(Prolog) Debug, to debug, debugging

Debugging is the process of removing runtime errors. This process can be aided by a debugger.

Typical predicates used are:

?trace and ?notrace
?spy and ?nospy

Example

The code below has a simulated error. Using a good debugger with the function 'Trace into' you can see that the call to doIt(5) checks doIt(1), doIt(2) and then ends at doIt(_).

PREDICATES
  nondeterm doIt(integer)
  
CLAUSES
  doIt(1) :-
    write("1"), nl,
    doit(5).
    
  doIt(2) :-
    write("2"), nl.
  doIt(3) :-
    write("3"), nl.
  doIt(4) :-
    write("4"), nl.
    
  doIt(_) :-
    write("ERROR"), nl.
    
   GOAL
     doIt(1).

Debugging function

% The clause 'trace' is a debugging function:
% * trace(integer DebugLevel, string Debugmessage)- (i,i)
%     * DebugLevel: only when below a certain value,
%       the DebugMessage will be stored
%     * DebugMessage: The message that will be appended to the file
%       'Trace.txt'
global domains
  FILE = myDebugFile
predicates
  trace(integer,String)- (i,i)
    
clauses
  trace(DebugLevel,DebugMessage) IF 
    DebugLevel < 50, % 50 is set as the default debug level
    openappend(myDebugFile,"Trace.txt"),
    writedevice(myDebugFile),
    write(DebugMessage),
    write("\n"),
    writedevice(stdout),
    closefile(myDebugFile),
    !.
  trace(_,_) IF
    % No problem, DebugLevel is too high
    !.
    
goal
  trace(1,"I am written to file."),
  trace(100,"I am not written to file.").

'Debug' links

last edited (December 6, 2006) by bilderbikkel, Number of views: 1609, Current Rev: 7 (Diff)

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