reasonkit-core 0.1.8

//! E-Graph Equality Saturation Engine
//!
//! This module provides integration with egglog for equality saturation
//! and term rewriting. E-graphs allow representing a massive space of
//! equivalent expressions simultaneously.
//!
//! # Use Cases
//! - Code optimization (algebraic simplifications)
//! - Mathematical proof simplification
//! - Query optimization
//! - Program synthesis
//!
//! Enable with: `cargo build --features egraph`

use anyhow::Result;
use serde::{Deserialize, Serialize};

// Re-export egglog for direct access
pub use egglog;

/// Configuration for the E-graph engine
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct EgraphConfig {
    /// Maximum number of iterations for saturation
    pub max_iterations: usize,
    /// Maximum number of nodes in the e-graph
    pub max_nodes: usize,
    /// Enable debug output
    pub debug: bool,
}

impl Default for EgraphConfig {
    fn default() -> Self {
        Self {
            max_iterations: 100,
            max_nodes: 100_000,
            debug: false,
        }
    }
}

/// Rewrite rule for algebraic simplification
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct RewriteRule {
    /// Rule name for debugging
    pub name: String,
    /// Left-hand side pattern
    pub lhs: String,
    /// Right-hand side replacement
    pub rhs: String,
    /// Optional condition for rule application
    pub condition: Option<String>,
}

impl RewriteRule {
    /// Create a new rewrite rule
    pub fn new(name: &str, lhs: &str, rhs: &str) -> Self {
        Self {
            name: name.to_string(),
            lhs: lhs.to_string(),
            rhs: rhs.to_string(),
            condition: None,
        }
    }

    /// Add a condition to the rule
    pub fn with_condition(mut self, condition: &str) -> Self {
        self.condition = Some(condition.to_string());
        self
    }
}

/// Standard algebraic rewrite rules
pub fn algebraic_rules() -> Vec<RewriteRule> {
    vec![
        // Additive identity
        RewriteRule::new("add-zero", "(+ ?x 0)", "?x"),
        RewriteRule::new("add-zero-left", "(+ 0 ?x)", "?x"),
        // Multiplicative identity
        RewriteRule::new("mul-one", "(* ?x 1)", "?x"),
        RewriteRule::new("mul-one-left", "(* 1 ?x)", "?x"),
        // Multiplicative zero
        RewriteRule::new("mul-zero", "(* ?x 0)", "0"),
        RewriteRule::new("mul-zero-left", "(* 0 ?x)", "0"),
        // Commutativity
        RewriteRule::new("add-comm", "(+ ?x ?y)", "(+ ?y ?x)"),
        RewriteRule::new("mul-comm", "(* ?x ?y)", "(* ?y ?x)"),
        // Associativity
        RewriteRule::new("add-assoc", "(+ (+ ?x ?y) ?z)", "(+ ?x (+ ?y ?z))"),
        RewriteRule::new("mul-assoc", "(* (* ?x ?y) ?z)", "(* ?x (* ?y ?z))"),
        // Distributivity
        RewriteRule::new("distribute", "(* ?x (+ ?y ?z))", "(+ (* ?x ?y) (* ?x ?z))"),
        RewriteRule::new("factor", "(+ (* ?x ?y) (* ?x ?z))", "(* ?x (+ ?y ?z))"),
        // Double negation
        RewriteRule::new("double-neg", "(- (- ?x))", "?x"),
        // Self operations
        RewriteRule::new("sub-self", "(- ?x ?x)", "0"),
        RewriteRule::new("div-self", "(/ ?x ?x)", "1").with_condition("(!= ?x 0)"),
    ]
}

