diff --git a/Setup.hs b/Setup.hs
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+++ b/Setup.hs
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+module Main where
+import Distribution.Simple
+main = defaultMain
diff --git a/erf.cabal b/erf.cabal
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+++ b/erf.cabal
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+Name:		erf
+Version:	1.0.0.0
+License:	BSD3
+Author:		Lennart Augustsson
+Maintainer:	Lennart Augustsson
+Category:	Math
+Synopsis:	The error function, erf, and friends
+Stability:      experimental
+Build-type:	Simple
+Description:	A type class for the error function, erf, and related functions.
+		Instances for Float and Double.
+Hs-Source-Dirs: src
+Build-Depends:		base
+Exposed-modules:	Data.Number.Erf
diff --git a/src/Data/Number/Erf.hs b/src/Data/Number/Erf.hs
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+++ b/src/Data/Number/Erf.hs
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+{-# LANGUAGE ForeignFunctionInterface #-}
+module Data.Number.Erf(Erf(..)) where
+import Foreign.C
+
+foreign import ccall "erf" c_erf :: CDouble -> CDouble
+foreign import ccall "erfc" c_erfc :: CDouble -> CDouble
+foreign import ccall "erff" c_erff :: CFloat -> CFloat
+foreign import ccall "erfcf" c_erfcf :: CFloat -> CFloat
+
+-- |Error function related functions.
+--
+-- The derivative of 'erf' is @\ x -> 2 / sqrt pi * exp (x^2)@,
+-- and this uniquely determines 'erf' by @erf 0 = 0@.
+--
+-- Minimal complete definition is 'erfc' or 'normcdf'.
+class (Floating a) => Erf a where
+    erf :: a -> a
+    erfc :: a -> a       -- ^@erfc x = 1 - erf x@
+    erfcx :: a -> a      -- ^@erfcx x = exp (x*x) * erfc x@
+    normcdf :: a -> a    -- ^@normcdf x = erfc(-x / sqrt 2) / 2@
+
+    -- All the functions are inter-related, here's some defaults.
+    erf x = 1 - erfc x
+    erfc x = 2 * normcdf (-x * sqrt 2)
+    erfcx x = exp (x*x) * erfc x
+    normcdf x = erfc(-x / sqrt 2) / 2
+
+instance Erf Double where
+    erf = realToFrac . c_erf . realToFrac
+    erfc = realToFrac . c_erfc . realToFrac
+
+instance Erf Float where
+    erf = realToFrac . c_erff . realToFrac
+    erfc = realToFrac . c_erfcf . realToFrac