From: Eric Schwartz <emschwar@...>
Date: 2005-04-27T06:44:30+09:00
Subject: Re: Is Ruby grammar context free?

Peter Suk <peter.kwangjun.suk@mac.com> writes:
> Okay, this part is probably context free.  I can come up with a context 
> free grammar for something analogous:
>
> 	X -> S1 d | S2
> 	S1 -> a S1 b | c
> 	S2 -> a S2 b | <empty>
>
> This produces the language { a^n c b^n d } where x ^ n denotes x 
> repeated n times.

Actually, the c and d are optional:

X -> S2
X -> a S2 b
X -> a b

and by implication

X -> a^n b^n

I'm not sure how that affects your attempt to replicate heredocs in a
CFG.

-=Eric
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