Put a breakpoint at the indicated source-location. File is a current
sourcefile (as reported by source_file/1). Line is the 1-based line
in which Char is. Char is the position of the break.
First, '$clause_from_source'/4 uses the SWI-Prolog clause-source
information to find the last clause starting before Line.
'$break_pc' generates (on backtracking), a list of possible
Note that in addition to setting the breakpoint, the system must be
in debug mode for the breakpoint to take effect. With threading
enabled, there are various different ways this may be done. See
debug/0, tdebug/0 and tdebug/1. Therefore, this predicate does not
enable debug mode.