between x y p = exactly (min x y) p <> atMost (abs $ x - y) p