While debugging test failures, it's pretty frustrating to have to go do
printf debugging to figure out what test is failing right now. While
watching your JS Raytracer stream it seemed like this was pretty
furstrating as well. So I wanted to start working on improving the
diagnostics here.
In the future I hope we can eventually be able to plumb the info down
to the Error classes so any thrown exceptions will contain enough
metadata to know where they came from.
There is no such thing as a "undefined literal" in JS - undefined is
just a property on the global object with a value of undefined.
This is pretty similar to NaN.
var undefined = "foo"; is a perfectly fine AssignmentExpression :^)
You can now throw an expression to the nearest catcher! :^)
To support throwing arbitrary values, I added an Exception class that
sits as a wrapper around whatever is thrown. In the future it will be
a logical place to store a call stack.
This adds a basic Javascript lexer and parser. It can parse the
currently existing demo programs. More work needs to be done to
turn it into a complete parser than can parse arbitrary JS Code.
The lexer outputs tokens with preceeding whitespace and comments
in the trivia member. This should allow us to generate the exact
source code by concatenating the generated tokens.
The parser is written in a way that it always returns a complete
syntax tree. Error conditions are represented as nodes in the
tree. This simplifies the code and allows it to be used as an
early stage parser, e.g for parsing JS documents in an IDE while
editing the source code.:
