what's the deal with "user error" on fail?
jcast at cate0-46.reshall.ou.edu
Thu Nov 13 19:37:25 EST 2003
David Roundy <droundy at abridgegame.org> wrote:
> well that's because haskell is not as pure as it claims to be :-)
Nonsense. Haskell is perfectly pure; the IO monad is just
> if every monad supports errors depends on what you mean by "supporting
I mean `supporting errors' in the only possible sense that `supporting
errors' can be implied by the existence of `fail': we have a throw
> i would argue that supporting errors and divergence is not the same
I never said it was.
> the difference is that one should be able to handle an error thrown by
> a computation,
Although this doesn't imply the existence of a `catch' HOF; see the
MonadPlus instance for Maybe.
> while clearly we cannot detect nonterminating computations.
Of course. But we can detect exceptions thrown by `error'. Even though
we can't distinguish them from non-termination /in pure Haskell/. We
can of course distinguish them in the IO monad (which perhaps ought to
be re-named the SinBin monad, to be more honest...). So we can detect
erroneous computations in any monad.
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