Pretty-print anything

[guibou]

In PyF we have the {expr:s} or {expr} which converts to string. But it would be nice to have something like python !r to force the conversion to a "repr" format, which should work for any type.

What could be a "repr" format? Well, we could use Generic or Data to derive a generic view of the internal of the structure.

[guibou]

Rust does pretty printing / debug with #?.

[michaelpj]

Could try https://hackage.haskell.org/package/recover-rtti ?