`(break)` does not work when placed in a file

[funk443]

As stated in the manual section 12.2, one can set a breakpoint in the program by placing a (break) procedure call, then the debugger will be invoked so one can inspect the continuation.

However, I found that when (break) is placed within a file, it simply quit the program, instead of invoking the debugger. Consider the following example:

(import (scheme))

(define x 100)
(break)
(display x)
(newline)

Run this file with scheme --debug-on-exception --program test.ss, the program simply exits upon (break), thus the remaining function calls will not be executed.

However, if I try to run this file in scheme REPL with (load "test.ss"), the debugger is invoked normally.

Is this an intented behaviour of (break) or not?

[burgerrg]

Thanks for finding the inconsistency in the behavior of break! It looks like the default break-handler was designed to raise the same kind of software interrupt that CTRL-C does, and new-cafe is designed to handle it. Since the program above is not run in a new-cafe REPL, the default interrupt handler calls reset, which simply exits.

[funk443]

So is a simple workaround to be changing the break-handler value, so it starts a new cafe?

[burgerrg]

Starting a new cafe won't reintroduce the break call. You could use raise-continuable instead, but it's clunky:

(import (scheme))

(define x 100)
(call/cc (lambda (k)
           (raise-continuable
            (condition
             (make-continuation-condition k)
             (make-message-condition "break")))))
(display x)
(newline)

% scheme --debug-on-exception --program test.ss
Exception: break
debug> i
#<continuation>                                                   : => (lambda (k) (k (void)))
100
% 

[funk443]

I see, thank you!