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1
Print Hello World
Print a literal string on standard output 
write('Hello, world!\n')
Alternative implementation:
format("Hello world~n")
2
Print Hello 10 times
Loop to execute some code a constant number of times 
:- initialization(main).
main :- loop(10).

loop(0).
loop(N) :- N>0, write('Hello') , nl, N1 = N - 1, loop(N1).
12
Check if list contains a value
Check if the list contains the value x.
list is an iterable finite container. 
member(X, [One]).
13
Iterate over map keys and values
Access each key k with its value x from an associative array mymap, and print them. 
forall(get_dict(K, D, V),
       format("~w:~w~n", [K, V]))
19
Reverse a list
Reverse the order of the elements of the list x.
This may reverse "in-place" and destroy the original ordering. 
reverse(x, Reversed).
50
Make an infinite loop
Write a loop that has no end clause. 
repeat, write("hello\n").
Alternative implementation:
?- repeat, false.

% repeat/0 is built-in, but could be defined like this:
repeat.
repeat :- repeat.
Alternative implementation:
loop :- loop.

?- loop.
71
Echo program implementation
Basic implementation of the Echo program: Print all arguments except the program name, separated by space, followed by newline.
The idiom demonstrates how to skip the first argument if necessary, concatenate arguments as strings, append newline and print it to stdout. 
main(Argv) :- echo(Argv).

echo([]) :- nl.
echo([Last]) :- write(Last), echo([]).
echo([H|T]) :- write(H), write(' '), echo(T).
112
Iterate over map entries, ordered by keys
Print each key k with its value x from an associative array mymap, in ascending order of k. 
dict_pairs(D, _, Ps),
forall(member(K-V, Ps),
       format("~w:~w~n", [K, V]))
113
Iterate over map entries, ordered by values
Print each key k with its value x from an associative array mymap, in ascending order of x.
Multiple entries may exist for the same value x. 
dict_pairs(D, _, Ps),
transpose_pairs(Ps, TPs),
keysort(TPs, Val_sorted),
forall(member(V-K, Val_sorted),
       format("~w:~w~n", [V, K]))
117
Get list size
Set n to the number of elements of the list x. 
length(x, N).
314
Fill array with value
Set all the elements in the array x to the same value v 
set_all_elements_to_same_value(X, V) :-
    length(X, Length),
    length(FilledList, Length),
    maplist(=(V), FilledList, X).