Removing -fext-core

Simon Peyton Jones simonpj at
Mon Apr 28 09:09:04 UTC 2014

In principle I think it's a pity to lose External Core.  It provides an interface to GHC that is based on the simplest possibly connector (a text file), and allows GHC's front end or back end to be used by other systems written in different languages.

However, as you say, it has received no love for many years. I have repeatedly sought someone to support and maintain External Core, but no one has stepped forward.  That doesn't mean that no one is using it!  But the absence of bug reports, given how much it has bit-rotted, is a strong indicator that no one is.

So I'd like hear from our users, but I won't stand in the way of removing it.


| -----Original Message-----
| From: Glasgow-haskell-users [mailto:glasgow-haskell-users-
| bounces at] On Behalf Of Austin Seipp
| Sent: 27 April 2014 14:14
| To: ghc-devs at; glasgow-haskell-users at
| Subject: Removing -fext-core
| Hello all,
| Recently I was wondering something: is there any reason to keep -fext-
| core around? In particular, it's been broken for a while at this point,
| see GHC bug #5630[1]
| As far as I'm aware there really aren't any users of it still around
| these days, at least none working with a modern GHC. And it seems like
| if people were to need access to Core, they could use a plugin or some
| such to get direct access to what they want.
| Simon mentioned removing ExtCore in face of replacing it with IfaceSyn
| in the compiler. I'm not entirely sure how much work that would be to
| bring it all up to scratch if people needed it, but maybe it's worth
| thinking about.
| One other issue is a notion of semantics which is present in External
| Core, but we also now have a documented semantics for GHC's core
| language as well (which has evolved quite a bit), so I don't know how
| much that matters.
| So long story short: I don't think anyone is using it, maintaining it,
| and it seems subsumed by more recent events.
| Therefore, if nobody objects, I'd vote to remove -fext-core from GHC,
| unless someone is willing to step up and really maintain it. If you're
| using it, you should probably speak up soon I'd imagine...
| [1]
| --
| Regards,
| Austin Seipp, Haskell Consultant
| Well-Typed LLP,
| _______________________________________________
| Glasgow-haskell-users mailing list
| Glasgow-haskell-users at

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