In May there was some discussion on the possibility of a standardized
format for the ECMAScript AST in JSON/JsonML.
The V8 engine has an option (in bleeding_edge) where the internal AST
tree can be output to JsonML for debugging purposes:
./shell_g --print_json_ast <file.js>
This is V8's internal AST type, which necessarily includes some
implementation-specific artifacts. That said, the V8 AST is very
nearly straight out of the ECMA 262 spec, so it's pretty generic.
(Note: it's an initial version e.g doesn't recur into switch statement
cases). It could be useful as an input as to what a standard JSON AST
should look like. (Which, i guess, ECMAScript engines could support as
an new, additional format to any existing AST serialization formats).
Here's an example - with some V8 artefact's removed for clarity. Note:
the script gets wrapped in a FunctionLiteral and VariableProxy ==
Identifier.
--- source ---
x = 1;
if (x > 0) {
y = x + 2;
print(y);
}
--- AST JsonML ---
["FunctionLiteral",
{"name":""},
["ExpressionStatement",
["Assignment",
{"op":"ASSIGN"},
["VariableProxy",
{"name":"x"}
],
["Literal",
{"handle":1}
]
]
],
["IfStatement",
["CompareOperation",
{"op":"GT"},
["VariableProxy",
{"name":"x"}
],
["Literal",
{"handle":0}
]
],
["Block",
["ExpressionStatement",
["Assignment",
{"op":"ASSIGN"},
["VariableProxy",
{"name":"y"}
],
["BinaryOperation",
{"op":"ADD"},
["VariableProxy",
{"name":"x"}
],
["Literal",
{"handle":2}
]
]
]
],
["ExpressionStatement",
["Call",
["VariableProxy",
{"name":"print"}
],
["VariableProxy",
{"name":"y"}
]
]
]
],
["EmptyStatement"]
]
]
3
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