private IEnumerable <Context> UnifySequences([NotNull] PairVar left, [NotNull] PairVar right)
{
if (left.IsEmpty || right.IsEmpty)
{
return(left.IsEmpty && right.IsEmpty ? Just(this) : Nothing);
}
return(Unify(left.Head(), right.Head())
.SelectMany(c => c.Unify(left.Tail(), right.Tail())));
}
private Var ReifyImpl([NotNull] PairVar pair) => pair.IsEmpty ? Kanrenmo.Var.Empty : new PairVar(Reify(pair.Head()), Reify(pair.Tail()));