[Haskell-cafe] New (simple) Lazy Evaluation tutorial

Seth Gordon sethg at ropine.com
Thu Jan 18 16:43:07 EST 2007

Andrew Wagner wrote:
> Hi all,
> An interesting question came up in #haskell the other day, and I took
> the resulting discussion and wrapped it up into a simple tutorial for
> the wiki. Since I'm quite a newbie to haskell myself, I'd appreciate
> any double-checking of my logic and, of course, any other
> comments/suggestions. Thanks to Cale for his efforts on this problem,
> and to the original asker, whose name I can't recall.
> http://www.haskell.org/haskellwiki/Haskell/Lazy_Evaluation

Rather than use the Fibonacci series as an example, why not something
like this...?

contains :: String -> String -> Bool
contains _ "" = False
contains "" _ = True
contains (x:xs) (y:ys) =
    ((x == y && contains xs ys) || contains (x:xs) ys)

infiniteBanana :: String
infiniteBanana = "banana" ++ infiniteBanana

contains "na" infiniteBanana

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