Where is fromRealFrac?

Question

Where can I find the fromRealFrac function? According to the gentle intro the function should exist and from a bit of googling around, I gather it should be in Prelude - yet ghci complains that it's not in scope.

I'm using fromRational . toRational for the time being, as according to the gentle intro that's how fromRealFrac is meant to be defined.

Answer 1

The function formerly known as "fromRealFrac" was renamed "realToFrac" in the Haskell 98 Report.

In the Haskell 1.4 Prelude we find

fromRealFrac    :: (RealFrac a, Fractional b) => a -> b
fromRealFrac    =  fromRational . toRational

However, by Haskell 98 it is known as

realToFrac     :: (Real a, Fractional b) => a -> b
realToFrac      =  fromRational . toRational

This change is listed in the Haskell 98 Report Errata:

[Apr 2001] Page 84, Section 6.4, Fig 7; and bottom of page 86, Section 6.4.6.
    fromRealFrac :: (RealFrac a, Fractional b) => a -> b
should be replaced by
    realToFrac :: (Real a, Fractional b) => a -> b

The closest commit I could find was this in the report repo.

Answer 2

It appears this function is called realToFrac in the GHC Prelude.