pub struct Env { /* private fields */ }Expand description
An environment of symbol bindings. Used for the base environment, for
closures, for let statements, for function arguments, etc.
Implementations§
source§impl Env
impl Env
sourcepub fn new() -> Self
pub fn new() -> Self
Create a new, empty environment
Examples found in repository?
src/default_environment.rs (line 19)
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pub fn default_env() -> Env {
let mut env = Env::new();
env.define(
Symbol::from("print"),
Value::NativeFunc(|_env, args| {
let expr = require_arg("print", &args, 0)?;
println!("{}", &expr);
Ok(expr.clone())
}),
);
env.define(
Symbol::from("is_null"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_null", &args, 0)?;
Ok(Value::from(*val == Value::NIL))
}),
);
env.define(
Symbol::from("is_number"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_number", &args, 0)?;
Ok(match val {
Value::Int(_) => Value::True,
Value::Float(_) => Value::True,
_ => Value::NIL,
})
}),
);
env.define(
Symbol::from("is_symbol"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_symbol", &args, 0)?;
Ok(match val {
Value::Symbol(_) => Value::True,
_ => Value::NIL,
})
}),
);
env.define(
Symbol::from("is_boolean"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_boolean", &args, 0)?;
Ok(match val {
Value::True => Value::True,
Value::False => Value::True,
_ => Value::NIL,
})
}),
);
env.define(
Symbol::from("is_procedure"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_procedure", &args, 0)?;
Ok(match val {
Value::Lambda(_) => Value::True,
Value::NativeFunc(_) => Value::True,
_ => Value::NIL,
})
}),
);
env.define(
Symbol::from("is_pair"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_pair", &args, 0)?;
Ok(match val {
Value::List(_) => Value::True,
_ => Value::NIL,
})
}),
);
env.define(
Symbol::from("car"),
Value::NativeFunc(|_env, args| {
let list = require_typed_arg::<&List>("car", &args, 0)?;
list.car()
}),
);
env.define(
Symbol::from("cdr"),
Value::NativeFunc(|_env, args| {
let list = require_typed_arg::<&List>("cdr", &args, 0)?;
Ok(Value::List(list.cdr()))
}),
);
env.define(
Symbol::from("cons"),
Value::NativeFunc(|_env, args| {
let car = require_arg("cons", &args, 0)?;
let cdr = require_typed_arg::<&List>("cons", &args, 1)?;
Ok(Value::List(cdr.cons(car.clone())))
}),
);
env.define(
Symbol::from("list"),
Value::NativeFunc(|_env, args| Ok(Value::List(args.iter().collect::<List>()))),
);
env.define(
Symbol::from("nth"),
Value::NativeFunc(|_env, args| {
let index = require_typed_arg::<IntType>("nth", &args, 0)?;
let list = require_typed_arg::<&List>("nth", &args, 1)?;
let index = TryInto::<usize>::try_into(index).map_err(|_| RuntimeError {
msg: "Failed converting to `usize`".to_owned(),
})?;
Ok(list.into_iter().nth(index).unwrap_or(Value::NIL))
}),
);
env.define(
Symbol::from("sort"),
Value::NativeFunc(|_env, args| {
let list = require_typed_arg::<&List>("sort", &args, 0)?;
let mut v: Vec<Value> = list.into_iter().collect();
v.sort();
Ok(Value::List(v.into_iter().collect()))
}),
);
env.define(
Symbol::from("reverse"),
Value::NativeFunc(|_env, args| {
let list = require_typed_arg::<&List>("reverse", &args, 0)?;
let mut v: Vec<Value> = list.into_iter().collect();
v.reverse();
Ok(Value::List(v.into_iter().collect()))
}),
);
env.define(
Symbol::from("map"),
Value::NativeFunc(|env, args| {
let func = require_arg("map", &args, 0)?;
let list = require_typed_arg::<&List>("map", &args, 1)?;
list.into_iter()
.map(|val| {
let expr = lisp! { ({func.clone()} (quote {val})) };
eval(env.clone(), &expr)
})
.collect::<Result<List, RuntimeError>>()
.map(Value::List)
}),
);
// 🦀 Oh the poor `filter`, you must feel really sad being unused.
env.define(
Symbol::from("filter"),
Value::NativeFunc(|env, args| {
let func = require_arg("filter", &args, 0)?;
let list = require_typed_arg::<&List>("filter", &args, 1)?;
list.into_iter()
.filter_map(|val: Value| -> Option<Result<Value, RuntimeError>> {
let expr = lisp! { ({func.clone()} (quote {val.clone()})) };
match eval(env.clone(), &expr) {
Ok(matches) => {
if matches.into() {
Some(Ok(val))
} else {
None
}
}
Err(e) => Some(Err(e)),
}
})
.collect::<Result<List, RuntimeError>>()
.map(Value::List)
}),
);
env.define(
Symbol::from("length"),
Value::NativeFunc(|_env, args| {
let list = require_typed_arg::<&List>("length", &args, 0)?;
cfg_if! {
if #[cfg(feature = "bigint")] {
Ok(Value::Int(list.into_iter().len().into()))
} else {
Ok(Value::Int(list.into_iter().len() as IntType))
}
}
}),
);
env.define(
Symbol::from("range"),
Value::NativeFunc(|_env, args| {
let start = require_typed_arg::<IntType>("range", &args, 0)?;
let end = require_typed_arg::<IntType>("range", &args, 1)?;
let mut current = start;
Ok(Value::List(
std::iter::from_fn(move || {
