PrologT: A simple Prolog tracer

Instalation

You only need to download the files to a local folder. The tool requires SWI Prolog.

Use

A typical session looks like this:

swipl
Welcome to SWI-Prolog (threaded, 64 bits, version 8.2.4)
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software.
Please run ?- license. for legal details.

For online help and background, visit https://www.swi-prolog.org
For built-in help, use ?- help(Topic). or ?- apropos(Word).

?- [tracer].
true.

?- load('examples/ancestor.pl').
true.

?- run([ancestor(A,fanny)]).
ancestor(anna,fanny)
   parent(anna,fanny)
      mother(anna,fanny)
;
ancestor(daniel,fanny)
   parent(daniel,fanny)
      mother(daniel,fanny)
;
ancestor(tim,fanny)
   parent(tim,anna)
      mother(tim,anna)
   ancestor(anna,fanny)
      parent(anna,fanny)
         mother(anna,fanny)
;
ancestor(celine,fanny)
   parent(celine,daniel)
      father(celine,daniel)
   ancestor(daniel,fanny)
      parent(daniel,fanny)
         mother(daniel,fanny)

true.

If the example file contains a specification to "read" the atoms, then the trace above is formatted accordingly. For instance, given the following specifications

%!read mother(A,B) as: A is the mother of B
%!read father(A,B) as: A is the father of B
%!read parent(A,B) as: A is the parent of B
%!read ancestor(A,B) as: A is the ancestor of B

in file ancestor.pl, we get the following output instead:

anna is the ancestor of fanny
   anna is the parent of fanny
      anna is the mother of fanny
;
daniel is the ancestor of fanny
   daniel is the parent of fanny
      daniel is the mother of fanny
;
tim is the ancestor of fanny
   tim is the parent of anna
      tim is the mother of anna
   anna is the ancestor of fanny
      anna is the parent of fanny
         anna is the mother of fanny
;
celine is the ancestor of fanny
   celine is the parent of daniel
      celine is the father of daniel
   daniel is the ancestor of fanny
      daniel is the parent of fanny
         daniel is the mother of fanny

By default, the output is also saved in file temp.txt as follows:

[[[call(0,ancestor(anna,fanny),"anna is the ancestor of fanny"),call(1,parent(anna,fanny),"anna is the parent of fanny"),call(2,mother(anna,fanny),"anna is the mother of fanny")],[call(0,ancestor(daniel,fanny),"daniel is the ancestor of fanny"),call(1,parent(daniel,fanny),"daniel is the parent of fanny"),call(2,mother(daniel,fanny),"daniel is the mother of fanny")],[call(0,ancestor(tim,fanny),"tim is the ancestor of fanny"),call(1,parent(tim,anna),"tim is the parent of anna"),call(2,mother(tim,anna),"tim is the mother of anna"),call(1,ancestor(anna,fanny),"anna is the ancestor of fanny"),call(2,parent(anna,fanny),"anna is the parent of fanny"),call(3,mother(anna,fanny),"anna is the mother of fanny")],[call(0,ancestor(celine,fanny),"celine is the ancestor of fanny"),call(1,parent(celine,daniel),"celine is the parent of daniel"),call(2,father(celine,daniel),"celine is the father of daniel"),call(1,ancestor(daniel,fanny),"daniel is the ancestor of fanny"),call(2,parent(daniel,fanny),"daniel is the parent of fanny"),call(3,mother(daniel,fanny),"daniel is the mother of fanny")]]

The tracer can also be used as a shell command:

$ ./tracer_shell.pl 'examples/ancestor.pl' -g '[ancestor(A,fanny)]'

By default, the output in file temp.txt is the same as above. Alternatively, one can add -o text to get a textual representation instead (the same representation that is shown on the screen).

Comments or questions are welcome: [email protected].