refactor(tazjin/rlox): Move entrypoints into interpreters

Right now this introduces a simple mechanism to flip between the
interpreters.

Change-Id: I92ee920c53d76ab6b664ac671993a6d6426af61a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2412
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

users/tazjin/rlox/src/main.rs

@@ -4,56 +4,16 @@ use std::io;
 use std::io::Write;
 use std::process;
 
+mod bytecode;
 mod errors;
 mod parser;
 mod scanner;
 mod treewalk;
 
 fn main() {
-    let mut args = env::args();
-
-    if args.len() > 2 {
-        println!("Usage: rlox [script]");
-        process::exit(1);
-    } else if let Some(file) = args.nth(1) {
-        run_file(&file);
-    } else {
-        run_prompt();
-    }
-}
-
-// Run Lox code from a file and print results to stdout
-fn run_file(file: &str) {
-    let contents = fs::read_to_string(file).expect("failed to read the input file");
-    let mut lox = treewalk::interpreter::Interpreter::create();
-    run(&mut lox, &contents);
-}
-
-// Evaluate Lox code interactively in a shitty REPL.
-fn run_prompt() {
-    let mut line = String::new();
-    let mut lox = treewalk::interpreter::Interpreter::create();
-
-    loop {
-        print!("> ");
-        io::stdout().flush().unwrap();
-        io::stdin()
-            .read_line(&mut line)
-            .expect("failed to read user input");
-        run(&mut lox, &line);
-        line.clear();
-    }
-}
-
-fn run(lox: &mut treewalk::interpreter::Interpreter, code: &str) {
-    let chars: Vec<char> = code.chars().collect();
-
-    let result = scanner::scan(&chars)
-        .and_then(|tokens| parser::parse(tokens))
-        .and_then(|program| lox.interpret(program).map_err(|e| vec![e]));
-
-    if let Err(errors) = result {
-        report_errors(errors);
+    match env::var("LOX_INTERPRETER").as_ref().map(String::as_str) {
+        Ok("treewalk") => treewalk::main(),
+        _ => bytecode::main(),
     }
 }