Bugfix for QuickCheck 220.127.116.11
patperry at stanford.edu
Tue Sep 2 01:36:27 EDT 2008
First, the version of variant I gave will behave reasonably if given a
negative argument, so the overflow is not catastrophic.
Second, I'm not sure what you mean by a "simple" generator. Let's
consider Int instead of Double. With the current version of variant,
"coarbitrary 1" calls split one time, and "coarbitrary 1000" calls
split 1000 times. At the end of the day, though, all random number
generators are equally "complex". The only difference is that they
have different seeds.
You are correct the QuickCheck2 uses "toRational" instead of
"decodeFlloat" for the coarbitrary instance. I don't think it matters
either way which one gets used, though, and I would rather change as
little code as possible in QuickCheck1.
Jed Brown wrote:
> I haven't looked at this in a while but I'm not sure this completely
> fixes things with regard to coarbitrary. That is, we can produce very
> simple Doubles (as defined by arbitrary) that produce (via
> very complicated generators for other types (and there was an issue of
> overflow with possible sign change due to nasty casting, hence variant
> getting a negative argument). As I understand it, your fix to variant
> means that variant will return in a reasonable amount of time even
> a huge argument, but it doesn't fix the issue that coarbitrary should
> produce a `simple' generator for a `simple' argument. I thought QC2
> a mechanism to fix this.
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