In his 1974 foundational book on automata theory, Samuel Eilenberg defined an interesting generalization of finite-state automata, which he called "X-machines". This theory is not well known. It turns out that this notion, appropriately made constructive, gives a very interesting foundation for relational programming. This was investigated by Benoit Razet, in his 2009 thesis "Machines d'Eilenberg effectives". Razet gave a general framework generalizing Gerard Huet's Zen functional programming toolkit for computational linguistics, which was successfully applied to a platform of computational treatment of the Sanskrit language. The talk will explain the main notions of effective Eilenberg machines, and will demonstrate their use in various tasks of computational linguistics.