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//!
//! A list of terms, where T is the type of the elements in the list.
#![forbid(unsafe_code)]
use std::fmt;
use std::marker::PhantomData;
use delegate::delegate;
use itertools::Itertools;
use merc_utilities::MercError;
use crate::ATerm;
use crate::ATermArgs;
use crate::ATermIndex;
use crate::ATermRef;
use crate::SymbolRef;
use crate::Term;
use crate::TermIterator;
use crate::storage::THREAD_TERM_POOL;
/// Returns true iff the term is a list term.
pub fn is_list_term<'a, 'b>(t: &'b impl Term<'a, 'b>) -> bool {
THREAD_TERM_POOL.with_borrow(|tp| *tp.list_symbol() == t.get_head_symbol())
}
/// Returns true iff the term is an empty list.
pub fn is_empty_list_term<'a, 'b>(t: &'b impl Term<'a, 'b>) -> bool {
THREAD_TERM_POOL.with_borrow(|tp| *tp.empty_list_symbol() == t.get_head_symbol())
/// Represents a list of ATerms of type T.
///
/// # Details
/// Internally, uses two standard function symbols `cons` and `[]` to represent
/// lists. The `cons` function symbol has arity 2, where the first argument is
/// the head of the list and the second argument is the tail of the list. The
/// `[]` function symbol has arity 0 and represents the empty list.
pub struct ATermList<T> {
term: ATerm,
_marker: PhantomData<T>,
// TODO: This should use the trait Term<'a, 'b>
impl<T: From<ATerm>> ATermList<T> {
/// Obtain the head, i.e. the first element, of the list.
pub fn head(&self) -> T {
self.term.arg(0).protect().into()
/// Converts the list into a vector.
pub fn to_vec(&self) -> Vec<T> {
self.iter().collect()
impl<T> ATermList<T> {
/// Constructs a new list from an iterator that is consumed.
pub fn from_double_iter(iter: impl DoubleEndedIterator<Item = T>) -> Self
where
T: Into<ATerm>,
{
let mut list = Self::empty();
for item in iter.rev() {
list = list.cons(item);
list
pub fn try_from_double_iter(iter: impl DoubleEndedIterator<Item = Result<T, MercError>>) -> Result<Self, MercError>
list = list.cons(item?);
Ok(list)
/// Constructs a new list with the given item as the head and the current list as the tail.
pub fn cons(&self, item: T) -> Self
ATermList {
term: THREAD_TERM_POOL.with_borrow(|tp| {
ATerm::with_args(tp.list_symbol(), &[item.into().copy(), self.term.copy()]).protect()
}),
_marker: PhantomData,
/// Constructs the empty list.
pub fn empty() -> Self {
term: THREAD_TERM_POOL.with_borrow(|tp| ATerm::constant(tp.empty_list_symbol())),
/// Returns true iff the list is empty.
pub fn is_empty(&self) -> bool {
is_empty_list_term(&self.term)
/// Obtain the tail, i.e. the remainder, of the list.
pub fn tail(&self) -> ATermList<T> {
self.term.arg(1).into()
/// Returns an iterator over all elements in the list.
pub fn iter(&self) -> ATermListIter<T> {
ATermListIter { current: self.clone() }
impl<'a, 'b, T> Term<'a, 'b> for ATermList<T>
'b: 'a,
delegate! {
to self.term {
fn protect(&self) -> ATerm;
fn arg(&'b self, index: usize) -> ATermRef<'a>;
fn arguments(&'b self) -> ATermArgs<'a>;
fn copy(&'b self) -> ATermRef<'a>;
fn get_head_symbol(&'b self) -> SymbolRef<'a>;
fn iter(&'b self) -> TermIterator<'a>;
fn index(&self) -> usize;
fn shared(&self) -> &ATermIndex;
fn annotation(&self) -> Option<usize>;
impl<T> Clone for ATermList<T> {
fn clone(&self) -> Self {
term: self.term.clone(),
impl<T> From<ATermList<T>> for ATerm {
fn from(value: ATermList<T>) -> Self {
value.term
impl<T: From<ATerm>> Iterator for ATermListIter<T> {
type Item = T;
fn next(&mut self) -> Option<Self::Item> {
if self.current.is_empty() {
None
} else {
let head = self.current.head();
self.current = self.current.tail();
Some(head)
impl<T> From<ATerm> for ATermList<T> {
fn from(value: ATerm) -> Self {
debug_assert!(
is_list_term(&value) || is_empty_list_term(&value),
"Can only convert an aterm_list"
);
ATermList::<T> {
term: value,
impl<'a, T> From<ATermRef<'a>> for ATermList<T> {
fn from(value: ATermRef<'a>) -> Self {
term: value.protect(),
impl<T: From<ATerm>> IntoIterator for ATermList<T> {
type IntoIter = ATermListIter<T>;
fn into_iter(self) -> Self::IntoIter {
self.iter()
impl<T: From<ATerm>> IntoIterator for &ATermList<T> {
impl<T: From<ATerm> + fmt::Display> fmt::Display for ATermList<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "[{}]", self.iter().format(","))
/// The iterator over the elements of an [ATermList].
pub struct ATermListIter<T> {
current: ATermList<T>,
#[cfg(test)]
mod tests {
#[test]
fn test_list_term() {
use super::*;
use crate::ATermInt;
let list = ATermList::from_double_iter(vec![ATermInt::new(1), ATermInt::new(2), ATermInt::new(3)].into_iter());
assert_eq!(list.head().value(), 1);
assert_eq!(list.tail().head().value(), 2);
assert_eq!(list.tail().tail().head().value(), 3);
assert!(list.tail().tail().tail().is_empty());