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use {LispResult, Error, Value, Type, Environment, EnvironmentStruct, Closure};
fn quasiquote(s: Value) -> Value {
match **s.clone() {
Type::List(ref v) if !v.is_empty() => {
match **v[0].clone() {
Type::Symbol(ref sym) if sym == "unquote" && v.len() >= 2 => {
return v[1].clone();
},
Type::List(ref v2) if v2.len() >= 2 => {
match **v2[0].clone() {
Type::Symbol(ref sym2) if sym2 == "splice-unquote" => {
return Value::list(vec![
Value::symbol("concat".to_owned()),
v2[1].clone(),
quasiquote(Value::list(v[1..].to_vec()))
]);
}
_ => return Value::list(vec![
Value::symbol("cons".to_owned()),
quasiquote(v[0].clone()),
quasiquote(Value::list(v[1..].to_vec()))
]),
}
}
_ => {
return Value::list(vec![
Value::symbol("cons".to_owned()),
quasiquote(v[0].clone()),
quasiquote(Value::list(v[1..].to_vec()))
]);
}
}
},
_ => return Value::list(vec![Value::symbol("quote".to_owned()), s]),
}
}
fn is_macro_call(ast: &Value, env: Environment) -> Option<Closure> {
if let Type::List(ref v) = ***ast {
if let Type::Symbol(ref sym) = **v[0] {
match env.borrow().get(sym.clone()) {
Ok(val) => if let Type::Closure(ref c) = **val {
if c.is_macro {
return Some(c.clone())
}
},
Err(_) => return None
}
}
}
None
}
fn macroexpand(mut ast: Value, mut env: Environment) -> LispResult {
while let Some(closure) = is_macro_call(&ast, env.clone()) {
match **ast.clone() {
Type::List(ref v) => {
let args = v[1..].to_vec();
let new_env = EnvironmentStruct::with_bindings(
Some(closure.env.clone()),
closure.binds.clone(),
args).map_err(Error::BindError)?;
ast = eval(closure.body.clone(), new_env.clone())?;
env = new_env.clone();
continue;
},
_ => unreachable!()
}
}
Ok(ast)
}
fn eval_ast(s: &Value, env: Environment) -> LispResult {
match ***s {
Type::Symbol(ref k) => env.borrow().get(k.clone()),
Type::List(ref v) => {
let mut result = Vec::new();
for e in v {
result.push(eval(e.clone(), env.clone())?);
}
Ok(Value::list(result))
},
Type::Vector(ref v) => {
let mut result = Vec::new();
for e in v {
result.push(eval(e.clone(), env.clone())?);
}
Ok(Value::vector(result))
},
Type::Map(ref m) => {
let mut result = m.clone();
for (k, v) in m {
result.insert(k.to_owned(), eval(v.clone(), env.clone())?);
}
Ok(Value::map(result))
},
_ => Ok(s.clone()),
}
}
pub fn eval(mut s: Value, mut env: Environment) -> LispResult {
loop {
s = macroexpand(s.clone(), env.clone())?;
match **s.clone() {
Type::List(ref v) => {
if v.is_empty() {
return Ok(s.clone());
}
match **v[0] {
Type::Symbol(ref sym) if sym == "def" => {
if v.len() != 3 {
return Err(Error::InvalidArity("def", "2"))
}
if let Type::Symbol(ref s) = **v[1] {
let val = eval(v[2].clone(), env.clone())?;
env.borrow_mut().set(s.clone(), val.clone());
return Ok(val.clone())
} else {
return Err(Error::InvalidArg("def", "symbol followed by any value"))
}
},
Type::Symbol(ref sym) if sym == "defmacro" => {
if v.len() != 4 {
return Err(Error::InvalidArity("defmacro!", "3"))
}
if let Type::Symbol(ref name) = **v[1] {
let closure = Value::list(vec![
Value::symbol("fn".into()),
v[2].clone(),
v[3].clone()]);
let val = eval(closure, env.clone())?;
if let Type::Closure(ref closure) = **val {
let macros = Value::macros(closure.clone());
env.borrow_mut().set(name.clone(), macros.clone());
return Ok(macros.clone());
}
}
return Err(Error::InvalidArg("defmacro", "symbol followed by list of symbols and any value"))
}
Type::Symbol(ref sym) if sym == "let" => {
if v.len() != 3 {
return Err(Error::InvalidArity("let", "2"))
}
let new_env = EnvironmentStruct::new(Some(env.clone()));
match **v[1] {
Type::Vector(ref v) | Type::List(ref v) => {
if v.len() % 2 != 0 {
return Err(Error::Custom("Bindings in 'let' aren't balanced".into()))
}
let mut it = v.iter();
while it.len() >= 2 {
