The maybe monad, hard coded in Prolog, just for fun and IRC play time.

maybe_monad.pl

maybe(just(_)).
maybe(nothing).

bind(nothing, _, nothing).
bind(just(A), P, M) :- call(P, A, M),
                       maybe(M).

return(X, just(X)).

maybe_div(_,0,nothing) :- !.
maybe_div(A,B,just(C)) :- B =\= 0,
                          C is A / B.

/*

?- return("Testing!", X).
X = just("Testing!").

?- return(just("Hi #logic! I'm nested!"), X).
X = just(just("Hi #logic! I'm nested!")).

?- bind(just(20), maybe_div(100), M).
M = just(5).

?- bind(just(0), maybe_div(20), M).
M = nothing.
*/