On Thu, 19 Oct 2006, Mikael Johansson wrote:
Comparing the code for permutationgropus at
http://www.polyomino.f2s.com/david/haskell/codeindex.html
with my own thoughts on the matter, I discover the one line to figure out
whether a specific list represents the identity:
isIdentity (PL xs) = all (\(i,j) -> i==j) (zip [1..] xs)
Is there any sort of benefit to be won by using this construction instead of
isIdentity (PL xs) = xs == [1..(length xs)]
and if so, what?
At some point in the future, I'll learn to think more before I post. Say
isIdentity xs = all (\(i,j) -> i==j) (zip [1..] xs)
isIdentity' xs = xs == [1..(length xs)]
Then
isIdentity 1:3:2:[4..100000]
finishes in an instant, whereas
isIdentity' 1:3:2:[4..100000]
takes noticable time before completing.
So it's a question of getting laziness to work for you.
--
Mikael Johansson | To see the world in a grain of sand
[EMAIL PROTECTED] | And heaven in a wild flower
http://www.mikael.johanssons.org | To hold infinity in the palm of your hand
| And eternity for an hour
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