if current == end {
None
} else {
let res = Some(current.clone());
current += 1;
res
}
})
.map(Value::from)
.collect(),
))
}),
);
env.define(
Symbol::from("hash"),
Value::NativeFunc(|_env, args| {
let chunks = args.chunks(2);
let mut hash = HashMap::new();
for pair in chunks {
let key = pair.get(0).unwrap();
let value = pair.get(1);
if let Some(value) = value {
hash.insert(key.clone(), value.clone());
} else {
return Err(RuntimeError {
msg: format!("Must pass an even number of arguments to 'hash', because they're used as key/value pairs; found extra argument {}", key)
});
}
}
Ok(Value::HashMap(Rc::new(RefCell::new(hash))))
}),
);
env.define(
Symbol::from("hash_get"),
Value::NativeFunc(|_env, args| {
let hash = require_typed_arg::<&HashMapRc>("hash_get", &args, 0)?;
let key = require_arg("hash_get", &args, 1)?;
Ok(hash
.borrow()
.get(key)
.map(|v| v.clone())
.unwrap_or(Value::NIL))
}),
);
env.define(
Symbol::from("hash_set"),
Value::NativeFunc(|_env, args| {
let hash = require_typed_arg::<&HashMapRc>("hash_set", &args, 0)?;
let key = require_arg("hash_set", &args, 1)?;
let value = require_arg("hash_set", &args, 2)?;
hash.borrow_mut().insert(key.clone(), value.clone());
Ok(Value::HashMap(hash.clone()))
}),
);
env.define(
Symbol::from("+"),
Value::NativeFunc(|_env, args| {
let first_arg = require_arg("+", &args, 1)?;
let mut total = match first_arg {
Value::Int(_) => Ok(Value::Int(0.into())),
Value::Float(_) => Ok(Value::Float(0.0)),
Value::String(_) => Ok(Value::String("".into())),
_ => Err(RuntimeError {
msg: format!(
"Function \"+\" requires arguments to be numbers or strings; found {}",
first_arg
),
}),
}?;
for arg in args {
total = (&total + &arg).map_err(|_| RuntimeError {
msg: format!(
"Function \"+\" requires arguments to be numbers or strings; found {}",
arg
),
})?;
}
Ok(total)
}),
);
env.define(
Symbol::from("-"),
Value::NativeFunc(|_env, args| {
let a = require_arg("-", &args, 0)?;
let b = require_arg("-", &args, 1)?;
(a - b).map_err(|_| RuntimeError {
msg: String::from("Function \"-\" requires arguments to be numbers"),
})
}),
);
env.define(
Symbol::from("*"),
Value::NativeFunc(|_env, args| {
let mut product = Value::Int(1.into());
for arg in args {
product = (&product * &arg).map_err(|_| RuntimeError {
msg: format!(
"Function \"*\" requires arguments to be numbers; found {}",
arg
),
})?;
}
Ok(product)
}),
);
env.define(
Symbol::from("/"),
Value::NativeFunc(|_env, args| {
let a = require_arg("/", &args, 0)?;
let b = require_arg("/", &args, 1)?;
(a / b).map_err(|_| RuntimeError {
msg: String::from("Function \"/\" requires arguments to be numbers"),
})
}),
);
env.define(
Symbol::from("truncate"),
Value::NativeFunc(|_env, args| {
let a = require_arg("truncate", &args, 0)?;
let b = require_arg("truncate", &args, 1)?;
if let (Ok(a), Ok(b)) = (
TryInto::<IntType>::try_into(a),
TryInto::<IntType>::try_into(b),
) {
return Ok(Value::Int(a / b));
}
Err(RuntimeError {
msg: String::from("Function \"truncate\" requires arguments to be integers"),
})
}),
);
env.define(
Symbol::from("not"),
Value::NativeFunc(|_env, args| {
let a = require_arg("not", &args, 0)?;
let a: bool = a.into();
Ok(Value::from(!a))
}),
);
env.define(
Symbol::from("=="),
Value::NativeFunc(|_env, args| {
let a = require_arg("==", &args, 0)?;
let b = require_arg("==", &args, 1)?;
Ok(Value::from(a == b))
}),
);
env.define(
Symbol::from("!="),
Value::NativeFunc(|_env, args| {
let a = require_arg("!=", &args, 0)?;
let b = require_arg("!=", &args, 1)?;
Ok(Value::from(a != b))
}),
);
env.define(
Symbol::from("<"),
Value::NativeFunc(|_env, args| {
let a = require_arg("<", &args, 0)?;
let b = require_arg("<", &args, 1)?;
Ok(Value::from(a < b))
}),
);
env.define(
Symbol::from("<="),
Value::NativeFunc(|_env, args| {
let a = require_arg("<=", &args, 0)?;
let b = require_arg("<=", &args, 1)?;
Ok(Value::from(a <= b))
}),
);
env.define(
Symbol::from(">"),
Value::NativeFunc(|_env, args| {
let a = require_arg(">", &args, 0)?;
let b = require_arg(">", &args, 1)?;
Ok(Value::from(a > b))
}),
);
env.define(
Symbol::from(">="),
Value::NativeFunc(|_env, args| {
let a = require_arg(">=", &args, 0)?;
let b = require_arg(">=", &args, 1)?;
Ok(Value::from(a >= b))
}),
);
env.define(
Symbol::from("eval"),
Value::NativeFunc(|env, args| {
let expr = require_arg("eval", &args, 0)?;
eval(env, expr)
}),
);
env.define(
Symbol::from("apply"),
Value::NativeFunc(|env, args| {
let func = require_arg("apply", &args, 0)?;
let params = require_typed_arg::<&List>("apply", &args, 1)?;
eval(env, &Value::List(params.cons(func.clone())))
}),
);
env
}sourcepub fn extend(parent: Rc<RefCell<Env>>) -> Self
pub fn extend(parent: Rc<RefCell<Env>>) -> Self
Create a new environment extending the given environment
Examples found in repository?
