Checkpoint

examples/scratchpad.pl

@@ -1,27 +1,32 @@
 % choice(X) :- X = 1, !; X = 2.
-grade(alice, a).
-grade(bob, b).
-grade(carol, a).
-grade(dave, c).
+:- dynamic declaration/1.
 
-got_an_a(Student) :-
-    grade(Student, Grade),
-    Grade = a.
+add_declaration_first(NewDecl) :-
+    asserta(declaration(NewDecl)).
 
-did_not_get_an_a(Student) :-
-    grade(Student, Grade),
-    Grade \= a.
+add_declaration_last(NewDecl) :-
+    assertz(declaration(NewDecl)).
+
+database :-
+    add_declaration_first('Man is born free, and everywhere he is in chains.'),
+    retract(declaration(_)),
+    add_declaration_last('The revolution devours its own children.'),
+    add_declaration_first('I disapprove of what you say, but I will defend to the death your right to say it.'),
+    add_declaration_first('Give me Liberty, or give me Death!'),
+    add_declaration_last('So this is how liberty dies, with thunderous applause.').
+
+show_declarations :-
+    declaration(Decl),
+    write(Decl), nl,
+    fail.
+
+show_declarations.
 
 :- initialization(main).
 
 main :-
-    write("While "),
-    got_an_a(X),
-    write(X), write(" got an A, "), fail;
-    write("but "),
-    did_not_get_an_a(Y),
-    write(Y), write(" did not get an A, "), fail; write("unfortunately."), nl.
+    database,
+    show_declarations,
+    retractall(declaration(_)),
+    show_declarations.
 
-:- initialization(main).
-main :- write('gpl zegt: '), groet(wereld), nl.
-groet(X) :- write(dag(X)).