[Haskell-beginners] How to use Text.Printf w/ custom types

[Norbert Melzer]

PrintfArg does not have toUPrint. The functions in there are formatArg and
parseFormat.

PrintfType is according to its documentation, an interface that you shall
not implement yourself.

Baa <aquagnu at gmail.com> schrieb am Fr., 24. Nov. 2017 um 15:08 Uhr:

> I talked about PrintfType and its method `hspr`.
>
> With PrintfArgs the same problem:
>
>   instance PrintfArg JobEvent where
>     toUPrintf _ = UString "aaa"
>
>       ^^^ toUPrintf is not visible ERROR here...
>
> Header of this file looks like:
>
>   module Text.Printf(
>      printf, hPrintf,
>      PrintfType, HPrintfType, PrintfArg, IsChar
>   ) where
>
> so methods are not exported? And I don't see any Internal subpackage...
> OK, no problem, I switched already to very cool `formatting` library :)
>
> Thanks a lot!
>
>
> > It appears PrintfArg and its methods are fully exported.
> >
> > On Fri, Nov 24, 2017 at 8:19 AM, Baa <aquagnu at gmail.com> wrote:
> >
> > > But how to do it if "methods" are not exporting?
> > >
> > > > 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 at 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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