On Fri, Oct 10, 2014 at 4:18 PM, Jon Fairbairn wrote:

That seems rather wordy to me. Can we get anywhere starting with

a `isSuffixOf` b = a `elem` tails b

and transforming?

Is it only about wordiness & syntax? With the original a `isSuffixOf` b = reverse a `isPrefixOf` reverse b and with Jon's a `isSuffixOf` b = a `elem` tails b I'm completely convinced of the correctness, modulo that of the referenced functions. Moreover, the conviction was obtained cheaply. My finite neurons are saved for the greater task at hand. The proposal on the table snatches away that providence. I have to take it on the authority of others that it's correct. Rust recently exposed a bug in their string matching function. It's their version of Data.List.isInfixOf. See http://www.wabbo.org/blog/2014/22aug_on_bananas.html These days I point all my colleagues and friends to this article as a classic case of premature optimization. But I understand that some folks prefer their computations always rapid, if sometimes wrong. David, is there an application underlying the need for isSuffixOf speed? You might want to look into the ByteString libraries for your optimization efforts. Over there, performance is several notches up in priority. -- Kim-Ee