12 Commits (9446e07f6acba905481e2e71c0a37774e479be70)

Author SHA1 Message Date
David Majda e510ecc3d0 Switch from first/rest to head/tail in example grammars
In the past year I worked on various grammars where first/rest or
head/tail were used as labels for parts of lists. I found I associate
head/tail with a list immediately, while in case of first/rest I have to
"parse" grammar rules for a while before understanding their structure.

Moreover, I tend to assume that rest is a list of the same thigs as
first, but I don't have such assumption in case of head/tail. This
assumption was in conflict with the grammar structure.

I'm not sure how much these observations are applicable to others, but I
decided to act on them and switch from first/rest to head/tail.
9 years ago
David Majda cca41e6618 Quote |class| object literal key
It broke IE 8.
9 years ago
David Majda 2005345976 Complete rewrite of the CSS example grammar
This is a complete rewrite of the CSS example grammar. It is now based
on CSS 2.1 *including the errata* and the generated parser builds a
nicer syntax tree. There is also a number of cleanups, formatting
changes, naming changes, and bug fixes.

Beside this, the rewrite reflects how I write grammars today (as opposed
to few years ago) and what style I would recommend to others.
11 years ago
David Majda da9a32a5f3 Example grammars: Improve |parseInt| invocations
Instead of |parseInt("0x" + digits)| do |parseInt(digits, 16)|, which is
a bit cleaner.
11 years ago
David Majda 68c6452d8a CSS example grammar: Simplify |integer| and |float| rules
It's not necessary to parse |parts| in the |integer| and |float| rule
into integer/float value. Everywhere these rules are used the result is
converted back into string anyway.
11 years ago
David Majda 86769a6c5c Error handling: Make |?| return |null| on unsuccessful match
Before this commit, the |?| operator returned an empty string upon
unsuccessful match. This commit changes the returned value to |null|. It
also updates the PEG.js grammar and the example grammars, which used the
value returned by |?| quite often.

Returning |null| is possible because it no longer indicates a match
failure.

I expect that this change will simplify many real-world grammars, as an
empty string is almost never desirable as a return value (except some
lexer-level rules) and it is often translated into |null| or some other
value in action code.

Implements part of #198.
11 years ago
David Majda faaf9b6be1 Text nodes: Use text nodes in examples/css.pegjs 12 years ago
David Majda 5f810f803b Make example grammars compatible with Rhino 15 years ago
David Majda ee8c121676 Use labeled expressions and variables instead of $1, $2, etc.
Labeled expressions lead to more maintainable code and also will allow
certain optimizations (we can ignore results of expressions not passed
to the actions).

This does not speed up the benchmark suite execution statistically
significantly on V8.

Detailed results (benchmark suite totals):

---------------------------------
 Test #     Before       After
---------------------------------
      1   28.43 kB/s   28.46 kB/s
      2   28.38 kB/s   28.56 kB/s
      3   28.22 kB/s   28.58 kB/s
      4   28.76 kB/s   28.55 kB/s
      5   28.57 kB/s   28.48 kB/s
---------------------------------
Average   28.47 kB/s   28.53 kB/s
---------------------------------

Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.4 (KHTML, like Gecko) Chrome/5.0.375.55 Safari/533.4
15 years ago
David Majda 409ddf2ae8 Formatted all grammars more consistently and transparently
This is purely cosmetical change, no functionality was affected
(hopefully).
15 years ago
David Majda 698564a3c2 Replace ":" after a rule name with "="
I'll introduce labelled expressions shortly and I want to use ":" as a
label-expression separator. This change avoids conflict between the two
meanings of ":". (What would e.g. "foo: 'bar'" mean?  Rule "foo"
matching string "bar", or string "bar" labelled "foo"?)
15 years ago
David Majda 751a33715d Added example CSS parser. 15 years ago