types: drop in replacement of double to 90 decimal bigfloat

bc.cabal

@@ -14,6 +14,6 @@ cabal-version:       >=1.10
 executable bc
   main-is:             Main.hs
   hs-source-dirs:      src/
-  build-depends:       base >=4.9 && <4.10, directory, hashmap, parsec, unix
+  build-depends:       base >=4.9 && <4.10, directory, hashmap, numbers, parsec, unix
   hs-source-dirs:      src
   default-language:    Haskell2010

src/BC/Parse.hs

@@ -32,8 +32,10 @@ float = do
     _ <- P.string "."
     y <- P.many1 P.digit
     case neg of
-      Just "-" -> (return . BNum . BFloat . read) ("-" ++ x ++ "." ++ y)
+      Just "-" -> return $ construct ("-" ++ x ++ "." ++ y)
-      _        -> (return . BNum . BFloat . read) (x ++ "." ++ y)
+      _        -> return $ construct (x ++ "." ++ y)
+        -- do a little dance
+  where construct str = BNum $ BFloat $ fromRational $ realToFrac $ (read str::Double)
 
 
 integer :: P.Parser Value

src/BC/Types.hs

@@ -1,6 +1,7 @@
 module BC.Types where
 
 import Data.List (intercalate)
+import Data.Number.BigFloat
 
 data Value = BNum Number
            | BBool Bool
@@ -36,7 +37,7 @@ instance Show Value where
 
 -- sorry, this is a little hacky
 data Number = BInt Integer
-            | BFloat Double
+            | BFloat (BigFloat (PrecPlus20 (PrecPlus20 Prec50)))
   deriving (Ord, Eq)
 instance Show Number where
   show (BInt i) = show i