On Tue, Apr 9, 2013 at 1:33 AM, Tassilo Horn <t...@gnu.org> wrote:
> Nice, but providing the grammar as a plain string looks somewhat
> unnatural to me. Why not something like this (parser being a macro)?
>
> (def as-and-bs
> (parser
> S = AB* .
> AB = A B .
> A = "a" + .
> B = "b" + .))
>
> I.e., symbols denote non-terminals, strings denote terminals, and the
> dot indicates the end of a rule.
>
> Bye,
> Tassilo
>
I played around with that, but even if you suppress evaluation by using a
macro, Clojure's reader makes strong assumptions about certain symbols.
For example, it is standard in EBNF notation for {} to mean zero-or-more.
But if you include {A B C} in your grammar using the macro approach,
Clojure's reader will throw an error because it treats {} as a map and
expects an even number of forms to follow. That was the main reason, but
it also makes the notation much more sensitive to whitespace (for example,
AB * versus AB*). Gradually, those little issues start making it look less
and less like traditional notation. There's something really nice about
just being able to copy and paste a grammar off of a website and have it
just work.
I understand where you're coming from, though. It definitely is part of
the Clojure culture to avoid string representations for many kinds of data
(e.g., SQL queries). We do accept it for regular expressions, and for
things like #inst "2011-12-31T19:00:00.000-05:00", though, and that's the
kind of feel I was going for. Would it be more psychologically palatable
to type:
#insta/parser "S = 'a' 'b'"
rather than
(insta/parser "S = 'a' 'b'")
?
What do you think would be gained by making it a macro? From my
perspective, a macro is essentially just a string that is being processed
by the Clojure reader (and thus subject to its constraints). If the
grammar were expressed in the way you propose, is it any easier to build up
a grammar programmatically? Is it any easier to compose grammars? If
anything, I think it might be harder.
Thanks for the comments,
Mark
--
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to clojure+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.
