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prolog_breakpoints.pl -- Manage Prolog break-points
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This module provides an interface for development tools to set and delete break-points, giving a location in the source. Development tools that want to track changes to breakpoints must use user:message_hook/3 to intercept these message terms:

  • breakpoint(set, Id)
  • breakpoint(delete, Id)

Note that the hook must fail after creating its side-effects to give other hooks the opportunity to react.

Source set_breakpoint(+File, +Line, +Char, -Id) is det
Source set_breakpoint(+Owner, +File, +Line, +Char, -Id) is det
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' generated (on backtracking), a list of possible break-points.

Note that in addition to setting the break-point, 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.

Owner- denotes the file that owns the clause. set_breakpoint/5 is used to set breakpoints in an included file in the context of the Owner main file. See source_file_property/2.
Source delete_breakpoint(+Id) is det
Delete breakpoint with given Id. If successful, print_message(breakpoint(delete, Id)) is called. Message hooks working on this message may still call breakpoint_property/2.
- existence_error(breakpoint, Id).
Source breakpoint_property(?Id, ?Property) is nondet
True when Property is a property of the breakpoint Id. Defined properties are:
Provided if the breakpoint is in a clause associated to a file. May not be known.
Line of the breakpoint. May not be known.
character_range(Start, Len)
One-based character offset of the break-point. May not be known.
Reference of the clause in which the breakpoint resides.
Source user:prolog_event_hook(+Break)[multifile]
Handle callEventHook() from '$break_at'/3. This hook is called with signal handling disabled, i.e., as an atomic action.