Re: [Haskell-cafe] List comparisons and permutation group code

On 19/10/06, Brandon Moore wrote:

isIdentity xs = xs == takeLengthOf xs [1..] where takeLengthOf xs ys = zipWith const ys xs

You probably mean zipWith (flip const) xs ys.

for finite lists, takeLengthOf xs ys == take (length xs) ys

This ruins the laziness again: Hugs.Base> let takeLengthOf xs ys = take (length xs) ys; isIdentity xs = xs == takeLengthOf xs [1..] in isIdentity (1:3:2:[4..10000]) False (210064 reductions, 278075 cells) Hugs.Base> let takeLengthOf = zipWith (flip const); isIdentity xs = xs == takeLengthOf xs [1..] in isIdentity (1:3:2:[4..1000]) False (60 reductions, 114 cells) -- -David House, dmhouse@gmail.com