Re: Alternative Syntax for Regular Expressions?

Hi Edward,


> In Hopcroft and Ullman's 1973 book FORMAL LANGUAGES AND THEIR
> RELATION TO AUTOMATA they were among the first to reveal the
> discovery that regular expressions corresponded to a particular type
> of language, "Chomsky Type 0" which they named in honor of MIT's
> Noam Chomsky who is both a pioneer in linguistics and a political
> gadfly.


Isn't Type 3 the regular grammar under Chomsky's classification?


> Backus-Naur grammars are more readable, by several orders of
> magnitude, than regular expressions.


Just change the regular expression syntax. Perl has done this. So's
Python. And lex gave names to parts of patterns.


> ^(\([0-9]{3}\)[ ]{1}){0,1}[0-9]{3}\-[0-9]{4}$ Yecchhhh


Just using some of these changes gives


        ^(\(\d\d\d\) )?\d\d\d-\d\d\d\d$


Why use a character class for the single space? Why suffix that class
with {1} which is redundant? Why use {0,1} instead of ?? Why escape
the dash?


You've made it more cluttered than necessary.


> phoneNumber := STARTOFINPUT phoneNumberBody ENDOFINPUT
> phoneNumberBody := localPhoneNumber
> phoneNumberBody := areaCode SPACE localPhoneNumber
> areaCode := [0-9]{3}
> localPhoneNumber := prefix DASH suffix
> prefix := [0-9]{3}
> suffix := [0-9]{4}


Some of those lines could be done exactly the same way in lex as I
mentioned earlier.


Cheers,


Ralph.

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