src/interpreter.rs (line 168)
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fn eval_inner(
env: Rc<RefCell<Env>>,
expression: &Value,
context: Context,
) -> Result<Value, RuntimeError> {
if context.quoting {
match expression {
Value::List(list) if *list != List::NIL => match &list.car()? {
Value::Symbol(Symbol(keyword)) if keyword == "comma" => {
// do nothing, handle it down below
}
_ => {
return list
.into_iter()
.map(|el| eval_inner(env.clone(), &el, context))
.collect::<Result<List, RuntimeError>>()
.map(Value::List);
}
},
_ => return Ok(expression.clone()),
}
}
match expression {
// look up symbol
Value::Symbol(symbol) => env.borrow().get(symbol).ok_or_else(|| RuntimeError {
msg: format!("\"{}\" is not defined", symbol),
}),
// s-expression
Value::List(list) if *list != List::NIL => {
match &list.car()? {
// special forms
Value::Symbol(Symbol(keyword)) if keyword == "comma" => {
eval_inner(env, &list.cdr().car()?, context.quoting(false))
}
Value::Symbol(Symbol(keyword)) if keyword == "quote" => {
eval_inner(env, &list.cdr().car()?, context.quoting(true))
}
Value::Symbol(Symbol(keyword)) if keyword == "define" || keyword == "set" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let value_expr = require_arg(keyword, args, 1)?;
let value = eval_inner(env.clone(), value_expr, context.found_tail(true))?;
if keyword == "define" {
env.borrow_mut().define(symbol.clone(), value.clone());
} else {
env.borrow_mut().set(symbol.clone(), value.clone())?;
}
Ok(value)
}
Value::Symbol(Symbol(keyword)) if keyword == "defmacro" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let argnames_list = require_typed_arg::<&List>(keyword, args, 1)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr().cdr()));
let lambda = Value::Macro(Lambda {
closure: env.clone(),
argnames,
body,
});
env.borrow_mut().define(symbol.clone(), lambda);
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "defun" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let argnames_list = require_typed_arg::<&List>(keyword, args, 1)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr().cdr()));
let lambda = Value::Lambda(Lambda {
closure: env.clone(),
argnames,
body,
});
env.borrow_mut().define(symbol.clone(), lambda);
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "lambda" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let argnames_list = require_typed_arg::<&List>(keyword, args, 0)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr()));
Ok(Value::Lambda(Lambda {
closure: env,
argnames,
body,
}))
}
Value::Symbol(Symbol(keyword)) if keyword == "let" => {
let let_env = Rc::new(RefCell::new(Env::extend(env)));
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let declarations = require_typed_arg::<&List>(keyword, args, 0)?;
for decl in declarations.into_iter() {
let decl = &decl;
let decl_cons: &List = decl.try_into().map_err(|_| RuntimeError {
msg: format!("Expected declaration clause, found {}", decl),
})?;
let symbol = &decl_cons.car()?;
let symbol: &Symbol = symbol.try_into().map_err(|_| RuntimeError {
msg: format!("Expected symbol for let declaration, found {}", symbol),
})?;
let expr = &decl_cons.cdr().car()?;
let result = eval_inner(let_env.clone(), expr, context.found_tail(true))?;
let_env.borrow_mut().define(symbol.clone(), result);
}
let body = &Value::List(list.cdr().cdr());
let body: &List = body.try_into().map_err(|_| RuntimeError {
msg: format!(
"Expected expression(s) after let-declarations, found {}",
body
),
})?;
eval_block_inner(let_env, body.into_iter(), context)
}
Value::Symbol(Symbol(keyword)) if keyword == "begin" => {
eval_block_inner(env, list.cdr().into_iter(), context)
}
Value::Symbol(Symbol(keyword)) if keyword == "cond" => {
let clauses = list.cdr();
for clause in clauses.into_iter() {
let clause = &clause;
let clause: &List = clause.try_into().map_err(|_| RuntimeError {
msg: format!("Expected conditional clause, found {}", clause),
})?;
let condition = &clause.car()?;
let then = &clause.cdr().car()?;
if eval_inner(env.clone(), condition, context.found_tail(true))?.into() {
return eval_inner(env, then, context);
}
}
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "if" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let condition = require_arg(keyword, args, 0)?;
let then_expr = require_arg(keyword, args, 1)?;
let else_expr = require_arg(keyword, args, 2).ok();
if eval_inner(env.clone(), condition, context.found_tail(true))?.into() {
eval_inner(env, then_expr, context)
} else {
else_expr
.map(|expr| eval_inner(env, &expr, context))
.unwrap_or(Ok(Value::NIL))
}
}
Value::Symbol(Symbol(keyword)) if keyword == "and" || keyword == "or" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let is_or = keyword.as_str() == "or";
let mut last_result: Option<Value> = None;
for arg in args {
let result = eval_inner(env.clone(), arg, context.found_tail(true))?;
let truthy: bool = (&result).into();
if is_or == truthy {
return Ok(result);
}
last_result = Some(result);
}
Ok(if let Some(last_result) = last_result {
last_result
} else {
// there were zero arguments
(!is_or).into()
})
}
// function call or macro expand
_ => {
let mut func_or_macro =
eval_inner(env.clone(), &list.car()?, context.found_tail(true))?;
if matches!(func_or_macro, Value::Macro(_)) {
let args = list.into_iter().skip(1).collect::<Vec<Value>>();
let expanded =
call_function_or_macro(env.clone(), &mut func_or_macro, args)?;
eval_inner(env.clone(), &expanded, Context::new())
} else {
let args = list
.into_iter()
.skip(1)
.map(|car| eval_inner(env.clone(), &car, context.found_tail(true)))
.collect::<Result<Vec<Value>, RuntimeError>>()?;
if !context.found_tail && context.in_func {
Ok(Value::TailCall {
func: Rc::new(func_or_macro),
args,
})
} else {
let mut res =
call_function_or_macro(env.clone(), &mut func_or_macro, args);
while let Ok(Value::TailCall { func, args }) = res {
res = call_function_or_macro(env.clone(), func.as_ref(), args);
}
res
}
}
}
}
}
// plain value
_ => Ok(expression.clone()),
}
}
// 🦀 Boo! Did I scare ya? Haha!
fn value_to_argnames(argnames: List) -> Result<Vec<Symbol>, RuntimeError> {
argnames
.into_iter()
.enumerate()
.map(|(index, arg)| match arg {
Value::Symbol(s) => Ok(s),
_ => Err(RuntimeError {
msg: format!(
"Expected list of arg names, but arg {} is a {}",
index,
arg.type_name()
),
}),
})
.collect()
}
/// Calling a function is separated from the main `eval_inner()` function
/// so that tail calls can be evaluated without just returning themselves
/// as-is as a tail-call.
fn call_function_or_macro(
env: Rc<RefCell<Env>>,
func: &Value,
args: Vec<Value>,
) -> Result<Value, RuntimeError> {
if let Value::NativeFunc(func) = func {
func(env, args)
} else if let Value::NativeClosure(closure) = func {
closure.borrow_mut()(env, args)
} else {
let lambda = match func {
Value::Lambda(lamb) => Some(lamb),
Value::Macro(lamb) => Some(lamb),
_ => None,
};
if let Some(lambda) = lambda {
// bind args
let mut arg_env = Env::extend(lambda.closure.clone());
for (index, arg_name) in lambda.argnames.iter().enumerate() {
if arg_name.0 == "..." {
// rest parameters
arg_env.define(
Symbol::from("..."),
Value::List(args.into_iter().skip(index).collect()),
);
break;
} else {
arg_env.define(arg_name.clone(), args[index].clone());
}
}
// evaluate each line of body
let clauses: &List = lambda.body.as_ref().try_into()?;
eval_block_inner(
Rc::new(RefCell::new(arg_env)),
clauses.into_iter(),
Context {
found_tail: false,
in_func: true,
quoting: false,
},
)
} else {
Err(RuntimeError {
msg: format!("{} is not callable", func),
})
}
}
}sourcepub fn get(&self, key: &Symbol) -> Option<Value>
pub fn get(&self, key: &Symbol) -> Option<Value>
Walks up the environment hierarchy until it finds the symbol’s value or runs out of environments.
