You can convert a floating-point number to an Int or Integer using truncate and round. Idiom #80 Truncate floating point number to integer. We’ve gone over some of the conversions between similar types. Because Haskell has more than one type of floating point numbers, this "more generic" The usual way to convert an Int to a Double is to use fromIntegral, which has the type (Integral a, Num b) => a -> b. ... (Fractional a) => Floating a where ... truncate x yields the integer nearest x between 0 and x, inclusive. The Haskell Prelude contains predefined classes, types, and functions that are implicitly imported into every Haskell program. Haskell has two main floating point types: Float and Double. Make sure to truncate towards zero: a negative x must yield the closest greater integer (not lesser). Instead of using the methods from RealFrac I could simply use double2Int but I consider this a work-around. You can also see this by calculating 0.1 + 0.2, which awkwardly returns 0.30000000000000004 instead of 0.3. As far as I can judge, double2Int does the same like truncate. round x returns the nearest integer to x, the even integer if x is equidistant between two integers. Haskell/Type basics II, Float' instance Floating Double -- Defined in 'GHC. sumU . We can see this effect in practice in any language that supports floating point, such as Haskell: > truncate (16777216 - 1 :: Float) 16777215 > truncate (16777216 + 1 :: Float) 16777216 Subtracting 1 gives us the decremented number, but adding 1 had no effect with floating point math! Conversion Mania. You can convert an Integer to a floating-point number (Float or Double) using fromInteger. instance Enum Float where succ x = x + 1 pred x = x-1 toEnum = int2Float fromEnum = fromInteger. A Tour of the Haskell Prelude (and a few other basic functions) Authors: Bernie Pope (original content), Arjan van IJzendoorn (HTML-isation and updates), Clem Baker-Finch (updated for Haskell 98 hierarchical libraries organisation). mapU (floor :: Double -> Int) $ enumFromToFracU 0 100000000 Runs in 1 minute, 10 seconds: $ time ./henning 5000000050000000 ./henning 70.25s … main = print . The Float type is a single-precision floating point number. To make searching easy I've included a list of functions below. So now, we *do* have a good rule for truncate, but floor, ceiling and round turn out to be awesomely slow. But it’s difficult to keep track of all the different ways to convert between values. This isn't a haskell problem as much as a floating point problem. As to GHC. The function properFraction takes a real fractional number x and returns a pair (n,f) such that x = n+f, and: . n is an integral number with the same sign as x; and ; f is a fraction with the same type and sign as x, and with absolute value less than 1.; The default definitions of the ceiling, floor, truncate and round functions are in terms of properFraction. Trac metadata See Float… @chi, ceiling, floor, truncate and fromIntegral are mentioned in the answer, so not quite sure why you brought them up. Since each floating point number is implemented in a finite number of bits, there exist numbers that can't be represented completely accurately. Float. This webpage is a HTML version of most of Bernie Pope's paper A Tour of the Haskell Prelude. And of course, ... round, truncate, and so on. Problem Solution Examples creating a complex number from real and imaginary rectangular components Values of the built-in type Float are floating-point numbers: Main> 10 / 2.4 4.16667. 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