[Haskell-cafe] Deciding equality of functions.

[Vo Minh Thu]

2011/4/9 Grigory Sarnitskiy <sargrigory at ya.ru>:
> I guess that deciding whether two functions are equal in most cases is algorithmically impossible. However maybe there exists quite a large domain of decidable cases? If so, how can I employ that in Haskell?
>
> It is a common situation when one has two implementations of the same function, one being straightforward but slow, and the other being fast but complex. It would be nice to be able to check if these two versions are equal to catch bugs in the more complex implementation.

Hi,

Instead a trying to decide if they are equal, I would simply go
through a well-known route:

Pick the simple implementation and test toroughly, to see if it is
'correct' w.r.t. some specification. This involves things like unit
tests and QuickCheck. Then apply those those tests to the second
implementation once you're satified with the results of the first one.

This transforms your problem of deciding if two functions are equal
into trusting enough your two functions given some tests.

Cheers,
Thu