Examples found in repository?
More examples
src/interpreter.rs (line 82)
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fn eval_inner(
env: Rc<RefCell<Env>>,
expression: &Value,
context: Context,
) -> Result<Value, RuntimeError> {
if context.quoting {
match expression {
Value::List(list) if *list != List::NIL => match &list.car()? {
Value::Symbol(Symbol(keyword)) if keyword == "comma" => {
// do nothing, handle it down below
}
_ => {
return list
.into_iter()
.map(|el| eval_inner(env.clone(), &el, context))
.collect::<Result<List, RuntimeError>>()
.map(Value::List);
}
},
_ => return Ok(expression.clone()),
}
}
match expression {
// look up symbol
Value::Symbol(symbol) => env.borrow().get(symbol).ok_or_else(|| RuntimeError {
msg: format!("\"{}\" is not defined", symbol),
}),
// s-expression
Value::List(list) if *list != List::NIL => {
match &list.car()? {
// special forms
Value::Symbol(Symbol(keyword)) if keyword == "comma" => {
eval_inner(env, &list.cdr().car()?, context.quoting(false))
}
Value::Symbol(Symbol(keyword)) if keyword == "quote" => {
eval_inner(env, &list.cdr().car()?, context.quoting(true))
}
Value::Symbol(Symbol(keyword)) if keyword == "define" || keyword == "set" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let value_expr = require_arg(keyword, args, 1)?;
let value = eval_inner(env.clone(), value_expr, context.found_tail(true))?;
if keyword == "define" {
env.borrow_mut().define(symbol.clone(), value.clone());
} else {
env.borrow_mut().set(symbol.clone(), value.clone())?;
}
Ok(value)
}
Value::Symbol(Symbol(keyword)) if keyword == "defmacro" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let argnames_list = require_typed_arg::<&List>(keyword, args, 1)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr().cdr()));
let lambda = Value::Macro(Lambda {
closure: env.clone(),
argnames,
body,
});
env.borrow_mut().define(symbol.clone(), lambda);
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "defun" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let argnames_list = require_typed_arg::<&List>(keyword, args, 1)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr().cdr()));
let lambda = Value::Lambda(Lambda {
closure: env.clone(),
argnames,
body,
});
env.borrow_mut().define(symbol.clone(), lambda);
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "lambda" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let argnames_list = require_typed_arg::<&List>(keyword, args, 0)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr()));
Ok(Value::Lambda(Lambda {
closure: env,
argnames,
body,
}))
}
Value::Symbol(Symbol(keyword)) if keyword == "let" => {
let let_env = Rc::new(RefCell::new(Env::extend(env)));
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let declarations = require_typed_arg::<&List>(keyword, args, 0)?;
for decl in declarations.into_iter() {
let decl = &decl;
let decl_cons: &List = decl.try_into().map_err(|_| RuntimeError {
msg: format!("Expected declaration clause, found {}", decl),
})?;
let symbol = &decl_cons.car()?;
let symbol: &Symbol = symbol.try_into().map_err(|_| RuntimeError {
msg: format!("Expected symbol for let declaration, found {}", symbol),
})?;
let expr = &decl_cons.cdr().car()?;
let result = eval_inner(let_env.clone(), expr, context.found_tail(true))?;
let_env.borrow_mut().define(symbol.clone(), result);
}
let body = &Value::List(list.cdr().cdr());
let body: &List = body.try_into().map_err(|_| RuntimeError {
msg: format!(
"Expected expression(s) after let-declarations, found {}",
body
),
})?;
eval_block_inner(let_env, body.into_iter(), context)
}
Value::Symbol(Symbol(keyword)) if keyword == "begin" => {
eval_block_inner(env, list.cdr().into_iter(), context)
}
Value::Symbol(Symbol(keyword)) if keyword == "cond" => {
let clauses = list.cdr();
for clause in clauses.into_iter() {
let clause = &clause;
let clause: &List = clause.try_into().map_err(|_| RuntimeError {
msg: format!("Expected conditional clause, found {}", clause),
})?;
let condition = &clause.car()?;
let then = &clause.cdr().car()?;
if eval_inner(env.clone(), condition, context.found_tail(true))?.into() {
return eval_inner(env, then, context);
}
}
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "if" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let condition = require_arg(keyword, args, 0)?;
let then_expr = require_arg(keyword, args, 1)?;
let else_expr = require_arg(keyword, args, 2).ok();
if eval_inner(env.clone(), condition, context.found_tail(true))?.into() {
eval_inner(env, then_expr, context)
} else {
else_expr
.map(|expr| eval_inner(env, &expr, context))
.unwrap_or(Ok(Value::NIL))
}
}
Value::Symbol(Symbol(keyword)) if keyword == "and" || keyword == "or" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let is_or = keyword.as_str() == "or";
let mut last_result: Option<Value> = None;
for arg in args {
let result = eval_inner(env.clone(), arg, context.found_tail(true))?;
let truthy: bool = (&result).into();
if is_or == truthy {
return Ok(result);
}
last_result = Some(result);
}
Ok(if let Some(last_result) = last_result {
last_result
} else {
// there were zero arguments
(!is_or).into()
})
}
// function call or macro expand
_ => {
let mut func_or_macro =
eval_inner(env.clone(), &list.car()?, context.found_tail(true))?;
if matches!(func_or_macro, Value::Macro(_)) {
let args = list.into_iter().skip(1).collect::<Vec<Value>>();
let expanded =
call_function_or_macro(env.clone(), &mut func_or_macro, args)?;
eval_inner(env.clone(), &expanded, Context::new())
} else {
let args = list
.into_iter()
.skip(1)
.map(|car| eval_inner(env.clone(), &car, context.found_tail(true)))
.collect::<Result<Vec<Value>, RuntimeError>>()?;
if !context.found_tail && context.in_func {
Ok(Value::TailCall {
func: Rc::new(func_or_macro),
args,
})
} else {
let mut res =
call_function_or_macro(env.clone(), &mut func_or_macro, args);
while let Ok(Value::TailCall { func, args }) = res {
res = call_function_or_macro(env.clone(), func.as_ref(), args);
}
res
}
}
}
}
}
// plain value
_ => Ok(expression.clone()),
}
}sourcepub fn define(&mut self, key: Symbol, value: Value)
pub fn define(&mut self, key: Symbol, value: Value)
Define a new key in the current environment
Examples found in repository?
