3.4.2.2 Source Breakpoints

A source breakpoint is a breakpoint that triggers whenever program execution hits a particular source location. A source breakpoint can be conveniently set simply by evaluating code that has ## inserted into it at the position where you want the breakpoint to be.

For example, to set a breakpoint immediately before evaluation of (= n 0) in the following procedure definition, evaluate:

     (define (fact1 n)
       (if ##(= n 0)
           1
           (* n (fact1 (- n 1)))))
     -|
     Set breakpoint 1: standard input:4:9: (= n 0)

Note the message confirming that you have set a breakpoint. If you don't see this, something isn't working.

## is provided by the (ice-9 debugger breakpoints source) module, so you must use this module before trying to set breakpoints in this way:

     (use-modules (ice-9 debugger breakpoints source))

You may like to add this to your .guile file.

The default behaviour for source breakpoints is debug-here (see Breakpoint Behaviours), which means to enter the command line debugger when the breakpoint is hit. So, if you now use fact1, that is what happens.

     guile> (fact1 3)
     Hit breakpoint 1: standard input:4:9: (= n 0)
     Frame 3 at standard input:4:9
             (= n 0)
     debug>