Trait CostModel

pub trait CostModel<C: Cost> {
    // Required methods
    fn fold(&self, head: &str, children_cost: &[C], head_cost: C) -> C;
    fn enode_cost(
        &self,
        egraph: &EGraph,
        func: &Function,
        row: &FunctionRow<'_>,
    ) -> C;

    // Provided methods
    fn container_cost(
        &self,
        egraph: &EGraph,
        sort: &ArcSort,
        value: Value,
        element_costs: &[C],
    ) -> C { ... }
    fn base_value_cost(
        &self,
        egraph: &EGraph,
        sort: &ArcSort,
        value: Value,
    ) -> C { ... }
}

An interface for custom cost model.

To use it with the default extractor, the cost type must also satisfy Ord + Eq + Clone + Debug. Additionally, the cost model should guarantee that a term has a no-smaller cost than its subterms to avoid cycles in the extracted terms for common case usages. For more niche usages, a term can have a cost less than its subterms. As long as there is no negative cost cycle, the default extractor is guaranteed to terminate in computing the costs. However, the user needs to be careful to guarantee acyclicity in the extracted terms.

Required Methods

fn fold(&self, head: &str, children_cost: &[C], head_cost: C) -> C

The total cost of a term given the cost of the root e-node and its immediate children’s total costs.

fn enode_cost( &self, egraph: &EGraph, func: &Function, row: &FunctionRow<'_>, ) -> C

The cost of an enode (without the cost of children)

Provided Methods

fn container_cost( &self, egraph: &EGraph, sort: &ArcSort, value: Value, element_costs: &[C], ) -> C

The cost of a container value given the costs of its elements.

The default cost for containers is just the sum of all the elements inside

fn base_value_cost(&self, egraph: &EGraph, sort: &ArcSort, value: Value) -> C

Compute the cost of a (non-container) primitive value.

The default cost for base values is the constant one

Implementors

impl CostModel<u64> for TreeAdditiveCostModel