Re: [Haskell-cafe] Pointer equality for nullary constructors

Well, not always. They have special support in the RTS that seems worth experimenting with. setjmp/longjmp is what I'm after. On Feb 21, 2018 11:24 PM, "Branimir Maksimovic" < branimir.maksimovic@gmail.com> wrote:

Hm, isn't that exceptions are exceptional?

On 22.02.2018. 05:21, David Feuer wrote:

...

Because sometimes the sanctioned way is inefficient. throwIO always wraps its exception argument in a SomeException constructor before calling raiseIO# on the result. That extra baggage is likely enough to make the implementation I'm considering too slow to bother with, so I care right now in 2018. I'd very much prefer to get an officially-approved way to do what I want, but barring that I'll take one that works.

On Wed, Feb 21, 2018 at 9:33 AM, Doug McIlroy wrote:

...

Can I use reallyUnsafePtrEquality# reliably to identify whether a value

...

...

is

a nullary constructor of a particular type?

Can this "optimization" possibly save enough time to justify nonstandard trickery? This kind of obscure brittle coding may have been OK 50 years ago. But why do it now?

Doug _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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