How to get a decimal string from a Double instead of scientific notation in Haskell?

Question

I need to divide a list of numbers by 100 to be printed, for example:

map (/100) [29, 3, 12]

produces:

[0.29,3.0e-2,0.12]

however I need:

[0.29,0.03,0.12]

How do I do this in Haskell? Any ideas really appreciated.

Answer 1

0.03 and 3.0e-2 are the same number. Internally, GHC uses showFloat to print it, which will result in the scientific notation whenever the absolute value is outside the range 0.1 and 9,999,999.

Therfore, you have to print the values yourself, for example with printf from Text.Printf or showFFloat from Numeric:

import Numeric

showFullPrecision :: Double -> String
showFullPrecision x = showFFloat Nothing x ""

main = putStrLn (showFullPrecision 0.03)

Depending on your desired output, you need to write some more functions.

Answer 2

What works for me is: cabal install numbers and then in GHCi

λ: import Data.Number.CReal
λ: map (/(100 :: CReal)) [29,3,12]
[0.29,0.03,0.12]