92 lines
2.3 KiB
Rust
92 lines
2.3 KiB
Rust
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//! Atoms represent predicates applied to terms.
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use std::fmt;
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use super::term::Term;
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/// An atom is a predicate symbol applied to a tuple of terms.
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/// Example: Parent(alice, bob) or Ancestor(?X, ?Y)
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#[derive(Debug, Clone, PartialEq, Eq, Hash)]
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pub struct Atom {
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/// The predicate name.
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pub predicate: String,
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/// The arguments to the predicate.
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pub terms: Vec<Term>,
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}
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impl Atom {
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/// Create a new atom with the given predicate and terms.
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pub fn new(predicate: impl Into<String>, terms: Vec<Term>) -> Self {
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Atom {
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predicate: predicate.into(),
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terms,
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}
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}
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/// Returns the arity (number of arguments) of this atom.
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pub fn arity(&self) -> usize {
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self.terms.len()
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}
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/// Returns true if this atom is ground (contains no variables).
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pub fn is_ground(&self) -> bool {
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self.terms.iter().all(|t| t.is_ground())
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}
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/// Get all variables in this atom.
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pub fn variables(&self) -> Vec<&String> {
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self.terms
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.iter()
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.filter_map(|t| match t {
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Term::Variable(v) => Some(v),
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_ => None,
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})
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.collect()
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}
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}
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impl fmt::Display for Atom {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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write!(f, "{}(", self.predicate)?;
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for (i, term) in self.terms.iter().enumerate() {
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if i > 0 {
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write!(f, ", ")?;
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}
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write!(f, "{}", term)?;
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}
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write!(f, ")")
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_atom_creation() {
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let atom = Atom::new(
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"Parent",
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vec![Term::constant("alice"), Term::constant("bob")],
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);
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assert_eq!(atom.predicate, "Parent");
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assert_eq!(atom.arity(), 2);
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assert!(atom.is_ground());
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}
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#[test]
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fn test_atom_with_variables() {
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let atom = Atom::new("Ancestor", vec![Term::var("X"), Term::var("Y")]);
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assert!(!atom.is_ground());
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assert_eq!(atom.variables().len(), 2);
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}
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#[test]
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fn test_atom_display() {
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let atom = Atom::new(
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"Parent",
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vec![Term::constant("alice"), Term::constant("bob")],
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);
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assert_eq!(format!("{}", atom), "Parent(alice, bob)");
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}
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}
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