On 04/09/2014 13:25, p.k.f.holzensp...@utwente.nl wrote:
Dear Simon,
The point is to have
newtype Unique = Unique Int
Yes, I misunderstood, thanks!
where we use the boxing of Int, instead of creating our own boxing. Actually,
it seems useful to move to
newtype Unique = Unique Word
(see other discussions about unnecessary signedness).
I've been working on this (although only as a side-project, so progress is very
slow) and I've discovered a lot of API-out-of-sync-ness; there are comments
stating we don't export mkUnique, so that we can keep track of all the Chars we
use. Unfortunately, we *do* export mkUnique from Unique and we do *not* have
consistent use of Chars everywhere. I'm working to replace the Char-mechanism
with a (rather straightforward) sum-type UniqueDomain. This should also help
get a more consistent treatment of serialisation (the one in the module Unique
is *slightly* different from the one in BinIface).
I'm still not quite sure how to do the performance tests on the actual
compilation (i.e. runtime of GHC itself). If anything, moving Uniques to a
higher abstraction (coerced boxed values, instead of manually boxed stuff) is
actually a good litmus test of how far GHC's optimisations have come since '96
;)
If you have any more input, especially on performance stuff (what would be the
worst acceptable performance hit and measured on what, for example), it would
be *very* welcome!
There are compiler performance tests in testsuite/tests/perf/compiler.
They will only fail if the performance gets worse by 10% or so
(depending on the test), so instead of checking for failure just run the
tests manually and compare the allocation values before and after your
change (remember to save a copy of the original compiler binary so that
you can do comparisons).
Another way to test performance is to compile a large module, e.g.
nofib/spectral/simple/Main.hs is a good one.
Cheers,
Simon
Regards,
Philip
________________________________________
From: Simon Marlow <marlo...@gmail.com>
Sent: 04 September 2014 11:49
To: Edward Z. Yang; Holzenspies, P.K.F. (EWI)
Cc: ghc-devs
Subject: Re: Unique as special boxing type & hidden constructors
FastInt = Int#, so newtype doesn't work here.
Cheers,
Simon
On 15/08/2014 14:01, Edward Z. Yang wrote:
The definition dates back to 1996, so it seems plausible that
newtype is the way to go now.
Edward
Excerpts from p.k.f.holzenspies's message of 2014-08-15 11:52:47 +0100:
Dear all,
I'm working with Alan to instantiate everything for Data.Data, so that we can
do better SYB-traversals (which should also help newcomers significantly to get
into the GHC code base). Alan's looking at the AST types, I'm looking at the
basic types in the compiler.
Right now, I'm looking at Unique and two questions come up:
data Unique = MkUnique FastInt
1) As someone already commented: Is there a specific reason (other than
history) that this isn't simply a newtype around an Int? If we're boxing
anyway, we may as well use the default Int boxing and newtype-coerce to the
specific purpose of Unique, no?
2) As a general question for GHC hacking style; what is the reason for hiding
the constructors in the first place?
I understand about abstraction and there are reasons for hiding, but there's a
"public GHC API" and then there are all these modules that people can import at
their own peril. Nothing is guaranteed about their consistency from version to version of
GHC. I don't really see the point about hiding constructors (getting in the way of
automatically deriving things) and then giving extra functions like (in the case of
Unique):
getKeyFastInt (MkUnique x) = x
mkUniqueGrimily x = MkUnique (iUnbox x)
I would propose to just make Unique a newtype for an Int and making the
constructor visible.
Regards,
Philip
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