simple_term_rewriter 0.3.0

/*
Copyright 2024 Erwan Mahe (github.com/erwanM974)

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/


use crate::builtin_trs::util::{fold_associative_sub_terms_recursively, get_associative_sub_terms_recursively, is_greater_as_per_lexicographic_path_ordering};
use crate::core::terms::position::PositionInLanguageTerm;
use crate::core::terms::term::{LanguageTerm, RewritableLanguageOperatorSymbol};



 pub trait ModuloAssociativePartialReorderer<LOS : RewritableLanguageOperatorSymbol> {

    fn is_an_associative_partially_commutative_binary_operator_we_may_consider(
        &self, 
        op : &LOS
    ) -> bool;

    fn may_commute_under(
        &self,
        parent_op :&LOS,
        left_sub_term : &LanguageTerm<LOS>,
        right_sub_term : &LanguageTerm<LOS>,
    ) -> bool;

    fn compare_operators(
        &self,
        op1 : &LOS,
        op2 : &LOS
    ) -> std::cmp::Ordering;
    fn get_arity(
        &self,
        op : &LOS
    ) -> usize;

}



fn ad_hoc_partially_commutative_recursive_reorderer<
    LOS : RewritableLanguageOperatorSymbol
>(
    checker : &Box<dyn ModuloAssociativePartialReorderer<LOS>>,
    considered_ac_operator : &LOS,
    flattened_sub_terms : Vec<LanguageTerm<LOS>>,
    has_changed : &mut bool
) -> Vec<LanguageTerm<LOS>> {
    if flattened_sub_terms.len() <= 1 {
        return flattened_sub_terms;
    }

    let mut flattened_sub_terms = flattened_sub_terms;
    // get the head
    let head = flattened_sub_terms.remove(0);
    // then sort the tail
    let mut sorted_tail = ad_hoc_partially_commutative_recursive_reorderer(
        checker, 
        considered_ac_operator,
        flattened_sub_terms,
        has_changed
    );
    // then compare the head with the head of the sorted tail
    let heaf_of_sorted_tail = sorted_tail.remove(0);
    let mut remainder = sorted_tail;
    if checker.may_commute_under(
        considered_ac_operator, 
        &head,
        &heaf_of_sorted_tail
    ) && is_greater_as_per_lexicographic_path_ordering(
        &head, 
        &heaf_of_sorted_tail, 
        &|x,y| checker.compare_operators(x,y),
        &|x| checker.get_arity(x),
    ) {
        // here the "head_of_sorted_tail" should be put before the "head"
        *has_changed = true;
        // ***
        remainder.insert(0, head);
        let mut remainder = ad_hoc_partially_commutative_recursive_reorderer(
            checker, 
            considered_ac_operator,
            remainder,has_changed
        );
        remainder.insert(0, heaf_of_sorted_tail);
        remainder
    } else {
        remainder.insert(0, heaf_of_sorted_tail);
        remainder.insert(0, head);
        remainder
    }
}


pub(crate) fn transformation_modulo_assoc_partial_reordering<
    LOS : RewritableLanguageOperatorSymbol
>(
    checker : &Box<dyn ModuloAssociativePartialReorderer<LOS>>,
    term : &LanguageTerm<LOS>,
    context_term : &LanguageTerm<LOS>,
    position_in_context_term : &PositionInLanguageTerm
) -> Option<LanguageTerm<LOS>> {

    if checker.is_an_associative_partially_commutative_binary_operator_we_may_consider(&term.operator) {
        let considered_ac_operator = &term.operator;

        {
            // if the parent is also the same operator, do not try applyng the transformation
            // as it can be done from the parent
            if let Some(parent_pos) = position_in_context_term.get_parent_position() {
                if let Some(parent_term) = context_term.get_sub_term_at_position(
                    &parent_pos
                ) {
                    if &parent_term.operator == considered_ac_operator {
                        return None;
                    }
                }
            }
        }

        let flattened_sub_terms : Vec<LanguageTerm<LOS>> = get_associative_sub_terms_recursively(
            term, 
            considered_ac_operator
        ).iter().copied().cloned().collect();
        // ***
        let mut has_changed = false;
        let mut sorted_flattened_sub_terms = ad_hoc_partially_commutative_recursive_reorderer(
            checker, 
            considered_ac_operator, 
            flattened_sub_terms, 
            &mut has_changed
        );
        // ***
        if has_changed {
            let folded_transformed = fold_associative_sub_terms_recursively(
                considered_ac_operator,
                &mut sorted_flattened_sub_terms, 
                &None
            );
            return Some(folded_transformed);
        }
    }
    // ***
    None
}



