[Haskell-cafe] Re: Need some help with an infinite list
haskell at brecknell.org
Sat Jun 20 23:46:31 EDT 2009
Thomas Hartman wrote:
> could someone explain sharing?
A good tool for visualising the difference between shared and non-shared
results would be vacuum, using one of its front ends, vacuum-cairo or
To see sharing, you will need to view a set of outputs (not just one
string). To keep the graph to a manageable size, use a smaller alphabet:
digits = "01"
-- All words of length n, with shared substrings
shared :: Int -> [String]
shared n = sss !! n where
sss = [""] : [ [ c:s | c <- digits, s <- ss ] | ss <- sss ]
-- All words of length n, with unshared substrings
unshared :: Int -> [String]
unshared 0 = [""]
unshared n = [ c:s | c <- digits, s <- unshared (n-1) ]
And then in GHCi:
Vacuum.Cairo> shared 3 == unshared 3
Vacuum.Cairo> view $ shared 3
Vacuum.Cairo> view $ unshared 3
I'd send some PNGs, except my vacuum installation is currently broken.
Perhaps someone else can?
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