[Haskell-cafe] Text search
Scott & Kathy
turners at billygoat.org
Mon May 16 09:33:00 EDT 2005
On 2005 May 16 Monday 08:00, Gracjan Polak wrote:
> Ketil Malde wrote:
> > While the result isn't exactly the same, I suspect
> > using isPrefixOf and tails would be more efficient.
> I need the data before and including my needle.
When the haystack gets large, the beautiful
find (isSuffixOf "needle") (inits "haystack")
is quite inefficient where it uses isSuffixOf searching longer and longer
You can get efficiency, the desired data, and deal with infinite strings by
using a function that is like 'inits' but which returns the initial strings
in reversed order.
reversed_inits = scanl (flip (:)) ""
find (isPrefixOf (reverse "needle")) (reversed_inits "haystack")
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