src/interpreter.rs (line 107)
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fn eval_inner(
env: Rc<RefCell<Env>>,
expression: &Value,
context: Context,
) -> Result<Value, RuntimeError> {
if context.quoting {
match expression {
Value::List(list) if *list != List::NIL => match &list.car()? {
Value::Symbol(Symbol(keyword)) if keyword == "comma" => {
// do nothing, handle it down below
}
_ => {
return list
.into_iter()
.map(|el| eval_inner(env.clone(), &el, context))
.collect::<Result<List, RuntimeError>>()
.map(Value::List);
}
},
_ => return Ok(expression.clone()),
}
}
match expression {
// look up symbol
Value::Symbol(symbol) => env.borrow().get(symbol).ok_or_else(|| RuntimeError {
msg: format!("\"{}\" is not defined", symbol),
}),
// s-expression
Value::List(list) if *list != List::NIL => {
match &list.car()? {
// special forms
Value::Symbol(Symbol(keyword)) if keyword == "comma" => {
eval_inner(env, &list.cdr().car()?, context.quoting(false))
}
Value::Symbol(Symbol(keyword)) if keyword == "quote" => {
eval_inner(env, &list.cdr().car()?, context.quoting(true))
}
Value::Symbol(Symbol(keyword)) if keyword == "define" || keyword == "set" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let value_expr = require_arg(keyword, args, 1)?;
let value = eval_inner(env.clone(), value_expr, context.found_tail(true))?;
if keyword == "define" {
env.borrow_mut().define(symbol.clone(), value.clone());
} else {
env.borrow_mut().set(symbol.clone(), value.clone())?;
}
Ok(value)
}
Value::Symbol(Symbol(keyword)) if keyword == "defmacro" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let argnames_list = require_typed_arg::<&List>(keyword, args, 1)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr().cdr()));
let lambda = Value::Macro(Lambda {
closure: env.clone(),
argnames,
body,
});
env.borrow_mut().define(symbol.clone(), lambda);
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "defun" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let argnames_list = require_typed_arg::<&List>(keyword, args, 1)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr().cdr()));
let lambda = Value::Lambda(Lambda {
closure: env.clone(),
argnames,
body,
});
env.borrow_mut().define(symbol.clone(), lambda);
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "lambda" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let argnames_list = require_typed_arg::<&List>(keyword, args, 0)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr()));
Ok(Value::Lambda(Lambda {
closure: env,
argnames,
body,
}))
}
Value::Symbol(Symbol(keyword)) if keyword == "let" => {
let let_env = Rc::new(RefCell::new(Env::extend(env)));
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let declarations = require_typed_arg::<&List>(keyword, args, 0)?;
for decl in declarations.into_iter() {
let decl = &decl;
let decl_cons: &List = decl.try_into().map_err(|_| RuntimeError {
msg: format!("Expected declaration clause, found {}", decl),
})?;
let symbol = &decl_cons.car()?;
let symbol: &Symbol = symbol.try_into().map_err(|_| RuntimeError {
msg: format!("Expected symbol for let declaration, found {}", symbol),
})?;
let expr = &decl_cons.cdr().car()?;
let result = eval_inner(let_env.clone(), expr, context.found_tail(true))?;
let_env.borrow_mut().define(symbol.clone(), result);
}
let body = &Value::List(list.cdr().cdr());
let body: &List = body.try_into().map_err(|_| RuntimeError {
msg: format!(
"Expected expression(s) after let-declarations, found {}",
body
),
})?;
eval_block_inner(let_env, body.into_iter(), context)
}
Value::Symbol(Symbol(keyword)) if keyword == "begin" => {
eval_block_inner(env, list.cdr().into_iter(), context)
}
Value::Symbol(Symbol(keyword)) if keyword == "cond" => {
let clauses = list.cdr();
for clause in clauses.into_iter() {
let clause = &clause;
let clause: &List = clause.try_into().map_err(|_| RuntimeError {
msg: format!("Expected conditional clause, found {}", clause),
})?;
let condition = &clause.car()?;
let then = &clause.cdr().car()?;
if eval_inner(env.clone(), condition, context.found_tail(true))?.into() {
return eval_inner(env, then, context);
}
}
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "if" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let condition = require_arg(keyword, args, 0)?;
let then_expr = require_arg(keyword, args, 1)?;
let else_expr = require_arg(keyword, args, 2).ok();
if eval_inner(env.clone(), condition, context.found_tail(true))?.into() {
eval_inner(env, then_expr, context)
} else {
else_expr
.map(|expr| eval_inner(env, &expr, context))
.unwrap_or(Ok(Value::NIL))
}
}
Value::Symbol(Symbol(keyword)) if keyword == "and" || keyword == "or" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let is_or = keyword.as_str() == "or";
let mut last_result: Option<Value> = None;
for arg in args {
let result = eval_inner(env.clone(), arg, context.found_tail(true))?;
let truthy: bool = (&result).into();
if is_or == truthy {
return Ok(result);
}
last_result = Some(result);
}
Ok(if let Some(last_result) = last_result {
last_result
} else {
// there were zero arguments
(!is_or).into()
})
}
// function call or macro expand
_ => {
let mut func_or_macro =
eval_inner(env.clone(), &list.car()?, context.found_tail(true))?;
if matches!(func_or_macro, Value::Macro(_)) {
let args = list.into_iter().skip(1).collect::<Vec<Value>>();
let expanded =
call_function_or_macro(env.clone(), &mut func_or_macro, args)?;
eval_inner(env.clone(), &expanded, Context::new())
} else {
let args = list
.into_iter()
.skip(1)
.map(|car| eval_inner(env.clone(), &car, context.found_tail(true)))
.collect::<Result<Vec<Value>, RuntimeError>>()?;
if !context.found_tail && context.in_func {
Ok(Value::TailCall {
func: Rc::new(func_or_macro),
args,
})
} else {
let mut res =
call_function_or_macro(env.clone(), &mut func_or_macro, args);
while let Ok(Value::TailCall { func, args }) = res {
res = call_function_or_macro(env.clone(), func.as_ref(), args);
}
res
}
}
}
}
}
// plain value
_ => Ok(expression.clone()),
}
}
// 🦀 Boo! Did I scare ya? Haha!
fn value_to_argnames(argnames: List) -> Result<Vec<Symbol>, RuntimeError> {
argnames
.into_iter()
.enumerate()
.map(|(index, arg)| match arg {
Value::Symbol(s) => Ok(s),
_ => Err(RuntimeError {
msg: format!(
"Expected list of arg names, but arg {} is a {}",
index,
arg.type_name()
),
}),
})
.collect()
}
/// Calling a function is separated from the main `eval_inner()` function
/// so that tail calls can be evaluated without just returning themselves
/// as-is as a tail-call.
