[Haskell-cafe] Best way to format a number

[Maurí­cio]

Hi,

I would like to get a string for a number
using always 2 digits (i.e., 75 would be
"75", 3 would became "03"). What is the
best way to do that? I tried

printf "%02d\n" 3

which gives me the correct string, but
ghci always ends that call with a

*** Exception: Prelude.undefined

message. What else should I try? Can
Text.PrettyPrint do that?

Thanks,
Maurício