From: Ramakrishnan Muthukrishnan <ram@rkrishnan.org>
Date: Sun, 28 Dec 2014 10:54:58 +0000 (+0530)
Subject: exercise 3: parse SExpr
X-Git-Url: https://git.rkrishnan.org/pf/content/en/seg/frontends/quickstart.html?a=commitdiff_plain;h=03f5b2992dea2e5c21df8af1292d516899cf0f3b;p=yorgey.git

exercise 3: parse SExpr
---

diff --git a/hw11/SExpr.hs b/hw11/SExpr.hs
index b70683a..15d6f6f 100644
--- 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