>> With
>> functional languages you need only test that your function returns the
>> correct value.  If it does, your function is correct and should always be
>> correct.

> Well, that's a very broad statement, and one that you cannot defend in
> general. Consider the purely functional code below:

> double bar()
> {
>     return log(foo());
> }

> Here, your implementation depends on foo() not returning anything less
> than or equal to zero. Checking the return value is not going to make
> this any better because if foo() returns something less than zero it
> doesn't even make sense to produce any value. The point here is that
> this code, which is completely independent of foo(), places an
> implicit constraint on foo(), or is dependent on an implicit
> constraint of foo(). This is similar to code depending on the state of
> an object in an OO language.