Re: [Chicken-users] keyword args not assigned in program.

[Alan Post]

On Sat, Nov 20, 2010 at 04:00:26PM +0100, Felix wrote:
> From: Alan Post <address@hidden>
> Subject: [Chicken-users] keyword args not assigned in program.
> Date: Sat, 20 Nov 2010 06:59:38 -0700
> 
> > I'm dealing with a frustrating bug--I haven't been able to turn it
> > into a simple test case.  Will you let me explain what is going on,
> > why I haven't been able to make a test case, and then offer advice?
> > 
> > I have a compiler to convert a PEG grammar to scheme.  In my test
> > suite, I have a line:
> > 
> > <++> tests/run.scm
> >   (set! compiler (eval (compile "test.peg")))
> > <-->
> > 
> > The test.peg file references a symbol defined in tests/run.scm, and
> > I run the compiler with some sample data:
> > 
> > <++> tests/run.scm # this test fails!
> >   (define (transform #!rest rest #!key key0)
> >     (pretty-print rest)
> >     key0)
> > 
> >   (set! compiler (eval (compile "test.peg")))
> > 
> >   (compiler "a")
> > <-->
> > 
> > The compiler works, it calls |transform|, but the #!key arguments to
> > transform are not properly mapped.  |rest| is:
> > 
> >   (key0: 0 key1: 1)
> > 
> > but |key0| is:
> > 
> >   #f
> > 
> > So my #!rest arguments are seeing the tagged values, but the tagged
> > values aren't being assigned to #!key arguments.
> > 
> > That is simple enough to diagnose.  I've made my |test.peg| file,
> > the one I'm compiling, as simple as possible.  I want to remove the
> > compiler, because it is hands down the largest part of the test.
> > 
> > I run |(compile "teg.peg")| and save the output to |"out.scm"|,
> > converting my test to this:
> > 
> > <++> tests/run.scm # this test works!
> >   (define (transform #!rest rest #!key key0)
> >     (pretty-print rest)
> >     key0)
> > 
> >   (call-with-output-file "out.scm"
> >     (lambda (port)
> >       (write (compile "test.peg") port)))
> >   (set! compiler (eval (call-with-input-file "out.scm" read)))
> > 
> >   (compiler "a")
> > <-->
> > 
> > I have a temporary file that I write and then read.  The output of
> > the compiler is the same, but the method that the sexpr is evaluated
> > changes to have an intermediate file.
> > 
> > Suddenly, my test works and |key0| receives the correct value.
> > 
> > It appears that directly evaluating the result of the compiler causes
> > #!key arguments not to be assigned, but if I save that same result
> > and read it back in, things work fine.
> > 
> > What is going on?!  My closest guess is that I have some kind of gc
> > problem that I only trigger with a program of a particular size.  I'm
> > not sure where to go from here, as the test case is still a few
> > thousand lines of code, given that the compiler seems integral to
> > the test case.
> > 
> 
> How do the call-sites of `transform' look? Have you tried to
> trace `transform' (using the `trace' egg)? That way you can
> see how it is invoked. Don't worry about the GC - you would get
> much more weird errors than this.
> 

The trace resulting from the write/read/eval variation looks like
this:

  procedure (f_438 . args84)> (key0: 0 key1: 1))
  [0] (transform key0: 0 key1: 1)
  (key0: 0 key1: 1)
  [0] transform -> 0 

While the trace resulting from the (eval (compile ...)) looks like
this:

  procedure (f_438 . args84)> (key0: 0 key1: 1))
  [0] (transform key0: 0 key1: 1)
  (key0: 0 key1: 1)
  [0] transform -> #f 

The second form doesn't set key0, so it gets the default value of
#f.

Is there something else I can do to get better output from trace?

-Alan
-- 
.i ko djuno fi le do sevzi