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use std::collections::HashMap; use expr::{ Arguments, Expr::{self, *}, Function, }; type Data = HashMap<String, Expr>; #[derive(Debug)] pub struct Env { stack: Vec<Data>, } impl Env { pub fn new() -> Self { let mut e = Env { stack: vec![HashMap::new()], }; e.initialize(); e } fn initialize(&mut self) { self.insert( "+".to_string(), Fun(Function::Builtin(add), Arguments::Variadic), ); self.insert( "-".to_string(), Fun(Function::Builtin(sub), Arguments::Variadic), ); self.insert( "*".to_string(), Fun(Function::Builtin(mul), Arguments::Variadic), ); self.insert( "/".to_string(), Fun(Function::Builtin(div), Arguments::Variadic), ); self.insert( "=".to_string(), Fun(Function::Builtin(eq), Arguments::Variadic), ); self.insert( "if".to_string(), Special( Function::Builtin(iff), Arguments::Fixed(vec![ "cond".to_string(), "expr1".to_string(), "expr2".to_string(), ]), ), ); self.insert( "lambda".to_string(), Special( Function::Builtin(lambda), Arguments::Fixed(vec!["args".to_string(), "body".to_string()]), ), ); self.insert( "set".to_string(), Fun( Function::Builtin(set), Arguments::Fixed(vec!["name".to_string(), "value".to_string()]), ), ); } pub fn eval(&mut self, value: &Expr) -> Expr { match value { Nil => Nil, Int(x) => Int(*x), Float(x) => Float(*x), Bool(x) => Bool(*x), Str(x) => Str(x.clone()), Symbol(x) => self.get(x.clone()).unwrap_or(Nil), Quote(x) => *x.clone(), Fun(f, args) => Fun(f.clone(), args.clone()), Special(f, args) => Fun(f.clone(), args.clone()), List(list) => self.eval_list(list), } } pub fn insert_parent(&mut self, key: String, value: Expr) { self.stack[0].insert(key, value); } pub fn insert(&mut self, key: String, value: Expr) { let index = self.stack.len() - 1; self.stack[index].insert(key, value); } pub fn get(&self, key: String) -> Option<Expr> { for data in self.stack.iter().rev() { if data.contains_key(&key) { return data.get(&key).cloned(); } } None } fn enter(&mut self) { self.stack.push(HashMap::new()) } fn exit(&mut self) { self.stack .pop() .expect("Attempted to pop empty environment stack"); } fn eval_list(&mut self, list: &Vec<Expr>) -> Expr { match &list[..] { [expr, rest..] => match self.eval(expr) { Fun(fun, arg_names) => { let mut evaluated_args: Vec<Expr> = vec![]; self.enter(); for expr in rest.iter() { evaluated_args.push(self.eval(expr)); } self.bind_args(evaluated_args, arg_names.clone()); let result = self.eval_fun(fun.clone()); self.exit(); result } Special(fun, arg_names) => { self.enter(); self.bind_args(rest.to_vec(), arg_names.clone()); let result = self.eval_fun(fun.clone()); self.exit(); result } other => panic!("Can't apply {:?}", other), }, [] => Nil, } } fn eval_fun(&mut self, fun: Function) -> Expr { match fun { Function::Builtin(builtin) => builtin(self), Function::Dynamic(expr) => self.eval(&expr), } } fn bind_args(&mut self, exprs: Vec<Expr>, args: Arguments) { match args { Arguments::Variadic => self.insert("varargs".to_string(), List(exprs)), Arguments::Fixed(names) => { if exprs.len() != names.len() { panic!("Wrong argument count"); } for (expr, name) in exprs.iter().zip(names) { self.insert(name, expr.clone()); } } } } } fn add(env: &mut Env) -> Expr { if let Some(List(args)) = env.get("varargs".to_string()) { args.iter().fold(Int(0), |acc, x| acc + x.clone()) } else { panic!("could not fetch arguments"); } } fn sub(env: &mut Env) -> Expr { if let Some(List(args)) = env.get("varargs".to_string()) { match &args[..] { [x] => Int(0) - x.clone(), [head, tail..] => tail.iter().fold(head.clone(), |acc, x| acc - x.clone()), [] => panic!("sub requires at least one argument"), } } else { panic!("could not fetch arguments"); } } fn mul(env: &mut Env) -> Expr { if let Some(List(args)) = env.get("varargs".to_string()) { args.iter().fold(Int(1), |acc, x| acc * x.clone()) } else { panic!("could not fetch arguments"); } } fn div(env: &mut Env) -> Expr { if let Some(List(args)) = env.get("varargs".to_string()) { match &args[..] { [head] => Int(1) / head.clone(), [head, tail..] => tail.iter().fold(head.clone(), |acc, x| acc / x.clone()), [] => panic!("div requires at least one argument"), } } else { panic!("could not fetch arguments"); } } fn iff(env: &mut Env) -> Expr { match ( env.get("cond".to_string()).and_then(|e| Some(env.eval(&e))), env.get("expr1".to_string()), env.get("expr2".to_string()), ) { (Some(cond), Some(expr1), Some(expr2)) => match cond { Bool(true) => env.eval(&expr1), Bool(false) => env.eval(&expr2), _ => panic!("not a bool"), }, _ => panic!("ass"), } } fn eq(env: &mut Env) -> Expr { if let Some(List(args)) = env.get("varargs".to_string()) { match &args[..] { [_head] => Bool(true), [head, tail..] => Bool(tail.iter().all(|ref x| *x == head)), [] => panic!("eq requires a at least one argument"), } } else { panic!("eq requires a at least one argument") } } fn lambda(env: &mut Env) -> Expr { let body = env.get("body".to_string()).unwrap(); match env.get("args".to_string()).unwrap() { List(args) => { let arguments = Arguments::Fixed( args.iter() .map(|arg| match arg { Symbol(s) => s.clone(), _ => panic!("lambda arguments must be symbols"), }) .collect::<Vec<_>>(), ); Fun(Function::Dynamic(Box::new(body)), arguments) } _ => panic!("This should not happen"), } } fn set(env: &mut Env) -> Expr { match ( env.get("name".to_string()).unwrap(), env.get("value".to_string()).unwrap(), ) { (Symbol(s), expr) => { env.insert_parent(s, expr.clone()); expr } (other, _) => panic!("Variable name is not a symbol: {:?}", other), } }