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

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):

    http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form

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:




‹*regexp*›

 ::=

‹*pces*›



Match ‹*pces*›





|

‹*regexp*›|‹*regexp*›



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,

OR

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

OR

    ...


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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