Fix the following errors:
59:35 error "options" is defined but never used no-unused-vars
91:11 error "plugin" is defined but never used no-unused-vars
102:35 error "options" is defined but never used no-unused-vars
128:35 error "options" is defined but never used no-unused-vars
Note that ESLint revealed a real problem where the test supposedly
verifying receiving options by a plugin didn't actually verify anything.
Implement the swap and change various directives in the source code. The
"make hint" target becomes "make lint".
The change leads to quite some errors being reported by ESLint. These
will be fixed in subsequent commits.
Note the configuration enables just the recommended rules. Later I plan
to enable more rules to enforce the coding standard. The configuration
also sets the environment to "node", which is far from ideal as the
codebase contains a mix of CommonJS, Node.js and browser code. I hope to
clean this up at some point.
Parsers can now be generated with support for tracing using the --trace
CLI option or a boolean |trace| option to |PEG.buildParser|. This makes
them trace their progress, which can be useful for debugging. Parsers
generated with tracing support are called "tracing parsers".
When a tracing parser executes, by default it traces the rules it enters
and exits by writing messages to the console. For example, a parser
built from this grammar:
start = a / b
a = "a"
b = "b"
will write this to the console when parsing input "b":
1:1 rule.enter start
1:1 rule.enter a
1:1 rule.fail a
1:1 rule.enter b
1:2 rule.match b
1:2 rule.match start
You can customize tracing by passing a custom *tracer* to parser's
|parse| method using the |tracer| option:
parser.parse(input, { trace: tracer });
This will replace the built-in default tracer (which writes to the
console) by the tracer you supplied.
The tracer must be an object with a |trace| method. This method is
called each time a tracing event happens. It takes one argument which is
an object describing the tracing event.
Currently, three events are supported:
* rule.enter -- triggered when a rule is entered
* rule.match -- triggered when a rule matches successfully
* rule.fail -- triggered when a rule fails to match
These events are triggered in nested pairs -- for each rule.enter event
there is a matching rule.match or rule.fail event.
The event object passed as an argument to |trace| contains these
properties:
* type -- event type
* rule -- name of the rule the event is related to
* offset -- parse position at the time of the event
* line -- line at the time of the event
* column -- column at the time of the event
* result -- rule's match result (only for rule.match event)
The whole tracing API is somewhat experimental (which is why it isn't
documented properly yet) and I expect it will evolve over time as
experience is gained.
The default tracer is also somewhat bare-bones. I hope that PEG.js user
community will develop more sophisticated tracers over time and I'll be
able to integrate their best ideas into the default tracer.
David Majda
Arlo Breault