According to https://hackage.haskell.org/package/base-4.10.0.0/docs/Text-Printf.html#g:2, you only need to implement `PrintfArg`. There is also an example for `()`.

Baa <aquagnu@gmail.com> schrieb am Fr., 24. Nov. 2017 um 13:33 Uhr:
Hello All!

As I understand to use Text.Printf.printf with custom types or to
return result as Text instead of String I must implement some
class instances: PrintfType, PrintfArg. But how to do this if they are
exported from module as type-names only - without its methods (i.e. not
"Printf (..)", but "Printf") ?

I tried to import Text.Printf.Internal but seems that no such
submodule...

Any ideas?

===
Best regards, Paul
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