Ouroboros

A metacircular evaluator for a subset of javascript connected to a runtime extensible top down operator precedence parser.

Purpose

To bootstrap a full ecmascript3 interpreter from the smallest possible base language.

Restricted Javascript

The subset used to bootstrap the parser and interpreter is as minimal as possible and aimed at being easy to compile statically or optimise in a just in time compiler.

• No Prototypes
• Arrays have a static length
• Arrays abort for out of bounds access
• Objects have static keys (set at creation time)
• Objects abort on invalid key access
• No Coercion, operators that use it are missing or fail with incorrect left/right types
• No for loops, only while loops
• Limited set of arithmetic operators (no ++, -- prefix or postfix)
• No closures, global scope and local variables only
• Only let is available for variable creation
• No dangling commas
• Semicolons are mandatory
• No new keyword or classes
• no this keyword or automated object method scoping
• no dynamic method lookup (obj["func"](arg), including array indexing)
• Errors trigger abort on construction
• No try/catch blocks

Some of these might be relaxed in the future in cases where the parser can figure out that the expression is actually static despite using dynamic syntax.

TODO

• Write lexer in restricted js
• Write parser in restricted js
• Write interpreter in restricted js
• Execute lexer in meta-vm
• Execute parser in meta-vm
• Execute meta-vm inside the meta-vm :)
• Walk the heap and compile the meta-vm into C
• Use the cross-compiled meta-vm to run the meta-vm inside the meta-vm :D
• Add evaluation of top-level statements to the parser using the meta-vm
• Climb the turing tarpit up to es3
• Climb further to es6
• Implement node specialization in evaluator
• Implement bytecode compilation in evaluator
• Finally, Implement a meta-tracing just-in-time compiler