Output with precision 5

app/Main.hs

@@ -2,16 +2,31 @@ module Main (main) where
 
 import Text.Parsec
 
-import Lib (exprparser, evaluate)
+import Lib (exprparser, evaluate, replaceVars)
+
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Data.Ratio
 
 import System.IO
 
 main :: IO ()
 main = ioLoop
 
-useResult (Right e) = show . evaluate $ e
+precision = 5 :: Int
+
+showRatio :: Int -> Rational -> String
+showRatio p r = (if (r < 0) then "-" else "") ++ prepoint_digits ++ "." ++ postpoint_digits
+    where
+    	prepoint_digits  = init . show . round $ (r * 10)
+	postpoint_digits = (take p) . (drop (length prepoint_digits)) . show . round $ (r * 10^p)
+
+useResult (Right e) = (showRatio precision) . evaluate $ replaceVars e vars
 useResult (Left  e) = show e
 
+vars :: Map String Rational
+vars = Map.fromList [("pi", 245850922 % 78256779), ("e", 271801 % 99990)]
+
 ioLoop :: IO ()
 ioLoop = do done <- isEOF
             if done