This improves the lexing of escape sequences within strings that appear in a grammar. It relies on Racket’s `read` to interpret these escape sequences rather than a hard-coded hash table. This gives strings in a grammar pretty much the same semantics as standard Racket strings, including support for octal and hex escape sequences for Unicode codepoints.
Though this passes all current tests, there are still some oddball corner cases that can be discovered by sticking together certain combinations of escape sequences (backslashes, double quotes, and codepoints). The better solution would be to peek into the input port for a double quote, and if it’s there, use the standard Racket lexer to pull out the string (this lexer already handles the weirdo cases). We can’t do this, however, because brag also supports single-quoted strings, which need to have the same semantics, and the Racket lexer won’t work with those. So I think we’re stuck with the homegrown solution (for consistency with both kinds of quotes) even at the expense of a few unresolved corner cases. Let’s leave that question for another day, as these cases haven’t surfaced in practical use thus far.
I copied in the actual file contents. It would perhaps be safest to do
some sort of "read the file and splice the contents in," but I'm not
sure how to do that at the moment.
When using `make-rule-parser` for any rule that is not the start
rule, and applying the resulting parser while giving it a source-path
it would just use the entire grammar from the start rule.
The natural-number? predicate seems to be
unavailable (though there is a remnant of it in the form of
natural-number/c, which is just a contract alias of
exact-nonnegative-integer?). In any case, it surely means
nonnegative integer.
(One might push the envelope here slightly and add
exactness, but this commit does not go that far.)
The broken link showed up as an undefined tag warning for `(tech "comment")` when installing this package.
This seemed like the most straightforward fix, but it's a bit wordy.
Matthew Butterick