repl/debugger integration

repl/debugger integration

[Andy Wingo]

Hi all,

A quick note to mention that I've pushed some patches that integrate the
debugger and the repl. Now if you have an error, you will be dropped
into a recursive repl:

    scheme@(guile-user)> (eval '(let a 10) (current-module))
    Throw to key `syntax-error':
    ERROR: In procedure macroexpand:
    ERROR: let: bad let in (let a 10)
    Entering a new prompt. Type `,bt' for a backtrace or `,q' to return to the old prompt.
    scheme@(guile-user) [1]> 

You see the [1] in the prompt, showing that you aren't at the bottom
level any more.

    scheme@(guile-user) [1]> ,help debug
    Debug Commands [abbrev]:

     ,backtrace [COUNT] [#:width W] [#:full? F]
                                 [,bt] - Print a backtrace.
     ,up [COUNT]                       - Select a calling stack frame.
     ,down [COUNT]                     - Select a called stack frame.
     ,frame [IDX]                [,fr] - Show a frame.
     ,procedure                [,proc] - Print the procedure for the selected frame.
     ,locals                           - Show local variables.

The commands that were part of the debugger are now meta-commands in the
repl:

    scheme@(guile-user) [1]> ,bt
    In ice-9/boot-9.scm:
     1056:  5 (#<procedure 3030ab0 ()>)
       61:  4 (call-with-prompt prompt0 #<procedure 2ee45e0 at syst...> #)
    In unknown file:
            3 (eval (let a 10) #<directory (guile-user) 2647510>)
    In ice-9/eval.scm:
      457:  2 (#<procedure 26537e0 at ice-9/eval.scm:451:4 (exp)> (# ...))
    In ice-9/psyntax.scm:
     1223:  1 (chi-top (let a 10) () ((top)) e (eval) (hygiene #))
    In unknown file:
            0 (scm-error syntax-error macroexpand "~a: ~a in ~a" (...) #f)

    scheme@(guile-user) [1]> ,frame
            0 (scm-error syntax-error macroexpand "~a: ~a in ~a" (...) #f)

    scheme@(guile-user) [1]> ,locals
      No local variables.

    scheme@(guile-user) [1]> ,up
    In ice-9/psyntax.scm:
     1223:  1 (chi-top (let a 10) () ((top)) e (eval) (hygiene #))

    scheme@(guile-user) [1]> ,locals
      Local variables:
      $1 = e = (let a 10)
      $2 = r = ()
      $3 = w = ((top))
      $4 = m = e
      $5 = esew = (eval)
      $6 = mod = (hygiene guile-user)
      $7 = type = core-form
      $8 = value = #<procedure 2614400 at ice-9/psyntax.scm:2078:19 (e r...>
      $9 = e = (let a 10)
      $10 = w = ((top))
      $11 = s = #f
      $12 = mod = (hygiene guile-user)
      $13 = x = #<undefined>

The module is whatever was current when the repl began. I don't think
the behavior of the "repl" command in the old debugger was very useful,
you often didn't have the bindings you expect -- though of course you
can switch modules while in the recursive repl. (Hm, should save the
module excursion there, I guess).

If you run debugging commands at the base repl you'll just get an error
message:

    scheme@(guile-user) [1]> ,q
    ERROR: In procedure macroexpand:
    ERROR: let: bad let in (let a 10)
    scheme@(guile-user)> ,bt
    Nothing to debug.

In the future we should be able to customize this behavior using repl
options (for example, a user should be able to say "always give me a
backtrace, but don't bother dropping me into a recursive
repl"). Feedback appreciated regarding what the default option should
be, of course. Or any other feedback folk might have is welcome.

Regards,

Andy
-- 
http://wingolog.org/

Re: repl/debugger integration

[Ludovic Courtès]

Hi Andy!

Andy Wingo <wingo@pobox.com> writes:

> A quick note to mention that I've pushed some patches that integrate the
> debugger and the repl. Now if you have an error, you will be dropped
> into a recursive repl:

I haven’t tried it yet but that looks excellent to me!

I’ve become fond of “recursive edits” in Emacs, and how convenient they
are when debugging something, so I’m enthusiastic about the recursive
REPL.

Thanks,
Ludo’.