/// Boolean logic rewrite rules
pub fn boolean_rules() -> Vec<RewriteRule> {
    vec![
        // Identity
        RewriteRule::new("and-true", "(and ?x true)", "?x"),
        RewriteRule::new("or-false", "(or ?x false)", "?x"),
        // Annihilation
        RewriteRule::new("and-false", "(and ?x false)", "false"),
        RewriteRule::new("or-true", "(or ?x true)", "true"),
        // Idempotence
        RewriteRule::new("and-idem", "(and ?x ?x)", "?x"),
        RewriteRule::new("or-idem", "(or ?x ?x)", "?x"),
        // Double negation
        RewriteRule::new("not-not", "(not (not ?x))", "?x"),
        // De Morgan's laws
        RewriteRule::new(
            "demorgan-and",
            "(not (and ?x ?y))",
            "(or (not ?x) (not ?y))",
        ),
        RewriteRule::new("demorgan-or", "(not (or ?x ?y))", "(and (not ?x) (not ?y))"),
        // Absorption
        RewriteRule::new("absorb-and", "(and ?x (or ?x ?y))", "?x"),
        RewriteRule::new("absorb-or", "(or ?x (and ?x ?y))", "?x"),
    ]
}

/// Expression optimizer using e-graphs
pub struct ExpressionOptimizer {
    config: EgraphConfig,
    rules: Vec<RewriteRule>,
}

impl ExpressionOptimizer {
    /// Create a new optimizer with default algebraic rules
    pub fn new(config: EgraphConfig) -> Self {
        Self {
            config,
            rules: algebraic_rules(),
        }
    }

    /// Create an optimizer with boolean rules
    pub fn boolean(config: EgraphConfig) -> Self {
        Self {
            config,
            rules: boolean_rules(),
        }
    }

    /// Add custom rewrite rules
    pub fn with_rules(mut self, rules: Vec<RewriteRule>) -> Self {
        self.rules.extend(rules);
        self
    }

    /// Get the configuration
    pub fn config(&self) -> &EgraphConfig {
        &self.config
    }

    /// Get the rules
    pub fn rules(&self) -> &[RewriteRule] {
        &self.rules
    }

    /// Optimize an expression (placeholder - actual implementation uses egglog)
    pub fn optimize(&self, expr: &str) -> Result<String> {
        // In production, this would:
        // 1. Parse the expression into egglog format
        // 2. Add all rewrite rules
        // 3. Run equality saturation
        // 4. Extract the smallest equivalent expression

        tracing::debug!(
            expr = expr,
            rules = self.rules.len(),
            max_iterations = self.config.max_iterations,
            "Optimizing expression"
        );

        // For now, return the original expression
        // Full implementation would use egglog::EGraph
        Ok(expr.to_string())
    }
}

impl Default for ExpressionOptimizer {
    fn default() -> Self {
        Self::new(EgraphConfig::default())
    }
}

/// Code optimization agent using e-graphs
///
/// Optimizes generated code by applying rewrite rules
pub struct CodeOptimizer {
    optimizer: ExpressionOptimizer,
}

impl CodeOptimizer {
    /// Create a new code optimizer
    pub fn new() -> Self {
        Self {
            optimizer: ExpressionOptimizer::new(EgraphConfig::default()),
        }
    }

    /// Optimize a code expression
    pub fn optimize_expr(&self, code: &str) -> Result<String> {
        self.optimizer.optimize(code)
    }
}

impl Default for CodeOptimizer {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_config_default() {
        let config = EgraphConfig::default();
        assert_eq!(config.max_iterations, 100);
        assert!(!config.debug);
    }

    #[test]
    fn test_rewrite_rule() {
        let rule = RewriteRule::new("test", "(+ ?x 0)", "?x");
        assert_eq!(rule.name, "test");
        assert!(rule.condition.is_none());
    }

    #[test]
    fn test_algebraic_rules() {
        let rules = algebraic_rules();
        assert!(!rules.is_empty());
        assert!(rules.iter().any(|r| r.name == "add-zero"));
    }

    #[test]
    fn test_optimizer() {
        let optimizer = ExpressionOptimizer::default();
        let result = optimizer.optimize("(+ x 0)").unwrap();
        assert!(!result.is_empty());
    }
}