JavaScript allows one to skip (elide) elements in array literals. It
also allows a trailing comma, which doesn't imply an element elision.
For example, an array literal:
[,,,]
contains three elided elements (one before each comma) and a trailing
comma.
Example JavaScript parser handled elided elements incorrectly and just
threw them away. This commit fixes this behvior and inserts |null| in
the AST for each elided element. This is in line with how SpiderMonkey's
JavaScript parser (the |Reflect.parse| API), Esprima and Acorn behave.
Based on a patch by @fpirsch:
https://github.com/dmajda/pegjs/pull/177
Makes the |ArrayLiteral| and |ElementList| rules more in line with the
ECMAScript grammar.
Based on a patch by @fpirsch:
https://github.com/dmajda/pegjs/pull/177
We couldn't return |null| in the |value| rule of the JSON example
parser because that would mean parse failure. So until now, we just
returned |"null"| (a string).
This was obviously stupid, so this commit changes the |value| rule to
return a special object instead that is converted to |null| later.
Based on patches by Patrick Logan (GH-91) and Jakub Vrána (GH-191).
Fix automatic semi-colon insertion in var statements without
initialisers.
var i
i = 1;
is valid and not accepted by the parser
but
var i = 2
i = 3;
is valid and accepted by the parser, as it should be.
With this fix, both are accepted.
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"?)
David Majda
fpirsch
Jason Davies