<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On 26 May 2011, at 16:26, Alexander Kuleshov wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Hello,<br><br>How can i fast replace 2 elements in Erlang list? For example I have<br>list: [1,2,3,4], how can i quickly get [1,3,2,4]?<font class="Apple-style-span" color="#000000"><font class="Apple-style-span" color="#144FAE"><br></font></font></div></blockquote><br></div><div>From your example, I read the question as "How can I *swap* 2 elements in an Erlang list?"</div><div><br></div><div>swap([X, Y | T], X, Y) -></div><div> [Y, X | T];</div><div>swap([H | T], X, Y) -></div><div> [H | swap(T, X, Y)].</div><div><br></div><div>Decisions to be made include:</div><div><br></div><div>- swap every instance or just the first pair?</div><div>- what to do at the end of the list (do we require that there should be at least one matching pair?)</div><div><br></div><div>I think this is a fairly good example of the kind of operation that, while seemingly generic, is not a particularly good candidate for a library function; it's so easy to implement with the exact semantics you require for your problem, and there *are* possible variants.</div><div><br></div><div>BR,</div><div>Ulf W</div><br><div>
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div>Ulf Wiger, CTO, Erlang Solutions, Ltd.</div><div><a href="http://erlang-solutions.com">http://erlang-solutions.com</a></div><div><br></div></span><br class="Apple-interchange-newline">
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