You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: step6_file.rs
    path of file: ./repos/mal/impls/rust
    
    the code of the file until where you have to start completion: use std::rc::Rc;
//use std::collections::HashMap;
use fnv::FnvHashMap;
use itertools::Itertools;

#[macro_use]
extern crate lazy_static;
extern crate fnv;
extern crate itertools;
extern crate regex;

extern crate rustyline;
use rustyline::error::ReadlineError;
use rustyline::Editor;

#[macro_use]
mod types;
use crate::types::MalVal::{Bool, Func, Hash, List, MalFunc, Nil, Str, Sym, Vector};
use crate::types::{error, format_error, MalArgs, MalErr, MalRet, MalVal};
mod env;
mod printer;
mod reader;
use crate::env::{env_bind, env_get, env_new, env_set, env_sets, Env};
#[macro_use]
mod core;

// read
fn read(str: &str) -> MalRet {
    reader::read_str(str.to_string())
}

// eval
fn eval_ast(ast: &MalVal, env: &Env) -> MalRet {
    match ast {
        Sym(_) => Ok(env_get(&env, &ast)?),
        List(v, _) => {
            let mut lst: MalArgs = vec![];
            for a in v.iter() {
                lst.push(eval(a.clone(), env.clone())?)
            }
            Ok(list!(lst))
        }
        Vector(v, _) => {
            let mut lst: MalArgs = vec![];
            for a in v.iter() {
                lst.push(eval(a.clone(), env.clone())?)
            }
            Ok(vector!(lst))
        }
        Hash(hm, _) => {
            let mut new_hm: FnvHashMap<String, MalVal> = FnvHashMap::default();
            for (k, v) in hm.iter() {
                new_hm.insert(k.to_string(), eval(v.clone(), env.clone())?);
            }
            Ok(Hash(Rc::new(new_hm), Rc::new(Nil)))
        }
        _ => Ok(
    
fn eval(mut ast: MalVal, mut env: Env) -> MalRet {
    let ret: MalRet;

    'tco: loop {
        ret = match ast.clone() {
            List(l, _) => {
                if l.len() == 0 {
                    return Ok(ast);
                }
                let a0 = &l[0];
                match a0 {
                    Sym(ref a0sym) if a0sym == "def!" => {
                        env_set(&env, l[1].clone(), eval(l[2].clone(), env.clone())?)
                    }
                    Sym(ref a0sym) if a0sym == "let*" => {
                        env = env_new(Some(env.clone()));
                        let (a1, a2) = (l[1].clone(), l[2].clone());
                        match a1 {
                            List(ref binds, _) | Vector(ref binds, _) => {
                                for (b, e) in binds.iter().tuples() {
                                    match b {
                                        Sym(_) => {
                                            let _ = env_set(
                                                &env,
                                                b.clone(),
                                                eval(e.clone(), env.clone())?,
                                            );
                                        }
                                        _ => {
                                            return error("let* with non-Sym binding");
                                        }
                                    }
                                }
                            }
                            _ => {
                                return error("let* with non-List bindings");
                            }
                        };
                        ast = a2;
                        continue 'tco;
                    }
                    Sym(ref a0sym) if a0sym == "do" => {
                        match eval_ast(&list!(l[1..l.len() - 1].to_vec()), &env)? {
                            List(_, _) => {
                                ast = l.last().unwrap_or(&Nil).clone();
                                continue 'tco;
                            }
                            _ => error("invalid do form"),
                        }
                    }
                    Sym(ref a0sym) if a0sym == "if" => {
                        let cond = eval(l[1].clone(), env.clone())?;
                        match cond {
                            Bool(false) | Nil if l.len() >= 4 => {
                                ast = l[3].clone();
                                continue 'tco;
                            }
                            Bool(false) | Nil => Ok(Nil),
                            _ if l.len() >= 3 => {
                                ast = l[2].clone();
                                continue 'tco;
                            }
                            _ => Ok(Nil),
                        }
                    }
                    Sym(ref a0sym) if a0sym == "fn*" => {
                        let (a1, a2) = (l[1].clone(), l[2].clone());
                        Ok(MalFunc {
                            eval: eval,
                            ast: Rc::new(a2),
                            env: env,
                            params: Rc::new(a1),
                            is_macro: false,
                            meta: Rc::new(Nil),
                        })
                    }
                    Sym(ref a0sym) if a0sym == "eval" => {
                        ast = eval(l[1].clone(), env.clone())?;
                        while let Some(ref e) = env.clone().outer {
                            env = e.clone();
                        }
                        continue 'tco;
                    }
                    _ => match eval_ast(&ast, &env)? {
                        List(ref el, _) => {
                            let ref f = el[0].clone();
                            let args = el[1..].to_vec();
                            match f {
                                Func(_, _) => f.apply(args),
                                MalFunc {
                                    ast: mast,
                                    env: menv,
                                    params,
                                    ..
                                } => {
                                    let a = &**mast;
                                    let p = &**params;
                                    env = env_bind(Some(menv.clone()), p.clone(), args)?;
                                    ast = a.clone();
                                    continue 'tco;
                                }
                                _ => error("attempt to call non-function"),
                            }
                        }
                        _ => error("expected a list"),
                    },
                }
            }
            _ => eval_ast(&ast, &env),
        };

        break;
    } // end 'tco loop

    ret
}