Printf doesn't work? But it works in GHCi interactively.

Consider the trivial program

import Text.Printf
main = do
  printf "%f\n" pi
  return ()

When I put this into a file printf.hs and try to compile it (using GHCi or GHC) there is a type ambiguity that cannot be resolved using explicit casting of pi to Double. This is not different from examples that appear in Real World Haskell book. I also tried using "%g\n" instead of "%f\n".

On the other hand, this is what happens in GHCi interactively:

> pf1 = printf "%f\n" pi
> pf1
3.1415926535...

I'm using GHC v 10.8.4 under Windows.