crafting-interpreter

My implementation of the lox programming language in rust following Crafting Intepretors (Try it out online at https://yangchenye323.github.io/lox/)

• Scanning
• Parsing ASTs The grammar of my lox implementation has several differences with the book, some of which are extensions:

• Automatic semicolon insertion: semicolons are automatically inserted at the end of statements if (i) the next token is on another line or (ii) the next token is EOF
• If and loop conditions don't need to be in parenthesis and braces are not omittable (similar to rust's if/loop syntax rather than C's)
• Break statement is suported.
• C-like ternary expression is implemented.
• Function formal parameters support default initialization: fun foo(a = 1, b = "A") {}, if no explicit default initialization is set, parameter is initialized to nil in cases no actual arguments is provided.
• Function can handle variable numbers of parameters, arity is not checked by the interpretor itself.
• Print statement is replaced with a builtin print function which handles arbitrary number of arguments.
• Shadow declaration is not an error:

var a = 1;
var a = 2; // OK

var a = 1;
var a = a + 1; // OK: a = 2

• "this" is a valid identifier rather than a reserved keyword, code like var this = 1 will compile. This identifier is only treated specially in that it will get bind to the object where a method is called. The binding rule is the same with the book, but users can overwrite the variable in the inner scope.

Tree Walk Interpretor:

• Evaluating expressions
• Evaluating statements and program state
• Control flow and loops
• Functions
• Closures
• Block level scoping rules

• Block scope is implementd at runtime rather than compile time, using the aproach of persistent runtime scope chain (See scope.rs)

• Class

• static member funtion is supported with the syntax:

class Foo {
  class staticMethod() {
  }
}

• inheritance and dynamic dispatch

• The "this" identifier is binded at method invocation time to the actual object on which the method is invoked.
• The "super" identifier is binded at method creation time to the super class, if any, of the method's defining class.

• An REPL terminal client with history support: cargo run -p rlox

Bytecode Virtual Machine

WIP