Easily Using SWI-Prolog within Matlab

This post intends to show how to interact with SWI-Prolog codes inside MatLab.

The following code is an arbitrary example of a special system, which covers different situations for “control” based on various inputs.

:- dynamic upOn/0, upOff/0.


getOn(sensor,Value) :- Value < 0.5.
getOff(sensor,Value) :- Value > 0.5. 

setOn(valve,Value) :- Value is 1.0.
setOff(valve,Value) :- Value is 0.0.

control(V_in,V_out,S0,S1,S2,SW) :- getOff(sensor,SW),getOff(sensor,S0),getOff(sensor,S1),getOff(sensor,S2),upOff,setOff(valve,V_in),setOff(valve,V_out).
control(V_in,V_out,S0,S1,S2,SW) :- getOn(sensor,SW),getOff(sensor,S0),getOff(sensor,S1),getOff(sensor,S2),upOff,setOn(valve,V_in),setOff(valve,V_out),retract(upOff),asserta(upOn).
control(V_in,V_out,S0,S1,S2,SW) :- getOn(sensor,SW),getOn(sensor,S0),getOff(sensor,S1),getOff(sensor,S2),upOn,setOn(valve,V_in),setOff(valve,V_out).
control(V_in,V_out,S0,S1,S2,SW) :- getOn(sensor,SW),getOn(sensor,S0),getOn(sensor,S1),getOff(sensor,S2),upOn,setOn(valve,V_in),setOff(valve,V_out).
control(V_in,V_out,S0,S1,S2,SW) :- getOn(sensor,SW),getOn(sensor,S0),getOn(sensor,S1),getOn(sensor,S2),upOn,setOff(valve,V_in),setOn(valve,V_out),retract(upOn),asserta(upOff).
control(V_in,V_out,S0,S1,S2,SW) :- getOn(sensor,SW),getOn(sensor,S0),getOn(sensor,S1),getOn(sensor,S2),upOff,setOff(valve,V_in),setOn(valve,V_out).
control(V_in,V_out,S0,S1,S2,SW) :- getOn(sensor,SW),getOn(sensor,S0),getOn(sensor,S1),getOff(sensor,S2),upOff,setOff(valve,V_in),setOn(valve,V_out).
control(V_in,V_out,S0,S1,S2,SW) :- getOn(sensor,SW),getOn(sensor,S0),getOff(sensor,S1),getOff(sensor,S2),upOff,setOn(valve,V_in),setOff(valve,V_out),retract(upOff),asserta(upOn).
control(V_in,V_out,S0,S1,S2,SW) :- getOff(sensor,SW),getOn(sensor,S0),getOn(sensor,S1),getOn(sensor,S2),setOff(valve,V_in),setOn(valve,V_out).
control(V_in,V_out,S0,S1,S2,SW) :- getOff(sensor,SW),getOn(sensor,S0),getOn(sensor,S1),getOff(sensor,S2),upOff,setOff(valve,V_in),setOn(valve,V_out).
control(V_in,V_out,S0,S1,S2,SW) :- getOff(sensor,SW),getOn(sensor,S0),getOn(sensor,S1),getOff(sensor,S2),upOn,setOff(valve,V_in),setOn(valve,V_out),retract(upOn),asserta(upOff).
control(V_in,V_out,S0,S1,S2,SW) :- getOff(sensor,SW),getOn(sensor,S0),getOff(sensor,S1),getOff(sensor,S2),upOff,setOff(valve,V_in),setOn(valve,V_out).
control(V_in,V_out,S0,S1,S2,SW) :- getOff(sensor,SW),getOn(sensor,S0),getOff(sensor,S1),getOff(sensor,S2),upOn,setOff(valve,V_in),setOn(valve,V_out),retract(upOn),asserta(upOff).

The above code can be called by another Prolog script as follows:

#!/usr/bin/env swipl

:- initialization main. 

main:-  current_prolog_flag(argv,Argv),
        nth0(0, Argv, A), % get first argument
		nth0(1, Argv, B), % get second argument
		nth0(2, Argv, C), % get third argument
		nth0(3, Argv, D), % get fourth argument
		format("~w ~w ~w ~w \n",[A,B,C,D]), % Print inputs
        consult('example1Prolog'), % Load main Prolog code
		atom_number(A,E), % Transform inputs into Prolog integers
		control(X,Y,E,F,G,H), % Query control function with inputs
		format("X= ~w Y= ~w \n",[X,Y]),	% Prints output variables
		halt. % Finishes execution

The script is executed with the bash shell command:

swipl -s plscript.pl 1 1 1 1

Where the last 4 numbers stand for the Prolog code inputs. The following output with the above command is:

1 1 1 1
X= 0.0 Y= 1.0

Most of the work is already done! (WOW). The last step is executing the same bash command within Matlab using the “system” function:

[status,term_out] = system('swipl -s plscript.pl 1 1 1 1')

“term_out” variable will hold the script output for the inputs given. The following picture shows the previous call output on the main console with the described method.


Note: It is important to check if a set of inputs will return valid outputs for the system (if they are covered). Also, make sure to test if the script is reaching the last line “halt.”, otherwise the SWI-Prolog will open without closing and the Matlab will wait until the application finishes (never) and crash.

The following Prolog command is helpful if the developed Prolog code depends on dynamic variables like the one shown in this tutorial:


The problem is that the saved data can not be loaded into a running environment, making this post approach not to work for dynamic variables (for now).

Files can be accessed at:


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