#[cfg(test)]
mod test {
    use crate::{builtin_trs::util::{fold_associative_sub_terms_recursively, get_associative_sub_terms_recursively}, core::terms::{position::PositionInLanguageTerm, term::{LanguageTerm, RewritableLanguageOperatorSymbol}}};

    use super::{transformation_modulo_assoc_partial_reordering, ModuloAssociativePartialReorderer};



    #[derive(Clone, PartialEq, Eq, Hash, Debug)]
    enum TestOperator {
        USIZE(usize),
        STOP,
        THEN
    }

    impl RewritableLanguageOperatorSymbol for TestOperator {}

    struct ReordererChecker {}

    impl ModuloAssociativePartialReorderer<TestOperator> for ReordererChecker {
        fn is_an_associative_partially_commutative_binary_operator_we_may_consider(
            &self, 
            op : &TestOperator
        ) -> bool {
            op == &TestOperator::THEN
        }
    
        fn may_commute_under(
            &self,
            parent_op :&TestOperator,
            left_sub_term : &crate::core::terms::term::LanguageTerm<TestOperator>,
            right_sub_term : &crate::core::terms::term::LanguageTerm<TestOperator>,
        ) -> bool {
            assert!(parent_op == &TestOperator::THEN);
            left_sub_term.operator != TestOperator::STOP && right_sub_term.operator != TestOperator::STOP
        }
    
        fn compare_operators(
            &self,
            op1 : &TestOperator,
            op2 : &TestOperator
        ) -> std::cmp::Ordering {
            match (op1,op2) {
                (TestOperator::USIZE(u1),TestOperator::USIZE(u2)) => {
                    usize::cmp(u1,u2)
                },
                (TestOperator::USIZE(_),_) => {
                    std::cmp::Ordering::Less
                },
                (_,TestOperator::USIZE(_)) => {
                    std::cmp::Ordering::Greater
                },
                (TestOperator::STOP,TestOperator::STOP) => {
                    std::cmp::Ordering::Equal
                },
                (TestOperator::STOP,_) => {
                    std::cmp::Ordering::Less
                },
                (_,TestOperator::STOP) => {
                    std::cmp::Ordering::Greater
                },
                (TestOperator::THEN,TestOperator::THEN) => {
                    std::cmp::Ordering::Equal
                }
            }
        }
    
        fn get_arity(
            &self,
            op : &TestOperator
        ) -> usize {
            match op {
                TestOperator::THEN => {
                    2
                },
                _ => {
                    0
                }
            }
        }
    }

    #[test]
    fn test_reordering() {
        let term = {
            let mut sub_terms : Vec<LanguageTerm<TestOperator>> = vec![
                TestOperator::USIZE(3),
                TestOperator::USIZE(9),
                TestOperator::USIZE(7),
                TestOperator::STOP,
                TestOperator::USIZE(4),
                TestOperator::USIZE(10),
                TestOperator::STOP,
                TestOperator::USIZE(2),
                TestOperator::USIZE(1),
                TestOperator::USIZE(6)
            ].into_iter().map(|x| LanguageTerm::new(x, vec![])).collect();
            fold_associative_sub_terms_recursively(
                &TestOperator::THEN, 
                &mut sub_terms, 
                &None
            )
        };
        let reordered : Box<dyn ModuloAssociativePartialReorderer<TestOperator>> = Box::new(ReordererChecker{});

        let got = transformation_modulo_assoc_partial_reordering(
            &reordered,
            &term,
            &term,
            &PositionInLanguageTerm::get_root_position()
        );
        assert!(got.is_some());
        if let Some(reordered) = got {
            let flattened_reordered : Vec<TestOperator> = get_associative_sub_terms_recursively(
                &reordered, 
                &TestOperator::THEN
            ).into_iter().map(|x| x.operator.clone()).collect();
            assert_eq!(
                flattened_reordered,
                vec![
                    TestOperator::USIZE(3),
                    TestOperator::USIZE(7),
                    TestOperator::USIZE(9),
                    TestOperator::STOP,
                    TestOperator::USIZE(4),
                    TestOperator::USIZE(10),
                    TestOperator::STOP,
                    TestOperator::USIZE(1),
                    TestOperator::USIZE(2),
                    TestOperator::USIZE(6)
                ]
            );
        }
    }

}