GHCi, version 6.10.1 crashes without message
Roman Cheplyaka
roma at ro-che.info
Tue Jan 13 15:17:24 EST 2009
* Heiko Studt <studt at fmi.uni-passau.de> [2009-01-13 16:15:51+0100]
> Hi (and hello everybody),
>
> I read the FAQ, I searched down till Nov 2008, but did not find anything.
> I hope I didn't miss a FAQ or somewhat. (If so, please apologize!)
>
> My (freshly installed) GHCi 6.10.1 runs on Windows XP on Intel Dual Core.
> I used the .msi of the Webpage some two weeks ago.
>
> I got some strange program as example and tried out - and my ghci died
> quitly without any helping message.
>
> Here is the original programm:
> | f x y z = a + b*c + b + fun c
> | where a = x * y + z
> | b = c * fun x
> | c = a * b
> | fun x = x * x + 1
>
> For testing out in previous of this posting, the following is the very
> same and had the same problem:
> | let f x y z = a + b*c + b + fun c where {a = x * y + z; b = c * fun x; c = a * b; fun x = x * x + 1}
>
> The query to die was "f 1 2 3".
[...]
Your program loops for the following reason:
to compute f, you need to compute c
to compute c, you need to compute b
to compute b, you need to compute c again!
Haskell cannot solve equations (or, at least, not formulated in this
way), so it understands definition of f as the rules to compute things
like a, b, c. No wonder evaluation of f never terminates.
--
Roman I. Cheplyaka :: http://ro-che.info/
"Don't let school get in the way of your education." - Mark Twain
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