[xlii]

Super simple example

    % Prolog
    next_light(green, yellow).
    next_light(yellow, red).
    next_light(red, green).

    % Erlang
    next_light(green)  -> yellow;
    next_light(yellow) -> red;
    next_light(red)    -> green.

Notable differences:

- `;` in Erlang indicates multi clause function

- In Prolog next_light is database, in Erlang it's just a function

Question: What's the light before green?

    % Erlang
    % Returns actual value
    prev_light_search() -> 
    [State || State <- [green, yellow, red], next_light(State) == green].

    % Prolog (?- means that it's in query mode)
    ?- next_light(Light, green).

So syntax IS similar though the thing is that Prolog is more like binding and quering database and Erlang is executing function.

In a nutshell Erlang is more like: "when I have X, then I can calculate Y" and Prolog like "If I want Y, what's the X".