Stepping through program execution and breaking at predefined conditions is possible with the MINERVA debugger.

The debugger is operationally simple and compiled right into the MINERVA binary (for techies: its not a meta-program).

To compile a program fragment for execution under the MINERVA debugger use minervac -debug.

The following example shows the use of breakpoint and the invokation. For details refer to Compile, Go and the other files of this directory.

start :-
	breakpoint(app/3),			% Breakpoint
	breakif((app(A,B,C) :- C = [c])),	% Condition
	debug(app([1,2], [ b,c], L)).		% Invokation

app([],L,L).
app([E|L1],L2,[E|L3]) :- app(L1,L2,L3).

This is how a first step and the the help screen look like:

MINERVA 2.1 Development Server              (c) 1996,99 IF Computer
http://www.ifcomputer.com/MINERVA     mailto:support@ifcomputer.com
MINERVA License for evaluation purposes only

?- start.
CALL  app([1,2],[b,c],_554)
trace: h
s)tep        single pass
n)ext        pass over
f)ail        force 'fail'
c)ont        continue till next breakpoint
b)acktrace   show stack backtrace (activation stack)
a)bort       abort
e)scape      call 'break/0'
h)elp        show this help message

app([1,2],[b,c],_554)
trace: