Re: [Haskell-cafe] Re: howto tuple fold to do n-ary cross product?

On Sun, Nov 30, 2008 at 11:04 AM, Larry Evans wrote:

The following post:

http://thread.gmane.org/gmane.comp.lib.boost.devel/182797

shows at least one person that would find it useful, at least in c++. Of course maybe it would be less useful in haskell.

The line: typedef boost::mpl::vector TT; Has the number of lists hard-coded as 3, and does not abstract over it. This corresponds to the "3" in "liftA3", or the number of <*>s in the expression. Abstracting over the number and types of arguments is something neither C++ nor Haskell is very good at. But in order to be able to do any abstraction using such a variable-argument function, the type systems of these languages would have to increase in complexity by quite a lot. Luke