Subj : Re: help with ebnf for ebnf newbie?
To   : comp.programming
From : rossum
Date : Thu Sep 15 2005 12:08 am

On 11 Sep 2005 12:31:30 -0700, "pantagruel" <bry@itnisk.com> wrote:

>I don't have any experience with EBNF or just normal BNF, and I want to
>define a comma seperated string of name value pairs, with some
>predefined names, although no names that are required, the associator
>between name and value should be a '=' character. I am thinking
>something like this:
>
><value-list> ::= DefaultNames | Name "=" Value ","| <value-list>
Can <value-list> be empty?  Your definition does not allow it to be.
Your third option is <value-list> ::= <value-list> which is not very
useful.

>DefaultNames  ::=  "callid=" Value "," | "callfrom=" Value
"callid=" is followed by a comma and "callfrom=" is not.  Also you
have an or in the middle, judging by your example you should probably
concatenate instead since you seem to want both callid and callfrom on
the same line.

Would "callid =" (with a space) be accepted?

>Value ::= <Text, excluding CR/LF>
Can a Value be "callfrom" or "callid"? Can a Value include spaces?
>Name ::= <Text, excluding CR/LF>
Can a Name include spaces?

>
>
>this should match
>
>callid=wotcha,callfrom=whoyathunk,testing=othervalue
                comma not matched ^
>
>
>is this wrong?
Yes I'm afraid.


You might want to introduce the definition of a Name-Value pair.  This
saves a lot of commas elsewhere in the definitions.  Since you want to
describe a comma separated list then just start by defining a comma
separated list:

<value-list> ::= <name-value-pair> |
                 <name-value-pair> "," <value_list>

You can use the <name-value-pair> definition to describe what it is
that you are making a list of.

<name-value-pair> ::= ...


HTH

rossum



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