Utilities.md

Utilities

Write on the console

?- nl. % new line, returns true.
?- write('a').
?- write(3).
?- X is 3 + 5, write(X).

Clear the console

% define this rule at the top of the .pl file, then call it like 
% ?- cls.
cls :- write('\e[2J').

Comments

% Single line comment 
/* 
Mutli
Line 
comment 
*/

Reload the file in prolog

?- make.

Assertion

?- assert(ite_student(ahmad)).
?- assert(happy(X) :- ite_student(X)).
?- happy(ahmad). % will return true

Retracting

?- retract(ite-student(ahmad)).
?- retract(happy(X) :- ite-student(X)).
?- happy(ahmad). % will return false

Close the command-line

halt.

If an exception occurs, type a to start a new query.

Read user input example

write('Enter the first number: '), read(FirstNumber).

Negation

\+ rule.
not(rule).

Debugging

Swi-Prolog -> Debug -> Graphical Debugger -> ?- trace. -> some query -> use the arrows to step in/over the code.

Unit Testing

• See testing_demo

Conditional-expression

(if -> then; else) beware about the syntax

?- 3 =\= 4 % numeric comparasion
%    true
?- 4 =\= 4
%    false
?- ahmad \= ahmad. % string comparasion
%    false
?- ahmad \= khaled.
%    true
?- ahmad = ahmad
%    true
?- (b\=a -> A=1; A=0)
%    A = 1
?- (a\=a -> A=1; A=0)
%    A = 0

Configuring the console!

With colors

?- ansi_format([fg(red)], 'This is in red', []).
% black, red, green, yellow, blue, magenta, cyan, white
?- ansi_format([bg(cyan)], 'This has a cyan background', []).
?- ansi_format([bg(cyan),fg(magenta),bold], 'We can mix them', []).
% reset, bold, fg(Color), bg(Color),...
?- ansi_format([], 'This also formats the string (~w = 5)', [5]).

Enable dark mode

:- use_module(library(theme/dark)).
% Or in the terminal/console
?- use_module(library(theme/dark)).