Hello, As an exercice to learn monadic programming, I programmed a Non-Deterministic State Machine. I extended the exercice to include the deterministic "cut" function, exactly as the one existing in Prolog. That means I defined an evalutaion frame, and if the machine evaluates a "cut", that means no other alternatives are to be evaluated in the inner-most frame. In Prolog, each predicates defines also a frame. To further extend my experiment, I wanted to implement my State Machine as a Monad Transformer. But there, even if it's working, I cannot anymore work with infinite choice points :( So I was looking for some existing implementation, to try understand what I did and even if it is possible. Thanks, Pierre -- Pierre Barbier de Reuille INRA - UMR Cirad/Inra/Cnrs/Univ.MontpellierII AMAP Botanique et Bio-informatique de l'Architecture des Plantes TA40/PSII, Boulevard de la Lironde 34398 MONTPELLIER CEDEX 5, France tel : (33) 4 67 61 65 77 fax : (33) 4 67 61 56 68