Re: A minimal LL(1) parser generator ?

carlglassberg@gmail.com writes:
>Gray's meta notation uses a postix operator "&&" for "separator list".
>
>"&&" seems particularly elegant and interesting:
>
>If Gray: "a b &&" ---> EBNF: "a { b a }"
>
>then I assume:
>
>"a b && c &&" ---> "a { b a } { c a }"


The left operand of the second && would be "a b &&", so the whole
thing would be equivalent to


a {b a} {c {a {b a}}}


a (( b || c )) &&


would parse the same strings, but with different parse trees; so if
you add actions, the results would probably be different.


>and so on ...
>
>Further "a b && b && ..." ===> "a b &&"


They describe the same strings, yes. However, the former has an
ambiguous grammar that allows to parse "aba" in two ways: either the b
is the first b or the second one. In Gray, this leads to a conflict
(it just can deal with LL(1) grammars), and I guess one of these
parsing options never be exercised, which means that it works as if
you had written "a b &&" in the first place.


- anton
--
M. Anton Ertl
anton@mips.complang.tuwien.ac.at
http://www.complang.tuwien.ac.at/anton/

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