Lazy functors and friends

Henning Thielemann lemming at
Sun Jun 5 12:28:54 CEST 2011

I have written a Wiki article where I argue, that Functor instances
should match their arguments strictly in order to comply with the laws.
However for the Traversable class I did not find laws, thus I invented
one myself:

sequenceA (fmap Identity x)  ==  Identity x

What do you think of it? Are there more laws that would be reasonable?

More information about the Libraries mailing list