[Haskell-cafe] Pointer equality for nullary constructors

[David Feuer]

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 <doug at cs.dartmouth.edu> 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
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