Hi Peter, 2007/6/25, peterv <[EMAIL PROTECTED]>:
I'm baffled. So using the Arrow abstraction (which I don't know yet) would solve this problem? How can (perfectActionB x) be checked with without ever executing performActionA which evaluates to x? This can only be done when x is a constant expression no?
Arrows separate the action -- 'performActionB' -- from the argument -- 'x', so you can look at the action before you have to compute the argument to it. Of course, this means that you can no longer compute the action from the argument -- that is, 'if x then performActionB else performActionC' is something you can't directly do; you have to use a choice primitive instead, which explicitly says "use one of these two arrows depending on what value this argument is," which then lets the library check these two arrows before actually applying them to an argument. - Benja _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
