Finite state machine: Difference between revisions

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=={{header|Prolog}}==

<lang Prolog>state(ready, deposit, waiting).

state(ready, quit, exit).

state(waiting, select, dispense).

state(waiting, refund, refunding).

state(dispense, remove, ready).

message(ready, 'Please deposit coins.~n').

message(waiting, 'Please select an item, or refund coins.~n').

message(dispense, 'Please remove your item.~n').

message(refunding, 'Coins have been refunded~n').

act :- act(ready).

act(exit).

act(refunding) :-

print_message(refunding),

act(ready).

act(State) :-

dif(State, exit),

print_message(State),

read(Action),

state(State, Action, NextState),

act(NextState).

print_message(State) :- message(State, Message), format(Message).</lang>

{{out}}

<pre>

2 ?- act.

Please deposit coins.

|: deposit.

Please select an item, or refund coins.

|: select.

Please remove your item.

|: remove.

Please deposit coins.

|: deposit.

Please select an item, or refund coins.

|: refund.

Coins have been refunded

Please deposit coins.

|: quit.

true .