Stair-climbing puzzle: Difference between revisions

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@@ Line 910: / Line 910: @@
 =={{header|Prolog}}==
 The robot code is very short
-<lang Prolog>step_robot :- repeat, step, fail.</lang>
+<lang Prolog>step_up :- \+ step, step_up, step_up.</lang>
-The test program uses a global variable to store the current level and then implements the step behaviour which determines and reports the success of the step and updates the level.
-This is capped at 20 steps but removing the last line will enable the program to run forever.
-<lang Prolog>test_step_robot :-
-	nb_setval(level, 1),
-	step_robot.
+The test program keeps track of the level in a dynamic predicate.
+<lang Prolog>:- dynamic level/1.
+setup :-
+	retractall(level(_)),
+	assert(level(1)).
 step :-
-	nb_getval(level, Level),
+	level(Level),
 	random_between(0,3,N),
 	(
@@ Line 928: / Line 928: @@
 			succ(NewLevel, Level), format('Fell down to ~d~n', NewLevel)
 	),
-	nb_setval(level, NewLevel),
+	retractall(level(Level)),
+	assert(level(NewLevel)),
-	NewLevel >= 20 -> abort.</lang>
+	N > 0. % Fail if 0 because that is a non step up.</lang>
 {{out}}
 <pre>
+?- setup, between(1,10,_), step_up, fail.
-?- test_step_robot.
 Climbed up to 2
 Climbed up to 3
@@ Line 939: / Line 940: @@
 Fell down to 4
 Climbed up to 5
+Climbed up to 6
+Fell down to 5
 Climbed up to 6
 Climbed up to 7
 Climbed up to 8
-Climbed up to 9
+Fell down to 7
-Climbed up to 10
+Climbed up to 8
+false.
-Fell down to 9
-Climbed up to 10
-Climbed up to 11
-Climbed up to 12
-Climbed up to 13
-Climbed up to 14
-Climbed up to 15
-Climbed up to 16
-Climbed up to 17
-Climbed up to 18
-Fell down to 17
-Climbed up to 18
-Climbed up to 19
-Climbed up to 20
-% Execution Aborted
 ?-
 </pre>