merc_sabre 1.0.0

Implements a term rewrite engine based on a set automaton based rewriter.
Documentation 
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#![forbid(unsafe_code)]

use std::fmt;

use itertools::Itertools;
use merc_data::DataExpression;

/// A rewrite specification is a set of rewrite rules, given by [Rule].
#[derive(Debug, Default, Clone)]
pub struct RewriteSpecification {
    rewrite_rules: Vec<Rule>,
}

impl RewriteSpecification {
    /// Create a new, empty rewrite specification.
    pub fn new(rewrite_rules: Vec<Rule>) -> RewriteSpecification {
        RewriteSpecification {
            rewrite_rules,
        }
    }

    /// Returns the rewrite rules of this specification.
    pub fn rewrite_rules(&self) -> &[Rule] {
        &self.rewrite_rules
    }   
}

/// A condition of a conditional rewrite rule.
/// 
/// Either `lhs == rhs` or `lhs != rhs` depending on equality being true.
#[derive(Clone, Debug, Eq, Hash, PartialEq, Ord, PartialOrd)]
pub struct Condition {
    pub lhs: DataExpression,
    pub rhs: DataExpression,
    pub equality: bool,
}

/// A rewrite rule.
#[derive(Debug, Clone, Eq, PartialEq, Hash, Ord, PartialOrd)]
pub struct Rule {
    /// A conjunction of clauses
    pub conditions: Vec<Condition>,
    pub lhs: DataExpression,
    pub rhs: DataExpression,
}

impl fmt::Display for RewriteSpecification {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        for rule in &self.rewrite_rules {
            writeln!(f, "{rule}")?;
        }
        Ok(())
    }
}

impl fmt::Display for Rule {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if self.conditions.is_empty() {
            write!(f, "{} = {}", self.lhs, self.rhs)
        } else {
            write!(
                f,
                "{} -> {} = {}",
                self.conditions.iter().format(", "),
                self.lhs,
                self.rhs
            )
        }
    }
}

impl fmt::Display for Condition {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if self.equality {
            write!(f, "{} == {}", self.lhs, self.rhs)
        } else {
            write!(f, "{} <> {}", self.lhs, self.rhs)
        }
    }
}