On Wed, Feb 18, 2004 at 01:58:58AM +0000, Matthew Vogt wrote:
Couple of questions:
What are the features of fcpp::lambda that monads depend on, that boost::lambda does not provide?
Well, technically you don't even need lambda to implement monads. But to do monads well/easily, you need syntax sugar (along the lines of Haskell's "do" notation or FC++'s comprehensions). This sugar requires explicit lambda variables (the same kind you see in FC++ lambda's let/letrec). It's unclear to me if/how to do that with (or extend) boost::lambda in a natural way to get this. You also need to nest lambdas more often with monads. This is easier to do with explicit lambda (like FC++) than with boost::lambda (which has "protect" to help with this). There are also nits, like FC++'s letrec and if1/if2, which have come in handy in the implementation of certain monad functions, for various obscure reasons. This is a pretty rambling and vague-sounding answer, I suppose, hrm.
Are these features not able to be implemented in boost::lambda (given the current design), if that were desirable?
I think they don't "mesh well" with boost::lambda's design. While "anything's possible", my impression is that it's hard to design one tool that is as good at doing what boost::lambda does well and is simultaneously also good at doing monads; in a single design incorporating both, one or the other has to "suffer" a bit. -- -Brian McNamara (lorgon@cc.gatech.edu)