Re: perl regular expression grammar

One comments: Your notation seems unnecessarily cumbersome. Why not
say


                <set> ::= "[" "^"? <set-item>+ "]"


as an abbreviation for:


><set> ::= "[" <set-items> "]" | "[^" <set-items> "]"
><set-items> ::= <set-item> | <set-item> <set-items>




?? It seems like not much is gained your way.


You have a few omissions:


In article 01-07-080, Alan Oursland <alan@oursland.net> wrote:
><quant> ::= <group>"*" | <group>"+" | <group>"?" | <group>"{"<bound>"}" | <group>


This should be:


<quant>::= <group>"*" | <group>"+" | <group>"?" | <group>"{"<bound>"}"
                  | <group>"*?" | <group>"+?" | <group>"??" | <group>"{"<bound>"}?"
                  | <group>


><group> ::= "("<re>")" | <term>


I think this should look more like this:


<group> ::= "("<qmod><re>")" | <term>
<qmod> ::= "" | "?:" | "?=" | "?>" | "?!" | "?<=" | "?<!"
                                    | <qexpr>
                                    | "?(" <num-or-expr> ")" <re-or-two>
                                    | "?"<modifs> | "?-"<modifs> | "?"<modifs>"-"<modifs>
<num-or-expr> ::= <num> | <qexpr>
<qexpr> ::= "?{" <expr> "}"
<re-or-two> ::= <concat> | <concat> "|" <concat>
<modifs> ::= <modif> | <modif><modifs>
<modif> ::= "s" | "m" | "i" | "x"




I'll leave it up to you to figure out how to represent <expr>. The
rule is that Perl looks for the matching close brace, and backslashed
close-braces don't count on the way.


><char> ::= <non-meta> | "\"<escaped>
><non-meta> ::= any non-meta char
><escaped> ::= <meta>|<control>|<special>|<assert>


This isn't right, because "\d" is legal. It means the same as 'd'.




><hexchar> ::= "x"<hex><hex> | "x{"<hex><hex><hex><hex>"}"


\x3 is also legal.


Hope this helps, although I'm not sure what you're trying to accomplish.


--
@P=split//,".URRUU\c8R";@d=split//,"\nrekcah xinU / lreP rehtona tsuJ";sub p{
@p{"r$p","u$p"}=(P,P);pipe"r$p","u$p";++$p;($q*=2)+=$f=!fork;map{$P=$P[$f^ord
($p{$_})&6];$p{$_}=/ ^$P/ix?$P:close$_}keys%p}p;p;p;p;p;map{$p{$_}=~/^[P.]/&&
close$_}%p;wait until$?;map{/^r/&&<$_>}%p;$_=$d[$q];sleep rand(2)if/\S/;print

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