Before this change, the start rule was the one named "start" and there
was an option to override that. This is now impossible.
The goal of this change is to contain all information for the parser
generation in the grammar itself.
In the future, some override directive for the start rule (like Bison's
"%start") may be added to the grammar.
Little change in the source grammar now does not change variables in all
the generated code. This is helpful especially when one has the
generated grammar stored in a VCS (this is true e.g. for our
metagrammar).
We want to have the rule parsing functions inside the |parse| method
because we want them to share a common environment. In the future,
initializers will be executed in this enviromnent and thus functions and
variables defined by them will be accessible to the rule parsing
functions.
Moving various private properties from the parser object into the
|parse| method was not strictly necessary, but it was a natural step
after moving the functions.
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
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"?)
This shouldn't have measurable effect on the benchmarks as there are no
proxy rules in the grammars the benchamrk uses. However the effect on
generated parsers' speed should be positive generally.
In most cases, code pattern
x === undefined
was transformed to
typeof(x) === "undefined"
and similarly with |!==|.
In the generated code, the condition was simply made less strict to
avoid performance penalty of string comparison (I don't think JavaScript
VMs optimize this specific pattern to avoid it).
The action now computes the number of passed parameters during the code
generation and the parameters are declared directly as $1, $2, etc. in the
generated function.
This does not speed up the benchmark suite execution statistically significantly
on V8.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 28.68 kB/s 29.08 kB/s
2 28.77 kB/s 28.72 kB/s
3 28.89 kB/s 28.78 kB/s
4 28.84 kB/s 28.57 kB/s
5 28.86 kB/s 28.84 kB/s
---------------------------------
Average 28.81 kB/s 28.80 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.2 (KHTML, like Gecko) Chrome/5.0.342.9 Safari/533.2
This does not speed up the benchmark suite execution statistically significantly
on V8.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 28.84 kB/s 28.75 kB/s
2 28.76 kB/s 28.69 kB/s
3 28.72 kB/s 28.69 kB/s
4 28.84 kB/s 28.93 kB/s
5 28.82 kB/s 28.70 kB/s
---------------------------------
Average 28.80 kB/s 28.75 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.2 (KHTML, like Gecko)
Chrome/5.0.342.9 Safari/533.2
This does not speed up the benchmark suite execution statistically significantly
on V8.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 28.72 kB/s 28.84 kB/s
2 28.84 kB/s 28.76 kB/s
3 28.83 kB/s 28.72 kB/s
4 28.81 kB/s 28.84 kB/s
5 28.76 kB/s 28.82 kB/s
---------------------------------
Average 28.79 kB/s 28.80 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.2 (KHTML, like Gecko) Chrome/5.0.342.9 Safari/533.2
This and also speeds up the benchmark suite execution by 7.83 % on V8.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 26.17 kB/s 28.16 kB/s
2 26.05 kB/s 28.16 kB/s
3 25.99 kB/s 28.10 kB/s
4 26.13 kB/s 28.11 kB/s
5 26.14 kB/s 28.07 kB/s
---------------------------------
Average 26.10 kB/s 28.14 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.2 (KHTML, like Gecko) Chrome/5.0.342.7 Safari/533.2
The Rhino bug that prevented inclusion of \uFEFF among the whitespace characters
is no longer relevant here because we compile character classes into regexps
now, which avoids the infinite recursion.
David Majda