fn call_function_or_macro(
env: Rc<RefCell<Env>>,
func: &Value,
args: Vec<Value>,
) -> Result<Value, RuntimeError> {
if let Value::NativeFunc(func) = func {
func(env, args)
} else if let Value::NativeClosure(closure) = func {
closure.borrow_mut()(env, args)
} else {
let lambda = match func {
Value::Lambda(lamb) => Some(lamb),
Value::Macro(lamb) => Some(lamb),
_ => None,
};
if let Some(lambda) = lambda {
// bind args
let mut arg_env = Env::extend(lambda.closure.clone());
for (index, arg_name) in lambda.argnames.iter().enumerate() {
if arg_name.0 == "..." {
// rest parameters
arg_env.define(
Symbol::from("..."),
Value::List(args.into_iter().skip(index).collect()),
);
break;
} else {
arg_env.define(arg_name.clone(), args[index].clone());
}
}
// evaluate each line of body
let clauses: &List = lambda.body.as_ref().try_into()?;
eval_block_inner(
Rc::new(RefCell::new(arg_env)),
clauses.into_iter(),
Context {
found_tail: false,
in_func: true,
quoting: false,
},
)
} else {
Err(RuntimeError {
msg: format!("{} is not callable", func),
})
}
}
}More examples
src/default_environment.rs (lines 21-29)
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pub fn default_env() -> Env {
let mut env = Env::new();
env.define(
Symbol::from("print"),
Value::NativeFunc(|_env, args| {
let expr = require_arg("print", &args, 0)?;
println!("{}", &expr);
Ok(expr.clone())
}),
);
env.define(
Symbol::from("is_null"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_null", &args, 0)?;
Ok(Value::from(*val == Value::NIL))
}),
);
env.define(
Symbol::from("is_number"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_number", &args, 0)?;
Ok(match val {
Value::Int(_) => Value::True,
Value::Float(_) => Value::True,
_ => Value::NIL,
})
}),
);
env.define(
Symbol::from("is_symbol"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_symbol", &args, 0)?;
Ok(match val {
Value::Symbol(_) => Value::True,
_ => Value::NIL,
})
}),
);
env.define(
Symbol::from("is_boolean"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_boolean", &args, 0)?;
Ok(match val {
Value::True => Value::True,
Value::False => Value::True,
_ => Value::NIL,
})
}),
);
env.define(
Symbol::from("is_procedure"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_procedure", &args, 0)?;
Ok(match val {
Value::Lambda(_) => Value::True,
Value::NativeFunc(_) => Value::True,
_ => Value::NIL,
})
}),
);
env.define(
Symbol::from("is_pair"),
Value::NativeFunc(|_env, args| {
let val = require_arg("is_pair", &args, 0)?;
Ok(match val {
Value::List(_) => Value::True,
_ => Value::NIL,
})
}),
);
env.define(
Symbol::from("car"),
Value::NativeFunc(|_env, args| {
let list = require_typed_arg::<&List>("car", &args, 0)?;
list.car()
}),
);
env.define(
Symbol::from("cdr"),
Value::NativeFunc(|_env, args| {
let list = require_typed_arg::<&List>("cdr", &args, 0)?;
Ok(Value::List(list.cdr()))
}),
);
env.define(
Symbol::from("cons"),
Value::NativeFunc(|_env, args| {
let car = require_arg("cons", &args, 0)?;
let cdr = require_typed_arg::<&List>("cons", &args, 1)?;
Ok(Value::List(cdr.cons(car.clone())))
}),
);
env.define(
Symbol::from("list"),
Value::NativeFunc(|_env, args| Ok(Value::List(args.iter().collect::<List>()))),
);
env.define(
Symbol::from("nth"),
Value::NativeFunc(|_env, args| {
let index = require_typed_arg::<IntType>("nth", &args, 0)?;
let list = require_typed_arg::<&List>("nth", &args, 1)?;
let index = TryInto::<usize>::try_into(index).map_err(|_| RuntimeError {
msg: "Failed converting to `usize`".to_owned(),
})?;
Ok(list.into_iter().nth(index).unwrap_or(Value::NIL))
}),
);
env.define(
Symbol::from("sort"),
Value::NativeFunc(|_env, args| {
let list = require_typed_arg::<&List>("sort", &args, 0)?;
let mut v: Vec<Value> = list.into_iter().collect();
v.sort();
Ok(Value::List(v.into_iter().collect()))
}),
);
env.define(
Symbol::from("reverse"),
Value::NativeFunc(|_env, args| {
let list = require_typed_arg::<&List>("reverse", &args, 0)?;
let mut v: Vec<Value> = list.into_iter().collect();
v.reverse();
Ok(Value::List(v.into_iter().collect()))
}),
);
env.define(
Symbol::from("map"),
Value::NativeFunc(|env, args| {
let func = require_arg("map", &args, 0)?;
let list = require_typed_arg::<&List>("map", &args, 1)?;
list.into_iter()
.map(|val| {
let expr = lisp! { ({func.clone()} (quote {val})) };
eval(env.clone(), &expr)
})
.collect::<Result<List, RuntimeError>>()
.map(Value::List)
}),
);
// 🦀 Oh the poor `filter`, you must feel really sad being unused.
