// A partial Scheme implementation in Rust
// Build with: rustc minimal.rs -o minimal-rust

use std::io;
use std::io::Write;

// There doesn't seem to be a symbole or quote type in Rust, so i'm going to use strings and
// vectors

// "list of tokens" implemented as a vector of String.
// AST implemented as nested tuples (immutable).

//let const SCHEME_BUILTINS = ("lambda", "quote", "cond", "else", "cons", "car", "cdr", "null?", "eq?", "atom?", "zero?", "number?", "+", "-", "*", "/");

#[allow(dead_code)]
enum SchemeAtom<'a> {
    SchemeNull,
    SchemeTrue,
    SchemeFalse,
    SchemeNum(f64),
    SchemeBuiltin(&'a str),
    SchemeStr(&'a str),
}

enum SchemeExpr<'a> {
    SchemeAtom(SchemeAtom<'a>),
    SchemeList(Vec<SchemeExpr<'a>>),
}

///////////////////////////////////

fn is_zero(n: f64) -> bool {
    return n == 0.;
}

///////////////////////////////////

fn scheme_tokenize(s: &String) -> Result<Vec<&String>, &'static str> {
    let ret = vec![s];
    return Ok(ret);
}

fn scheme_parse_num(s: &String) -> Result<f64, &'static str> {
    let num = 0.;
    return Ok(num);
}

fn scheme_parse_sexpr(sexpr: Vec<&String>) -> Result<SchemeExpr, &'static str> {
    let ret = sexpr.into_iter().map(|el| SchemeExpr::SchemeAtom(SchemeAtom::SchemeStr(el))).collect();
    return Ok(SchemeExpr::SchemeList(ret))
}

fn scheme_parse(tokens: SchemeExpr) -> Result<SchemeExpr, &'static str> {
    return Ok(SchemeExpr::SchemeAtom(SchemeAtom::SchemeNull));
}

fn scheme_eval(ast: SchemeExpr) -> Result<SchemeExpr, &'static str> {
    return Ok(SchemeExpr::SchemeAtom(SchemeAtom::SchemeNull));
}

fn scheme_repr(ast: SchemeExpr) -> Result<String, &'static str> {
    return Ok("It Worked!".to_string());
}

fn main() {

    let stdin = io::stdin();
    let mut stdout = io::stdout();
    let raw_input = &mut String::new();

    loop {
        stdout.write(b"\nminimal-rust> ").unwrap();
        stdout.flush().unwrap();
        raw_input.clear();
        stdin.read_line(raw_input).unwrap();
        if raw_input.len() == 0 {
            stdout.write(b"\nCiao!\n").unwrap();
            return;
        }
        let tokens = scheme_tokenize(raw_input).unwrap();
        let sexpr = scheme_parse_sexpr(tokens).unwrap();
        let ast = scheme_parse(sexpr).unwrap();
        let resp = scheme_eval(ast).unwrap();
        println!("{}", scheme_repr(resp).unwrap());
    }
}