I think that's a good risk to be aware of. One nice thing about the
architecture under discussion, though, is that it shares much more
code than the previous design. I wasn't a previous user of External
Core, but it seems to me that it was allowed to bit-rot in part
because it duplicated many things that existed elsewhere in the
compiler (for instance, a data type representing types), which then
became outdated when the main compiler data structures changed (such
as when FC was introduced).
In Simon's proposed design, the HsType data type, for instance, is
shared between Haskell and External Core, which makes sense because
the two languages have a very similar type structure. However, since
they have very different term structures, there would be distinct
HsExpr and ExtCoreExpr data types. It would be very hairy, in just
the way you're describing, if we used HsExpr to represent
ExtCoreExpr, since HsExpr is such a richer language. Checking that an
instance of HsExpr is valid External Core would be quite a pain.
Checking that an HsType is valid for Exernal Core, however, seems
like it should be pretty easy.
I could easily be missing some complications, though. I'm open to
further suggestions.
Aaron
On Dec 6, 2006, at 6:45 AM, Kirsten Chevalier wrote:
Message: 4
Date: Tue, 5 Dec 2006 16:00:28 +0000
From: Simon Peyton-Jones <[EMAIL PROTECTED]>
Subject: RE: Replacing Ty in ExternalCore with IfaceType
To: Aaron Tomb <[EMAIL PROTECTED]>, "[EMAIL PROTECTED]"
<[EMAIL PROTECTED]>
Message-ID:
[snip]
* Be careful to specify the sub-language of HsSyn that is ExtCore
This seems like asking for trouble, too, although I guess it depends
on what you mean by "be careful" and "specify". I can imagine bugs
potentially sneaking in when somebody makes a change to GHC without
thinking about ExtCore (which is exactly what happened in the past),
but I suppose that it's possible to implement some sort of
ext-core-lint phase or something that checks that the ExtCore that GHC
is generating is consistent with the specification. But, you would
want to make sure that that phase was actually enabled when the test
suite gets run.
Cheers,
Kirsten
--
Kirsten Chevalier* [EMAIL PROTECTED] *Often in error,
never in doubt
"It ain't no hassle, it ain't no mess / Right now it's the only
power that I
possess / these businessmen got their money, they got their
instruments of
death / but I can make life, I can make breath" -- Ani DiFranco
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