Re: Why are there no Show instances for internal types

My take is that we don't have these because they would slow down compilation times and add bloat. But enough people have asked for them (and, I can think of a few times when I would use them myself) that I think they should be added. It is conceivable that we could make the instances only when DEBUG is on. That would, I believe, involve some unsavory CPP, and may not be worth it. What do others think? Richard

On Mar 18, 2017, at 9:03 AM, Tom Sydney Kerckhove wrote:

Dear GHC Devs,

I am trying to use GHC as a library but I'm having a lot of trouble with understanding what everything means. Up to now, I have been able to figure out what to do by reading the sources, but it ocured to me that much of my struggles could have been mitigated if the relevant types had Show instances.

I am specifically talking about the types concerning type checking. TypecheckedModule and everything below that. I am aware that most of the types have an Outputable instance, but there are two problems with that:

- 'Outputting' a value requires DynFlags. (yes, I know about pprTrace) - These instances are not intended to show the internal structure of a value, but rather a 'human readable' representation of a value.

My questions for you:

- Is there a reason that there are no derived 'Show' instances for most types? - Would you accept a diff that adds these?

Thank you for your time.

-- Tom Sydney Kerckhove _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs