[racket] What do these symbols mean in Racket regexp documentation?

From: Danny Yoo (dyoo at hashcollision.org)
Date: Tue May 7 17:36:26 EDT 2013

On Tue, May 7, 2013 at 3:14 PM, Don Green <infodeveloperdon at gmail.com>wrote:

> Can you apply the verbage that must be represented by the symbols in
> Racket regexp documentation shown below:
> ;;= means what?
> | means what?
> <pces> means what?
Hi Don,

You are seeing instances of Backus-Naur Form (BNF):


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.

;;= means what?
> | means what?
> <pces> means what?
> When I read something like:




Match ‹*pces*›



Match either ‹*regexp*›, try left first

I read this as:

"A regular expression regexp is either:

    * A "pces", which will be defined later in the document,


    * An inner regexp, followed by a pipe "|", followed by another regexp



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.
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