Using the "bind" operator

[my-scheme.git] / app / Main.hs

diff --git a/app/Main.hs b/app/Main.hs
index c64fd18d83b0cdf0575889388df8cfa6344619c8..88ae7f7ff2ff0b439dcb452d24c2be9a66e55e41 100644 (file)
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -1,4 +1,5 @@
 module Main where
+import Control.Monad
 import Text.ParserCombinators.Parsec hiding (spaces)
 import System.Environment
 
@@ -15,8 +16,35 @@ symbol = oneOf "!#$%&|*+-/:<=>?@^_~"
 spaces :: Parser ()
 spaces = skipMany space
 
+parseString :: Parser LispVal
+parseString = do
+    char '"'
+    x <- many (noneOf "\"")
+    char '"'
+    return $ String x
+
+parseAtom :: Parser LispVal
+parseAtom = do
+    a <- letter <|> symbol
+    b <- many (letter <|> digit <|> symbol)
+    let atom = a:b
+    return $ case atom of
+                "#t" -> Bool True
+                "#f" -> Bool False
+                _    -> Atom atom
+
+parseNumber :: Parser LispVal
+parseNumber = many1 digit >>= \ ds ->
+              let a = read ds
+              in return $ Number a
+
+parseExpr :: Parser LispVal
+parseExpr = parseString
+        <|> parseAtom
+        <|> parseNumber
+
 readExpr :: String -> String
-readExpr input = case parse (spaces >> symbol) "lisp" input of
+readExpr input = case parse parseExpr "lisp" input of
     Left err -> "No match: " ++ show err
     Right val -> "Found value"