On Tuesday, February 5, 2002, at 02:16 , Jeffrey R Lewis wrote:
On Tuesday 05 February 2002 09:40 am, Brian Berns wrote:
I am new to functional programming and teaching myself Haskell. The canonical Haskell "fib" function (e.g. as presented in the "Gentle" tutorial) is:
fib = 1 : 1 : [ a+b | (a,b) <- zip fib (tail fib) ]
This seems, to be polite, a bit overly complex. By comparison, here is a simpler version:
As an aside, here's a nicer way of writing the stream version of fib:
fib = 1 : 1 : [ a + b | a <- fib | b <- tail fib ]
This gets rid of the distraction of the zip and the pair, letting you see the simple structure of the definition more clearly.
This, however, is not Haskell 98 (the use of multiple generators separated by `|'). But it is supported by both GHC and Hugs (using flag -98). See the sections in the user manuals under `parallel list comprehensions'.
And while you're at it start the sequence with 0 : 1 : ... so that it has the nice property that: gcd (fib !! m) (fib !! n) == fib !! (gcd m n) -- Frank Seaton Taylor fstaylo@alpha.ncsc.mil