let bind = it.next().unwrap();
let expr = it.next().unwrap();
if let Type::Symbol(ref b) = ***bind {
let e = eval(expr.clone(), new_env.clone())?;
new_env.borrow_mut().set(b.clone(),e);
}
}
},
_ => return Err(Error::InvalidArg("let", "vector or list of pairs (symbol, any value), followed by any value"))
}
s = v[2].clone();
env = new_env.clone();
continue;
},
Type::Symbol(ref sym) if sym == "do" => {
if v.len() == 1 {
return Err(Error::InvalidArity("do", ">= 1"))
}
let len = v.len() - 1;
for e in &v[1..len] {
let _ = eval(e.clone(), env.clone())?;
}
s = v[len].clone();
continue;
},
Type::Symbol(ref sym) if sym == "if" => {
if v.len() != 4 {
return Err(Error::InvalidArity("if", "3"))
}
let expr = eval(v[1].clone(), env.clone())?;
match **expr {
Type::List(ref vec) |
Type::Vector(ref vec) if vec.is_empty() => {
s = v[3].clone();
continue;
},
Type::Boolean(ref b) if b == &false => {
s = v[3].clone();
continue;
}
_ => {
s = v[2].clone();
continue;
}
}
},
Type::Symbol(ref sym) if sym == "eval" => {
if v.len() != 2 {
return Err(Error::InvalidArity("eval", "1"))
}
let ast = v[1].clone();
s = eval(ast, env.clone())?;
env = EnvironmentStruct::top(&env);
continue;
},
Type::Symbol(ref sym) if sym == "quote" => {
if v.len() == 1 {
return Err(Error::InvalidArity("quote", "> 1"))
}
return Ok(v[1].clone())
},
Type::Symbol(ref sym) if sym == "quasiquote" => {
if v.len() == 1 {
return Err(Error::InvalidArity("quasiquote", "> 1"))
}
s = quasiquote(v[1].clone());
continue;
}
Type::Symbol(ref sym) if sym == "macroexpand" => {
if v.len() != 2 {
return Err(Error::InvalidArity("macroexpand", "1"))
}
return macroexpand(v[1].clone(), env.clone());
}
Type::Symbol(ref sym) if sym == "fn" => {
if v.len() != 3 {
return Err(Error::InvalidArity("fn", "2"))
}
let binds = match **v[1].clone() {
Type::List(ref v) => {
let mut result = Vec::new();
for e in v {
if let Type::Symbol(ref sym) = ***e {
result.push(sym.clone());
} else {
return Err(Error::InvalidArg("fn", "list of symbols followed by any value"))
}
}
result
},
_ => return Err(Error::InvalidArg("fn", "list of symbols followed by any value"))
};
let body = (**v[2]).clone();
return Ok(Value::closure(binds, Value::new(body), env.clone()));
},
Type::Symbol(ref sym) if sym == "throw" => {
if v.len() != 2 {
return Err(Error::InvalidArity("throw", "1"))
}
return Err(Error::Value(v[1].clone()))
},
Type::Symbol(ref sym) if sym == "try" => {
if v.len() != 3 {
return Err(Error::InvalidArity("try", "2"))
}
let err_val = match eval(v[1].clone(), env.clone()) {
ok @ Ok(_) => return ok,
Err(e) => match e {
Error::Value(value) => value.clone(),
any => Value::string(any.to_string()),
}
};
if let Type::List(ref list) = **v[2] {
if let Type::Symbol(ref sym) = **list[0] {
if sym != "catch" {
return Err(Error::InvalidArg("try", "any value followed by catch function"))
}
}
if list.len() != 3 {
return Err(Error::InvalidArity("catch", "2"))
}
if let Type::Symbol(ref bind_sym) = **list[1] {
let new_env =EnvironmentStruct::with_bindings(
Some(env.clone()),
vec![bind_sym.clone()],
vec![err_val]
).map_err(Error::BindError)?;
s = list[2].clone();
env = new_env;
continue;
} else {
return Err(Error::InvalidArg("catch", "symbol followed by any value"))
}
}
}
_ => {
let evaluated = eval_ast(&s, env.clone())?;
match **evaluated {
Type::List(ref v) => {
let args = v[1..].to_vec();
match **v[0].clone() {
Type::Func(func) => return func(args),
Type::Closure(ref closure) => {
let new_env = EnvironmentStruct::with_bindings(
Some(closure.env.clone()),
closure.binds.clone(),
args
).map_err(Error::BindError)?;
s = closure.body.clone();
env = new_env.clone();
continue;
}
_ => return Err(Error::Custom("Attempt to call not a funtion".into()))
}
},
_ => unreachable!(),
}
},
}
},
_ => return eval_ast(&s, env),
}
}
}