On Mar 24, 2010, at 6:01 PM, 国平张 wrote:
Hi,
I wrote a type program to compute fibonacci series,
It certainly is possible to compute Fibonacci numbers as a "type program", but what you wrote is not a type program, just plain old Haskell.
if the max value is big, then it becomes very slow. like
take 100 fib
How can I make it faster :-)
Don't do it that way. Each element of your list is computed independently, and each computation takes exponential time (and would in C or Java). There are well known ways to compute Fibonacci numbers in linear and logarithmic time (assuming integer operations are constant time, which of course isn't true for big enough integers). They work well in Haskell too. The simplest thing -in Haskell- is to make the list element computations share the work using lazy evaluation. fibs :: [Integer] fibs = 1 : 1 : [x+y | (x,y) <- zip fibs (tail fibs)]