Things stopping pure Haskell code from having a cross-platform single semantics?
Haskell isn't like Java byte code in having a single semantics for a program irrespective of where it is run. In particular, "Int" has a platform-defined width -- so the same (pure) code can yield different answers on different machines. numCapabilities was also a "leak" of platform information, which did not require IO. But, happily, now it does not appear in the [Trustworthy] module, Control.Concurrent. Ok, what else? What other holes are there that allow my pure functions to change their answer on different machines? I'm making a list of these in a paper and I want to make sure I give a full account. Thanks, -Ryan
On Mon, Nov 11, 2013 at 10:01 AM, Ryan Newton
Ok, what else? What other holes are there that allow my pure functions to change their answer on different machines? I'm making a list of these in a paper and I want to make sure I give a full account.
Not something likely to strike the average program, but all the CAFs in System.Info are pure (not in IO). And two of them claim to be *runtime* information. :( -- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net
For a few more such leaks, see
http://hackage.haskell.org/package/base-4.6.0.1/docs/System-Info.html , as
mentioned in http://conal.net/blog/posts/notions-of-purity-in-haskell . --
Conal
On Mon, Nov 11, 2013 at 7:01 AM, Ryan Newton
Haskell isn't like Java byte code in having a single semantics for a program irrespective of where it is run. In particular, "Int" has a platform-defined width -- so the same (pure) code can yield different answers on different machines.
numCapabilities was also a "leak" of platform information, which did not require IO. But, happily, now it does not appear in the [Trustworthy] module, Control.Concurrent.
Ok, what else? What other holes are there that allow my pure functions to change their answer on different machines? I'm making a list of these in a paper and I want to make sure I give a full account.
Thanks, -Ryan
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The pure functions from Data.Char depend on the system locale, at least with GHC's implementation.
participants (4)
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Brandon Allbery -
Conal Elliott -
Niklas Haas -
Ryan Newton