Fergus Henderson wrote:
> On 19-Dec-1997, Simon L Peyton Jones <[EMAIL PROTECTED]> wrote:
> >
> > I thought you might find the following bug I've just
> > found in GHC entertaining.
...
> > sameVal (AbsApproxFun str1 v1) (AbsApproxFun str2 v2)
> > = str1 == str2 && sameVal v1 v1
...
> This bug could have been caught by a very simple static analysis that
> is very popular in the logic programming community: singleton variable
> warnings. In the code above, the variable `v2' occurs only once.
> Singleton variables such as this are often bugs. For cases where the
> programmer really does want a singleton variable, the warning can be
> suppressed by using a different naming convention (in Prolog, it
> would be `_v2'; since Haskell doesn't allow leading underscores,
> I suppose you could use `v2_').
In this case, the even simpler ``unused identifier'' warning would suffice!
(Easily suppressed by the use of a wildcard pattern such as `_'.)
> So, sing ho for regression tests, but sing louder for static analysis ;-)
Hear, hear!
Merry Xmas, etc.,
David Bruce
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