At 10:41 AM 6/8/2001 -0400, S. Alexander Jacobson wrote:
One portable way to implement a memoizing function in Haskell (if the domain of the function is countable) is to lazily build a data structure that contains the results of the function on every possible argument. Then you evaluate the portions of the data structure that you need; the result on each argument is only evaluated once. This probably would count as a "growing expression", and it's certainly possible that the function on some arguments would be bottom.
I don't think I understood this. Can you clarify?
I believe I know what he's talking about. The example I've read about this technique is random-number generators. Because typical generators will need a state (the seed), they can be awkward to use in functional languages. Instead, you can just generate an infinite list of the random numbers, and extract them from that list lazily. Specifically, what he's talking about is the fact that a function like "Natural -> a" corresponds to a list where all the possible results for each number are stored in the corresponding position in the list. If you generate that list lazily, and then access it, each element will only be computed once (the compiler/interpreter takes care of this in a very natural way). But if you do this, the program will (or can) grow as more elements get computed. Am I making sense? Salutaciones, JCAB --------------------------------------------------------------------- Juan Carlos "JCAB" Arevalo Baeza | http://www.roningames.com Senior Technology programmer | mailto:jcab@roningames.com Ronin Entertainment | ICQ: 10913692 (my opinions are only mine) JCAB's Rumblings: http://www.metro.net/jcab/Rumblings/html/index.html