env.define(
Symbol::from("filter"),
Value::NativeFunc(|env, args| {
let func = require_arg("filter", &args, 0)?;
let list = require_typed_arg::<&List>("filter", &args, 1)?;
list.into_iter()
.filter_map(|val: Value| -> Option<Result<Value, RuntimeError>> {
let expr = lisp! { ({func.clone()} (quote {val.clone()})) };
match eval(env.clone(), &expr) {
Ok(matches) => {
if matches.into() {
Some(Ok(val))
} else {
None
}
}
Err(e) => Some(Err(e)),
}
})
.collect::<Result<List, RuntimeError>>()
.map(Value::List)
}),
);
env.define(
Symbol::from("length"),
Value::NativeFunc(|_env, args| {
let list = require_typed_arg::<&List>("length", &args, 0)?;
cfg_if! {
if #[cfg(feature = "bigint")] {
Ok(Value::Int(list.into_iter().len().into()))
} else {
Ok(Value::Int(list.into_iter().len() as IntType))
}
}
}),
);
env.define(
Symbol::from("range"),
Value::NativeFunc(|_env, args| {
let start = require_typed_arg::<IntType>("range", &args, 0)?;
let end = require_typed_arg::<IntType>("range", &args, 1)?;
let mut current = start;
Ok(Value::List(
std::iter::from_fn(move || {
if current == end {
None
} else {
let res = Some(current.clone());
current += 1;
res
}
})
.map(Value::from)
.collect(),
))
}),
);
env.define(
Symbol::from("hash"),
Value::NativeFunc(|_env, args| {
let chunks = args.chunks(2);
let mut hash = HashMap::new();
for pair in chunks {
let key = pair.get(0).unwrap();
let value = pair.get(1);
if let Some(value) = value {
hash.insert(key.clone(), value.clone());
} else {
return Err(RuntimeError {
msg: format!("Must pass an even number of arguments to 'hash', because they're used as key/value pairs; found extra argument {}", key)
});
}
}
Ok(Value::HashMap(Rc::new(RefCell::new(hash))))
}),
);
env.define(
Symbol::from("hash_get"),
Value::NativeFunc(|_env, args| {
let hash = require_typed_arg::<&HashMapRc>("hash_get", &args, 0)?;
let key = require_arg("hash_get", &args, 1)?;
Ok(hash
.borrow()
.get(key)
.map(|v| v.clone())
.unwrap_or(Value::NIL))
}),
);
env.define(
Symbol::from("hash_set"),
Value::NativeFunc(|_env, args| {
let hash = require_typed_arg::<&HashMapRc>("hash_set", &args, 0)?;
let key = require_arg("hash_set", &args, 1)?;
let value = require_arg("hash_set", &args, 2)?;
hash.borrow_mut().insert(key.clone(), value.clone());
Ok(Value::HashMap(hash.clone()))
}),
);
env.define(
Symbol::from("+"),
Value::NativeFunc(|_env, args| {
let first_arg = require_arg("+", &args, 1)?;
let mut total = match first_arg {
Value::Int(_) => Ok(Value::Int(0.into())),
Value::Float(_) => Ok(Value::Float(0.0)),
Value::String(_) => Ok(Value::String("".into())),
_ => Err(RuntimeError {
msg: format!(
"Function \"+\" requires arguments to be numbers or strings; found {}",
first_arg
),
}),
}?;
for arg in args {
total = (&total + &arg).map_err(|_| RuntimeError {
msg: format!(
"Function \"+\" requires arguments to be numbers or strings; found {}",
arg
),
})?;
}
Ok(total)
}),
);
env.define(
Symbol::from("-"),
Value::NativeFunc(|_env, args| {
let a = require_arg("-", &args, 0)?;
let b = require_arg("-", &args, 1)?;
(a - b).map_err(|_| RuntimeError {
msg: String::from("Function \"-\" requires arguments to be numbers"),
})
}),
);
env.define(
Symbol::from("*"),
Value::NativeFunc(|_env, args| {
let mut product = Value::Int(1.into());
for arg in args {
product = (&product * &arg).map_err(|_| RuntimeError {
msg: format!(
"Function \"*\" requires arguments to be numbers; found {}",
arg
),
})?;
}
Ok(product)
}),
);
env.define(
Symbol::from("/"),
Value::NativeFunc(|_env, args| {
let a = require_arg("/", &args, 0)?;
let b = require_arg("/", &args, 1)?;
(a / b).map_err(|_| RuntimeError {
msg: String::from("Function \"/\" requires arguments to be numbers"),
})
}),
);
env.define(
Symbol::from("truncate"),
Value::NativeFunc(|_env, args| {
let a = require_arg("truncate", &args, 0)?;
let b = require_arg("truncate", &args, 1)?;
if let (Ok(a), Ok(b)) = (
TryInto::<IntType>::try_into(a),
TryInto::<IntType>::try_into(b),
) {
return Ok(Value::Int(a / b));
}
Err(RuntimeError {
msg: String::from("Function \"truncate\" requires arguments to be integers"),
})
}),
);
env.define(
Symbol::from("not"),
Value::NativeFunc(|_env, args| {
let a = require_arg("not", &args, 0)?;
let a: bool = a.into();
Ok(Value::from(!a))
}),
);
env.define(
Symbol::from("=="),
Value::NativeFunc(|_env, args| {
let a = require_arg("==", &args, 0)?;
let b = require_arg("==", &args, 1)?;
Ok(Value::from(a == b))
}),
);
env.define(
Symbol::from("!="),
Value::NativeFunc(|_env, args| {
let a = require_arg("!=", &args, 0)?;
let b = require_arg("!=", &args, 1)?;
Ok(Value::from(a != b))
}),
);
env.define(
Symbol::from("<"),
Value::NativeFunc(|_env, args| {
let a = require_arg("<", &args, 0)?;
let b = require_arg("<", &args, 1)?;
Ok(Value::from(a < b))
}),
);
env.define(
Symbol::from("<="),
Value::NativeFunc(|_env, args| {
let a = require_arg("<=", &args, 0)?;
let b = require_arg("<=", &args, 1)?;
Ok(Value::from(a <= b))
}),
);
env.define(
Symbol::from(">"),
Value::NativeFunc(|_env, args| {
let a = require_arg(">", &args, 0)?;
let b = require_arg(">", &args, 1)?;
Ok(Value::from(a > b))
}),
);
env.define(
Symbol::from(">="),
Value::NativeFunc(|_env, args| {
let a = require_arg(">=", &args, 0)?;
let b = require_arg(">=", &args, 1)?;
Ok(Value::from(a >= b))
}),
);
env.define(
Symbol::from("eval"),
Value::NativeFunc(|env, args| {
let expr = require_arg("eval", &args, 0)?;
eval(env, expr)
}),
);
env.define(
Symbol::from("apply"),
Value::NativeFunc(|env, args| {
let func = require_arg("apply", &args, 0)?;
let params = require_typed_arg::<&List>("apply", &args, 1)?;
eval(env, &Value::List(params.cons(func.clone())))
}),
);
env
}sourcepub fn set(&mut self, key: Symbol, value: Value) -> Result<(), RuntimeError>
pub fn set(&mut self, key: Symbol, value: Value) -> Result<(), RuntimeError>
Find the environment where this key is defined, and update its value. Returns an Err if the symbol has not been defined anywhere in the hierarchy.
