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//! Generic normalising rules for associative-commutative operators.
use std::collections::VecDeque;
use std::mem::Discriminant;
use conjure_cp::ast::{Expression as Expr, SymbolTable};
use conjure_cp::rule_engine::{
ApplicationError::RuleNotApplicable, ApplicationResult, Reduction, register_rule,
};
use uniplate::Biplate;
/// Normalises associative_commutative operations.
///
/// For now, this just removes nested expressions by associativity.
/// ```text
/// v(v(a,b,...),c,d,...) ~> v(a,b,c,d)
/// where v is an AC vector operator
/// ```
#[register_rule(("Base", 8900))]
fn normalise_associative_commutative(expr: &Expr, _: &SymbolTable) -> ApplicationResult {
if !expr.is_associative_commutative_operator() {
return Err(RuleNotApplicable);
}
// remove nesting deeply
fn recurse_deeply(
root_discriminant: Discriminant<Expr>,
expr: Expr,
changed: &mut bool,
) -> Vec<Expr> {
// if expr a different expression type, stop recursing
if std::mem::discriminant(&expr) != root_discriminant {
return vec![expr];
let child_vecs: VecDeque<Vec<Expr>> = expr.children_bi();
// empty expression
if child_vecs.is_empty() {
// go deeper
let children = child_vecs[0].clone();
let old_len = children.len();
let new_children = children
.into_iter()
.flat_map(|child| recurse_deeply(root_discriminant, child, changed))
.collect::<Vec<_>>();
if new_children.len() != old_len {
*changed = true;
new_children
let mut changed = false;
let new_children = recurse_deeply(std::mem::discriminant(expr), expr.clone(), &mut changed);
if !changed {
let new_expr = expr.with_children_bi(vec![new_children].into());
Ok(Reduction::pure(new_expr))