debugging help: how to read/use a backtrace?

[Jan Nieuwenhuizen]

Hi,

I often find myself struggling to pinpoint an error location from
Guile's backtrace (see below) and I am starting to wonder if there is
something that I'm missing.

Usually I can guess.  If not, I scatter the code with debug printing
before and after statements

   (let* ((x ...)
          (foo (format (current-error-port) "00=~a\n" x))
          (y ..)
          (foo (format (current-error-port) "01=~a\n" y))

to find the problematic call.

Looking at the trace below, I see only one possible indirect indicator
of where this error occurs: the `In unknown file' bit.  All the others
are srfi/srfi-1.scm and ice-9/eval.scm.  So my starting point is

    In unknown file:
               0 (_ () () 0 1)

Hmm.  Originally it read

    0 (_ () () 0 0)

because I already started by modifying my source code and change all the
places that match such a call, modifying the last zero with a unique
integer (which will produce incorrect results, of course), like so

    (append-map (lambda/label->list '() '() 0 1) o))
    ...
    (offset (if prefix (length (functions->text (cdr prefix) '() 0 2))
    ...
    (t ((lambda/label->list '() '() 0 3) l/l))

ETC.

That helps me to identify the source location and then I can add debug
printing

    (define (lambda/label->list f g t d)
      (lambda (l/l)
        (format (current-error-port) "l/l=~a\n" l/l)
        (format (current-error-port) "gonna exec =~a\n" (procedure? l/l))
        (if (procedure? l/l) (format (current-error-port) "source=~a\n" 
(procedure-source l/l)))
        (if (not (procedure? l/l)) '() (l/l f g t d))
        (format (current-error-port) "done\n" )
        (if (not (procedure? l/l)) '() (l/l f g t d))))

But here it stops again... (procedure-source l/l) yields #f, so all I
know is that I create a lambda somewhere that tries to invoke the string
"eval_apply".  How can I get some help to find the source location of
that?

Greetings,
Jan


l/l=#<procedure 13000a0 at ice-9/eval.scm:342:13 (a b c d)>
gonna exec =#t
source=#f
Backtrace:
In srfi/srfi-1.scm:
   592:29 19 (map1 (#<procedure 19c30c0 at ice-9/eval.scm:342:13 (a b c d)> 
#<p?> ?))
   592:29 18 (map1 (#<procedure 1adbd20 at ice-9/eval.scm:342:13 (a b c d)> 
#<p?> ?))
   592:29 17 (map1 (#<procedure 15201c0 at ice-9/eval.scm:342:13 (a b c d)> 
#<p?> ?))
   592:29 16 (map1 (#<procedure 1530980 at ice-9/eval.scm:342:13 (a b c d)> 
#<p?> ?))
   592:29 15 (map1 (#<procedure 1be2e40 at ice-9/eval.scm:342:13 (a b c d)> 
#<p?> ?))
   592:29 14 (map1 (#<procedure 1be2620 at ice-9/eval.scm:342:13 (a b c d)> 
#<p?> ?))
   592:29 13 (map1 (#<procedure 1548820 at ice-9/eval.scm:342:13 (a b c d)> 
#<p?> ?))
   592:29 12 (map1 (#<procedure 1548660 at ice-9/eval.scm:342:13 (a b c d)> 
#<p?> ?))
   592:29 11 (map1 (#<procedure 1577980 at ice-9/eval.scm:342:13 (a b c d)> 
#<p?> ?))
   592:29 10 (map1 (#<procedure 1577820 at ice-9/eval.scm:342:13 (a b c d)> 
"ap?" ?))
   592:29  9 (map1 ("apply" #<procedure 13000a0 at ice-9/eval.scm:342:13 (a b 
c?> ?))
   592:17  8 (map1 (#<procedure 13000a0 at ice-9/eval.scm:342:13 (a b c d)> 
#<pr?>))
In ice-9/eval.scm:
    608:8  7 (_ #(#(#<directory (mes elf-util) ec6000> () () 0 1) #<procedure 
13?>))
   293:34  6 (_ #(#(#<directory (mes libc-i386) f39d80>) () () 0 1 0 ((#<p?> ?) 
?)))
In srfi/srfi-1.scm:
   679:15  5 (append-map _ _ . _)
   592:17  4 (map1 ((#<procedure 1a2ef40 at ice-9/eval.scm:342:13 (a b c d)> # 
?) ?))
   679:15  3 (append-map _ _ . _)
   592:29  2 (map1 (#<procedure 1a2ef40 at ice-9/eval.scm:342:13 (a b c d)> 
"ev?" ?))
   592:17  1 (map1 ("eval_apply" #<procedure 1a41b20 at ice-9/eval.scm:342:13 
(?> ?))
In unknown file:
           0 (_ () () 0 1)

ERROR: ERROR: Wrong type to apply: "eval_apply"

-- 
Jan Nieuwenhuizen <address@hidden> | GNU LilyPond http://lilypond.org
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