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extern crate hyoka;
#[derive(Debug, Clone)]
struct Env {
global: std::collections::HashMap<String, Expression>,
}
impl Env {
pub fn new() -> Self {
Env {
global: std::collections::HashMap::new(),
}
}
}
#[derive(Debug, Clone, PartialEq)]
enum Expression {
Float(f32),
Symbol(String),
List(Vec<Expression>),
// (Parameters, Body)
Procedure(Vec<Expression>, Vec<Expression>),
}
impl From<&str> for Expression {
fn from(value: &str) -> Self {
if let Ok(v) = value.parse::<f32>() {
Expression::Float(v)
} else {
Expression::Symbol(String::from(value))
}
}
}
impl Expression {
pub fn parse(tokens: &mut Vec<String>) -> Result<Expression, String> {
if tokens.len() == 0 {
Err(format!("unexpected EOF while parsing the tokens."))
} else {
let token = tokens.remove(0);
match token.as_str() {
"(" => {
// TODO: Can we avoid ITM here?
let mut list = Vec::<Expression>::new();
while tokens.len() != 1 && tokens[0] != ")" {
match Expression::parse(tokens) {
Ok(v) => list.push(v),
Err(e) => {
return Err(e);
}
}
}
if tokens.len() == 1 && tokens[0] == ")" {
tokens.remove(0);
Ok(Expression::List(list))
} else {
Err(format!("Malformed expression. Insufficient closing ')'"))
}
}
")" => Err(format!("unexpected ')' found while parsing tokens")),
_ => Ok(Expression::from(token.as_str())),
}
}
}
pub fn evaluate(&self, env: &mut Env) -> Option<Expression> {
match self.clone() {
Expression::Float(_) => Some(self.clone()),
Expression::Symbol(name) => {
match env.global.get(&name) {
Some(Expression::Float(x)) => Some(Expression::Float(*x)),
Some(Expression::Symbol(x)) => {
let s = Expression::Symbol(x.clone());
// NOTE: This could potentially introduce infinite loop...
s.evaluate(env)
}
Some(Expression::List(list)) => {
let s = Expression::List(list.clone());
// NOTE: This could potentially introduce infinite loop...
s.evaluate(env)
}
// NOTE: WTF Was I trying to do here????
Some(Expression::Procedure(parameter_symbols, body)) => Some(
Expression::Procedure(parameter_symbols.clone(), body.clone()),
),
None => Some(Expression::Symbol(name.clone())),
}
}
Expression::List(mut list) => {
match list.as_mut_slice() {
[Expression::Symbol(procedure_name), args @ ..] => {
match procedure_name.as_str() {
// TODO: Make this a macro...
"+" => {
let result = args.iter_mut().fold(0.0f32, |acc, x| {
if let Some(Expression::Float(x)) = x.evaluate(env) {
acc + x
} else {
acc
}
});
Some(Expression::Float(result))
}
"-" => {
let result = args.iter_mut().fold(0.0f32, |acc, x| {
if let Some(Expression::Float(x)) = x.evaluate(env) {
acc - x
} else {
acc
}
});
Some(Expression::Float(result))
}
"*" => {
let result = args.iter_mut().fold(1.0f32, |acc, x| {
if let Some(Expression::Float(x)) = x.evaluate(env) {
acc * x
} else {
acc
}
});
Some(Expression::Float(result))
}
"/" => {
let result = args.iter_mut().fold(1.0f32, |acc, x| {
if let Some(Expression::Float(x)) = x.evaluate(env) {
acc / x
} else {
acc
}
});
Some(Expression::Float(result))
}
"lambda" => {
if let [_, Expression::List(params), Expression::List(body)] =
list.as_slice()
{
Some(Expression::Procedure(params.clone(), body.clone()))
} else {
None
}
}
"define" => {
if let [_, Expression::Symbol(name), expression] = list.as_slice() {
if let Some(evaluation) = expression.evaluate(env) {
env.global.insert(name.clone(), evaluation);
}
}
None
}
name => {
if let Some(Expression::Procedure(parameter, body)) =
env.global.get(name)
{
if parameter.len() == args.len() {
let mut env = env.clone();
let mut local_env = args.iter().zip(parameter.iter()).fold(
Env::new(),
|mut local_env, (arg_body, arg_symbol)| {
let value = arg_body.evaluate(&mut env).unwrap();
if let Expression::Symbol(arg_symbol) = arg_symbol {
local_env
.global
.insert(arg_symbol.clone(), value);
}
local_env
},
);
let procedure_call = Expression::List(body.clone());
procedure_call.evaluate(&mut local_env)
} else {
None
}
} else {
None
}
}
}
}
[..] => None,
}
}
// NOTE: What _should_ happen here?
Expression::Procedure(_, _) => None,
}
}
}
pub fn main() {
let mut repl = hyoka::Repl::new("lisp>", Env::new(), |env: &mut Env, y: String| {
let mut y = y
.replace('(', " ( ")
.replace(')', " ) ")
.split_ascii_whitespace()
.map(String::from)
.collect::<Vec<String>>();
let result = if let Ok(Some(Expression::Float(result))) = Expression::parse(&mut y)
.map(|x| x.evaluate(env))
.map_err(|x| {
println!("error:{}", x);
}) {
Some(format!("{}", result))
} else {
None
};
result
});
repl.run();
}