exercise 3: parse SExpr

diff --git a/hw11/SExpr.hs b/hw11/SExpr.hs
index b70683a583a4275278ab6d416eee9b78f7d12795..15d6f6f9e53d8927650d6b2e92483c5250d9942e 100644 (file)
--- a/hw11/SExpr.hs
+++ b/hw11/SExpr.hs
@@ -52,3 +52,13 @@ data Atom = N Integer | I Ident
 data SExpr = A Atom
            | Comb [SExpr]
   deriving Show
+
+parseAtom :: Parser Atom
+parseAtom = spaces *> (N <$> posInt <|>
+                       I <$> ident) <* spaces
+
+parseSExpr :: Parser SExpr
+parseSExpr = A <$> parseAtom <|>
+             Comb <$> parseComb
+  where
+    parseComb =  spaces *> char '(' *> oneOrMore parseSExpr <* spaces <* char ')' <* spaces