[antlr-interest] Use each token Once -- All required
Terence Parr
parrt at cs.usfca.edu
Tue Sep 21 11:05:32 PDT 2004
Hi. Restriction on number can be encoded in syntax but as you point
out combinations are combinatorial in size ;)
I suggest simply using the first XXX rule and then an action at the end
that asks if everything is covered exactly once. Perhaps a bitset
updated in each alt and then simply checked at the end.
The distinction between syntax and semantics is very often blurred. :)
Terence
On Sep 21, 2004, at 8:15 AM, georgehernando wrote:
>
> How can I specify a compact syntax for the parser that will define a
> list of token types from the lexer where each type must appear, but
> only one time?
>
> XXX : (TokenType1 | TokenType2 | TokenType3 | TokenType4)+;
> doesn't limit the token types to appearing only one time.
>
> Do I have to specify all permutations?
>
> XXX : ( (TokenType1 TokenType2 TokenType3 TokenType4) |
> (TokenType1 TokenType2 TokenType4 TokenType3) |
> (TokenType1 TokenType4 TokenType3 TokenType2) |
> (TokenType4 TokenType2 TokenType3 TokenType1) |
> (TokenType2 TokenType1 TokenType3 TokenType4) |
> ....
> )
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
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