Re: [Haskell-cafe] Questions about the Functor class and it's use in "Data types à la carte"

Yitzchak Gale wrote:

When using seq and _|_ in the context of categories, keep in mind that Haskell "composition" (.) is not really composition in the category-theoretic sense, because it adds extra laziness. Use this instead:

(.!) f g x = f `seq` g `seq` f (g x)

id .! undefined == \x -> undefined /= undefined Probably you meant (.!) f g = f `seq` g `seq` (f . g) Zun.