Comments on: Text parsing, formal grammars and BNF introduction

By: Abhay Joshi

Abhay Joshi — Mon, 14 Mar 2011 18:03:53 +0000

I think tht the line
“An integer is a non-zero digit, or a non-zero digits followed by an arbitrary amount of digits.”
should be modified as
“An integer is a digit, or a non-zero digit followed by an arbitrary amount of digits.”
because your BNF looks like
nzdigit ::= 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
digit ::= 0 | nzdigit
digits ::= digit | digit digits
integer ::= digit | nzdigit digits
and hence 0 is a valid integer.

By: Divya

Divya — Wed, 15 Sep 2010 13:11:41 +0000

Hi,
I’m going to use BNF for the first time. Just going through online informations.
Could you please tell me good docs if any.
Thanks!

By: preeti

preeti — Sat, 30 Jan 2010 17:16:02 +0000

hi i need a source coding,to check the given expression in numbers is valid or not by using c programming

By: sar

sar — Fri, 23 May 2008 17:52:30 +0000

Hi,

I’am a student , and as a project I have to write a grammar (LBNF one) -and it’s ok for it-; then, I have to use the BNFC, and that’s th e pb i.e. Idon’t know how to use it.

Please help me. and thanks a lot.

Best regards.

By: ethana2

ethana2 — Mon, 21 Jan 2008 08:45:27 +0000

Lojban would have been perfect if it had a proper phonetic base.
After I fork it and make the Best Language on Earth, we can avoid this nonsense

By: RubenV

RubenV — Sun, 20 Jan 2008 19:52:46 +0000

Nicolas: You’re cheating there by combining recursion and regular expressions . Pure regular expressions can’t do that. Recursion is actually what sets regular languages and context free grammars apart.

By: Nicolas

Nicolas — Sun, 20 Jan 2008 18:30:02 +0000

no one in particular: indeed... I translated it somewhat badly. So to be correct:

whole_number ::= digit | nzdigit digits
sign ::= "-" | "+" | ""
integer ::= sign whole_number

Ruben: out of my head, if input is 'foo(bar(baz)bat)', can't you do something like

parts = []
regex = '^([.^(]*)[\(([.^)]*)\)]*(.*)$'

def parse(s):
    parts = regex.parse(s)
    parts.append(parts[0])
    for i in range(1, len(parts)):
        parse(parts[i])

parse(s)

By: RubenV

RubenV — Sun, 20 Jan 2008 17:46:42 +0000

Nicolas: Try expressing a language which recognizes balanced brackets, which can be arbitrarily nested using a regular expression.

Fairly trivial in BNF, impossible to implement using traditional regular expressions.

By: no one in particular

no one in particular — Sun, 20 Jan 2008 17:46:14 +0000

For the record, note that you’ve described the whole numbers, not the integers, because integers include negative numbers.

(I’m not trying to be annoying, but I figured it was worth pointing out. Thanks for the interesting read!)

By: Mattias Bengtsson

Mattias Bengtsson — Sun, 20 Jan 2008 14:32:19 +0000

I’ve been using BNFC (BNF Converter) for some compiler construction courses at school. I think it is a really neat project. It can generate Java, Haskell and C++-parsers. I’m not sure if it can output Python parsers though.