scala 0.1.1

A experimental Scala interpreter written in Rust: lexer, parser, type inference, and tree-walking evaluation with a REPL.
Documentation 
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pub mod token;
pub mod lexer;
pub mod ast;
pub mod parser;
pub mod ty;
pub mod typechecker;
pub mod value;
pub mod env;
pub mod interpreter;
pub mod stdlib;
pub mod repl;

pub fn run_file(source: &str, check_only: bool, dump_tokens: bool, dump_ast: bool) -> Result<(), String> {
    let tokens = lexer::Lexer::tokenize(source)
        .map_err(|e| format!("lexer error: {}", e))?;

    if dump_tokens {
        for token in &tokens {
            println!("{:?}", token);
        }
        return Ok(());
    }

    let stmts = parser::Parser::parse(tokens)
        .map_err(|e| format!("parse error: {}", e))?;

    if dump_ast {
        for stmt in &stmts {
            println!("{}", ast::fmt_stmt(stmt, 0));
        }
        return Ok(());
    }

    if check_only {
        typechecker::typecheck_program(&stmts)
            .map_err(|errs| {
                errs.iter().map(|e| e.to_string()).collect::<Vec<_>>().join("\n")
            })?;
        println!("Type check passed.");
        return Ok(());
    }

    let mut interp = interpreter::Interpreter::new();
    let _ = interp.run_source(source)
        .map_err(|e| format!("{}", e))?;

    Ok(())
}

/// Parse and type-check, then interpret. Fails if lex, parse, typecheck, or runtime errors.
pub fn typecheck_then_run(source: &str) -> Result<value::Value, String> {
    typechecker::typecheck_source(source).map_err(|errs| {
        errs.iter()
            .map(std::string::ToString::to_string)
            .collect::<Vec<_>>()
            .join("\n")
    })?;
    interpreter::Interpreter::new()
        .run_source(source)
        .map_err(|e| e.to_string())
}

/// Interpret only (no static type pass), same as [`interpreter::Interpreter::run_source`] on a fresh interpreter.
pub fn interpret_source(source: &str) -> Result<value::Value, interpreter::RuntimeError> {
    interpreter::Interpreter::new().run_source(source)
}