80 lines
2.0 KiB
Rust
80 lines
2.0 KiB
Rust
|
//! Terms represent values in the chase: constants or labeled nulls.
|
||
|
|
|
||
|
|
use std::fmt;
|
||
|
|
|
||
|
|
/// A term is either a constant (from the input) or a null (invented during chase).
|
||
|
|
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
|
||
|
|
pub enum Term {
|
||
|
|
/// A constant value from the domain.
|
||
|
|
Constant(String),
|
||
|
|
/// A labeled null (invented value) created during the chase.
|
||
|
|
/// The usize is a unique identifier for this null.
|
||
|
|
Null(usize),
|
||
|
|
/// A variable (used in rule bodies/heads, not in instances).
|
||
|
|
Variable(String),
|
||
|
|
}
|
||
|
|
|
||
|
|
impl Term {
|
||
|
|
/// Create a new constant term.
|
||
|
|
pub fn constant(value: impl Into<String>) -> Self {
|
||
|
|
Term::Constant(value.into())
|
||
|
|
}
|
||
|
|
|
||
|
|
/// Create a new null term with the given id.
|
||
|
|
pub fn null(id: usize) -> Self {
|
||
|
|
Term::Null(id)
|
||
|
|
}
|
||
|
|
|
||
|
|
/// Create a new variable term.
|
||
|
|
pub fn var(name: impl Into<String>) -> Self {
|
||
|
|
Term::Variable(name.into())
|
||
|
|
}
|
||
|
|
|
||
|
|
/// Returns true if this term is a variable.
|
||
|
|
pub fn is_variable(&self) -> bool {
|
||
|
|
matches!(self, Term::Variable(_))
|
||
|
|
}
|
||
|
|
|
||
|
|
/// Returns true if this term is ground (not a variable).
|
||
|
|
pub fn is_ground(&self) -> bool {
|
||
|
|
!self.is_variable()
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
impl fmt::Display for Term {
|
||
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||
|
|
match self {
|
||
|
|
Term::Constant(c) => write!(f, "{}", c),
|
||
|
|
Term::Null(id) => write!(f, "⊥{}", id),
|
||
|
|
Term::Variable(v) => write!(f, "?{}", v),
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
#[cfg(test)]
|
||
|
|
mod tests {
|
||
|
|
use super::*;
|
||
|
|
|
||
|
|
#[test]
|
||
|
|
fn test_term_creation() {
|
||
|
|
let c = Term::constant("alice");
|
||
|
|
let n = Term::null(1);
|
||
|
|
let v = Term::var("X");
|
||
|
|
|
||
|
|
assert!(matches!(c, Term::Constant(_)));
|
||
|
|
assert!(matches!(n, Term::Null(1)));
|
||
|
|
assert!(matches!(v, Term::Variable(_)));
|
||
|
|
}
|
||
|
|
|
||
|
|
#[test]
|
||
|
|
fn test_term_properties() {
|
||
|
|
let c = Term::constant("alice");
|
||
|
|
let v = Term::var("X");
|
||
|
|
|
||
|
|
assert!(c.is_ground());
|
||
|
|
assert!(!c.is_variable());
|
||
|
|
assert!(!v.is_ground());
|
||
|
|
assert!(v.is_variable());
|
||
|
|
}
|
||
|
|
}
|