<div dir="ltr"><br><div class="gmail_extra"><br><br><div class="gmail_quote">On Tue, May 7, 2013 at 3:14 PM, Don Green <span dir="ltr"><<a href="mailto:infodeveloperdon@gmail.com" target="_blank">infodeveloperdon@gmail.com</a>></span> wrote:<br> <blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"> <p style="margin-bottom:0in">Can you apply the verbage that must be represented by the symbols in Racket regexp documentation shown below:</p> <p style="margin-bottom:0in">;;= means what?</p> <p style="margin-bottom:0in">| means what?</p><p style="margin-bottom:0in"><pces> means what?</p><p style="margin-bottom:0in"></p></div></blockquote><div><br></div><div style>Hi Don,</div><div style><br></div><div style> <br></div><div style>You are seeing instances of Backus-Naur Form (BNF):</div><div style><br></div><div style> <a href="http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form">http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form</a><br> </div><div><br></div><div style>This is not exclusive to Racket documentation. It is a syntax that is commonly used in computer science to express the structure of a language.</div><div style><br></div><div style><br></div> <div style><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"><p style="margin-bottom:0in">;;= means what?</p> <p style="margin-bottom:0in">| means what?</p><p style="margin-bottom:0in"><pces> means what?</p><p style="margin-bottom:0in"></p></div></blockquote></div><div style>When I read something like:</div><div style><br> </div> <div style><br class=""><table cellpadding="2" cellspacing="0" width="474"><colgroup><col width="5"><col width="54"><col width="26"><col width="110"><col width="4"><col width="219"><col width="29"></colgroup><tbody><tr><td width="5" style="border:medium none;padding:0in"> <p align="LEFT"> </p></td><td width="54" style="border:medium none;padding:0in"><p align="LEFT">‹<i>regexp</i>›</p></td><td width="26" style="border:medium none;padding:0in"><p align="CENTER"> ::= </p></td><td width="110" style="border:medium none;padding:0in"> <p align="LEFT">‹<i>pces</i>›</p></td><td width="4" style="border:medium none;padding:0in"><p align="LEFT"> </p></td><td width="219" style="border:medium none;padding:0in"><p align="LEFT">Match ‹<i>pces</i>›</p></td><td width="29" style="border:medium none;padding:0in"> <br></td></tr><tr><td width="5" style="border:medium none;padding:0in"><p align="LEFT"> </p></td><td width="54" style="border:medium none;padding:0in"><p align="LEFT"> </p></td><td width="26" style="border:medium none;padding:0in"> <p align="CENTER">|</p></td><td width="110" style="border:medium none;padding:0in"><p align="LEFT">‹<i>regexp</i>›|‹<i>regexp</i>›</p></td><td width="4" style="border:medium none;padding:0in"><p align="LEFT"> </p></td><td width="219" style="border:medium none;padding:0in"> <p align="LEFT">Match either ‹<i>regexp</i>›, try left first</p></td><td width="29" style="border:medium none;padding:0in"><p align="LEFT"><br></p></td></tr><tr></tr></tbody></table></div><div style><br></div><div style> I read this as:<br> </div><div style><br></div><div style><br></div><div style>"A regular expression regexp is either:</div><div style><br></div><div style> * A "pces", which will be defined later in the document, </div><div style> <br></div><div style>OR</div><div style><br></div><div style> * An inner regexp, followed by a pipe "|", followed by another regexp</div><div style><br></div><div style>OR</div><div style><br></div><div style> ...</div><div style><br></div><div style><br></div><div style>where ":==" is notation meant to distinguish the left and right hand sides of the definition, <X> is a reference to another piece of structure, and "|" is mean to denote one of a possible set of candidates.</div> <div style><br></div></div></div></div>