Adding name to not implemented placeholder errors

[sordina]

It's nice to see what isn't implemented when you get an error.

When you use the define action on undefined names, you get something like this:

step :: Generation -> Generation
step = error "not implemented"

But wouldn't it be nicer to see this?

step :: Generation -> Generation
step = error "step not implemented"

[pepeiborra]

Actually, I would prefer if the body of the unimplemented function was just a hole:

step :: Generation -> Generation
step = _

Could you change it to that instead?

[sordina]

@pepeiborra Sure! My workflow actually depends on hitting the errors, so I'm guessing there's a 'defer-holes' kind of option to allow running. (Edit: Confirmed as -fdefer-typed-holes)

[pepeiborra]

Thank you!
Couple of tests need to be updated, but otherwise it looks good to me.

[sordina]

@pepeiborra having some issues running the tests right now. I'll come back to this soon.

[Anton-Latukha]

Yep, consistently getting the test error.

[pepeiborra]

This is already fixed in #2740