Examples found in repository?
src/model/env.rs (line 56)
51 52 53 54 55 56 57 58 59 60 61 62
pub fn set(&mut self, key: Symbol, value: Value) -> Result<(), RuntimeError> {
if self.entries.contains_key(&key) {
self.entries.insert(key, value);
Ok(())
} else if let Some(parent) = &self.parent {
parent.borrow_mut().set(key, value)
} else {
Err(RuntimeError {
msg: format!("Tried to set value of undefined symbol \"{}\"", key),
})
}
}More examples
src/interpreter.rs (line 109)
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fn eval_inner(
env: Rc<RefCell<Env>>,
expression: &Value,
context: Context,
) -> Result<Value, RuntimeError> {
if context.quoting {
match expression {
Value::List(list) if *list != List::NIL => match &list.car()? {
Value::Symbol(Symbol(keyword)) if keyword == "comma" => {
// do nothing, handle it down below
}
_ => {
return list
.into_iter()
.map(|el| eval_inner(env.clone(), &el, context))
.collect::<Result<List, RuntimeError>>()
.map(Value::List);
}
},
_ => return Ok(expression.clone()),
}
}
match expression {
// look up symbol
Value::Symbol(symbol) => env.borrow().get(symbol).ok_or_else(|| RuntimeError {
msg: format!("\"{}\" is not defined", symbol),
}),
// s-expression
Value::List(list) if *list != List::NIL => {
match &list.car()? {
// special forms
Value::Symbol(Symbol(keyword)) if keyword == "comma" => {
eval_inner(env, &list.cdr().car()?, context.quoting(false))
}
Value::Symbol(Symbol(keyword)) if keyword == "quote" => {
eval_inner(env, &list.cdr().car()?, context.quoting(true))
}
Value::Symbol(Symbol(keyword)) if keyword == "define" || keyword == "set" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let value_expr = require_arg(keyword, args, 1)?;
let value = eval_inner(env.clone(), value_expr, context.found_tail(true))?;
if keyword == "define" {
env.borrow_mut().define(symbol.clone(), value.clone());
} else {
env.borrow_mut().set(symbol.clone(), value.clone())?;
}
Ok(value)
}
Value::Symbol(Symbol(keyword)) if keyword == "defmacro" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let argnames_list = require_typed_arg::<&List>(keyword, args, 1)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr().cdr()));
let lambda = Value::Macro(Lambda {
closure: env.clone(),
argnames,
body,
});
env.borrow_mut().define(symbol.clone(), lambda);
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "defun" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let symbol = require_typed_arg::<&Symbol>(keyword, args, 0)?;
let argnames_list = require_typed_arg::<&List>(keyword, args, 1)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr().cdr()));
let lambda = Value::Lambda(Lambda {
closure: env.clone(),
argnames,
body,
});
env.borrow_mut().define(symbol.clone(), lambda);
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "lambda" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let argnames_list = require_typed_arg::<&List>(keyword, args, 0)?;
let argnames = value_to_argnames(argnames_list.clone())?;
let body = Rc::new(Value::List(list.cdr().cdr()));
Ok(Value::Lambda(Lambda {
closure: env,
argnames,
body,
}))
}
Value::Symbol(Symbol(keyword)) if keyword == "let" => {
let let_env = Rc::new(RefCell::new(Env::extend(env)));
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let declarations = require_typed_arg::<&List>(keyword, args, 0)?;
for decl in declarations.into_iter() {
let decl = &decl;
let decl_cons: &List = decl.try_into().map_err(|_| RuntimeError {
msg: format!("Expected declaration clause, found {}", decl),
})?;
let symbol = &decl_cons.car()?;
let symbol: &Symbol = symbol.try_into().map_err(|_| RuntimeError {
msg: format!("Expected symbol for let declaration, found {}", symbol),
})?;
let expr = &decl_cons.cdr().car()?;
let result = eval_inner(let_env.clone(), expr, context.found_tail(true))?;
let_env.borrow_mut().define(symbol.clone(), result);
}
let body = &Value::List(list.cdr().cdr());
let body: &List = body.try_into().map_err(|_| RuntimeError {
msg: format!(
"Expected expression(s) after let-declarations, found {}",
body
),
})?;
eval_block_inner(let_env, body.into_iter(), context)
}
Value::Symbol(Symbol(keyword)) if keyword == "begin" => {
eval_block_inner(env, list.cdr().into_iter(), context)
}
Value::Symbol(Symbol(keyword)) if keyword == "cond" => {
let clauses = list.cdr();
for clause in clauses.into_iter() {
let clause = &clause;
let clause: &List = clause.try_into().map_err(|_| RuntimeError {
msg: format!("Expected conditional clause, found {}", clause),
})?;
let condition = &clause.car()?;
let then = &clause.cdr().car()?;
if eval_inner(env.clone(), condition, context.found_tail(true))?.into() {
return eval_inner(env, then, context);
}
}
Ok(Value::NIL)
}
Value::Symbol(Symbol(keyword)) if keyword == "if" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let condition = require_arg(keyword, args, 0)?;
let then_expr = require_arg(keyword, args, 1)?;
let else_expr = require_arg(keyword, args, 2).ok();
if eval_inner(env.clone(), condition, context.found_tail(true))?.into() {
eval_inner(env, then_expr, context)
} else {
else_expr
.map(|expr| eval_inner(env, &expr, context))
.unwrap_or(Ok(Value::NIL))
}
}
Value::Symbol(Symbol(keyword)) if keyword == "and" || keyword == "or" => {
let args = &list.cdr().into_iter().collect::<Vec<Value>>();
let is_or = keyword.as_str() == "or";
let mut last_result: Option<Value> = None;
for arg in args {
let result = eval_inner(env.clone(), arg, context.found_tail(true))?;
let truthy: bool = (&result).into();
if is_or == truthy {
return Ok(result);
}
last_result = Some(result);
}
Ok(if let Some(last_result) = last_result {
last_result
} else {
// there were zero arguments
(!is_or).into()
})
}
// function call or macro expand
_ => {
let mut func_or_macro =
eval_inner(env.clone(), &list.car()?, context.found_tail(true))?;
if matches!(func_or_macro, Value::Macro(_)) {
let args = list.into_iter().skip(1).collect::<Vec<Value>>();
let expanded =
call_function_or_macro(env.clone(), &mut func_or_macro, args)?;
eval_inner(env.clone(), &expanded, Context::new())
} else {
let args = list
.into_iter()
.skip(1)
.map(|car| eval_inner(env.clone(), &car, context.found_tail(true)))
.collect::<Result<Vec<Value>, RuntimeError>>()?;
if !context.found_tail && context.in_func {
Ok(Value::TailCall {
func: Rc::new(func_or_macro),
args,
})
} else {
let mut res =
call_function_or_macro(env.clone(), &mut func_or_macro, args);
while let Ok(Value::TailCall { func, args }) = res {
res = call_function_or_macro(env.clone(), func.as_ref(), args);
}
res
}
}
}
}
}
// plain value
_ => Ok(expression.clone()),
}
}