Using "printf" on a list in Haskell

Question

How can i use printf over a list? I have a list of numbers and i want to print them all by respecting a format (ex: %.3f). I tried to use map over printf, but it does not work. So, i have no idea. Can somebody help me with this? Any ideas are acceptable. Is there a way to create a string from a list respecting a custom format?

can you please add what you tried - because I would indeed recommend using map and I don't see why it should not work — Random Dev
– Random Dev, Commented Apr 16, 2016 at 11:31
possible duplicate : stackoverflow.com/questions/36658890/… — Random Dev
– Random Dev, Commented Apr 16, 2016 at 11:33
the result of printf is polymorphic and can't be decided without context, try add more type signatures. — zakyggaps
– zakyggaps, Commented Apr 16, 2016 at 11:34
then please edit your question and add an answer or close/delete it - thanks — Random Dev
– Random Dev, Commented Apr 16, 2016 at 11:39

Mark Karpov · Accepted Answer · 2016-04-16 13:01:12Z

1

printf can produce strings instead of just printing them to stdout. This is because it is overloaded on its result type (it's also part of machinery that makes it variadic).

import Text.Printf

main :: IO ()
main = putStrLn . unwords $ printf "%.3f" <$> ([1..10] :: [Double])

That should do the trick.

BTW, printf is not type safe and can blow at run time. I recommend you use something like formatting.

edited Apr 16, 2016 at 13:01

answered Apr 16, 2016 at 11:43

Mark Karpov

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