haskell - Formatting a list of doubles into a string -


i trying format list of doubles string. turn list such as:

[0.38, 0.94]

into like:

"astring 0.380  0.940"

i have tried:

"astring" ++ map (printf "%7.3f") [0.38, 0.94]

and feedback:

<interactive>:80:19:     no instance (printftype char)       arising use of `printf'     possible fix: add instance declaration (printftype char)     in first argument of `map', namely `(printf "%7.3f")'     in second argument of `(++)', namely       `map (printf "%7.3f") [0.38, 0.94]'     in expression: "astring" ++ map (printf "%7.3f") [0.38, 0.94]

i've not been able fix this. have unable compose signature works.

thank you

the problem map (printf "%7.3f") [0.38, 0.94] of type [string], not string. use concatmap:

prelude text.printf> "astring" ++ concatmap (printf "%7.3f") [0.38, 0.94] "astring  0.380  0.940"

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