package prolog.builtins

import prolog.components.terms.Atom
import prolog.components.terms.Structure
import prolog.components.terms.Term
import prolog.components.terms.Variable

/**
 * True if Term1 is equivalent to Term2. A variable is only identical to a sharing variable.
 */
fun equivalent(term1: Term, term2: Term): Boolean {
    return when {
        term1 is Variable && term2 is Variable -> term1 == term2
        term1 is Variable -> term1.alias().isPresent && equivalent(term1.alias().get(), term2)
        term2 is Variable -> term2.alias().isPresent && equivalent(term2.alias().get(), term1)
        term1 is Atom && term2 is Atom -> term1.compareTo(term2) == 0
        term1 is Structure && term2 is Structure -> term1.compareTo(term2) == 0
        else -> false
    }
}