[Haskell-cafe] Best way to format a number

[Don Stewart]

briqueabraque:
> 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?
> 

It's to do with ghci's defaulting. This is fixed in ghc 6.8:

    Prelude Text.Printf> printf "%02d\n" 3
    03

You can work around it for now with:

    Prelude Text.Printf> printf "%02d\n" 3 >> return ()  
    03

-- Don