scryer-prolog 0.8.51

A modern Prolog implementation written mostly in Rust.
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use std::cell::Cell;

use l1::ast::{Atom, Reg, Term, TopLevel, Var};

grammar;

pub TopLevel: TopLevel = {
    "?-" <t:Term> "." => TopLevel::Query(t),
    <t:Term> "."      => TopLevel::Fact(t),
};

Atom : Atom = {
    r"[a-z][a-z0-9_]*" => <>.trim().to_string(),
};

Var : Var = {
    r"[A-Z][a-z0-9_]*" => <>.trim().to_string(),
};

BoxedTerm : Box<Term> = {
    <t:Term> => Box::new(t),
};

Term : Term = {
    <a:Atom> "(" <ts: (<BoxedTerm> ",")*> <t:BoxedTerm> ")" => {
     	let mut ts = ts;
     	ts.push(t);
	Term::Clause(Cell::new(0), a, ts)
    },
    <Atom> => Term::Atom(Cell::new(0), <>),
    <Var>  => Term::Var(Cell::new(Reg::Norm(0)), <>)
};