Obtaining and Installing Guile
******************************

Here is the information you will need to get and install Guile and extra packages and documentation you might need or find interesting.

The Basic Guile Package
=======================

Guile can be obtained from the main GNU archive site ftp://prep.ai.mit.edu/pub/gnu or any of its mirrors.  The file will be named guile-version.tar.gz.  The current version is VERSION, so the file you should grab is:

ftp://prep.ai.mit.edu/pub/gnu/guile-VERSION.tar.gz

To unbundle Guile use the instruction

     zcat guile-VERSION.tar.gz | tar xvf -

which will create a directory called guile-VERSION with all the sources.  You can look at the file INSTALL for detailed instructions on how to build and install Guile, but you should be able to just do

     cd guile-VERSION
     ./configure
     make install

This will install the Guile executable guile, the Guile library libguile.a and various associated header files and support libraries. It will also install the Guile tutorial and reference manual.

Since this manual frequently refers to the Scheme ``standard'', also known as R4RS, or the ``Revised^4 Report on the Algorithmic Language Scheme'', we have included the report in the Guile distribution; see Introduction (Revised(4) Report on the Algorithmic Language Scheme). This will also be installed in your info directory.

Packages not shipped with Guile
===============================

We ship the Guile tutorial and reference manual with the Guile distribution [FIXME: this is not currently true (Sat Sep 20 14:13:33 MDT 1997), but will be soon.]  Since the Scheme standard (R4RS) is a stable document, we ship that too.

Here are references (usually World Wide Web URLs) to some other freely redistributable documents and packages which you might find useful if you are using Guile.

SCSH
     the Scheme Shell.  Gary Houston has ported SCSH to Guile.  The relevant chapter (see The Scheme shell (scsh)) has references to the SCSH web page with all its documentation.

SLIB
     a portable Scheme library maintained by Aubrey Jaffer.  SLIB can be obtained by ftp from ftp://prep.ai.mit.edu/pub/gnu/jacal/.

     The SLIB package should be unpacked somewhere in Guile's load path.  It will typically be unpacked in /usr/local/share/guile/site, so that it will be /usr/local/share/guile/site/slib.

     Guile might have been installed with a different prefix, in which case the load path can be checked from inside the interpreter with:

          guile> %load-path
          ("/usr/local/share/guile/site" "/usr/local/share/guile/1.3a" "/usr/local/share/guile" ".")

     The relevant chapter (see SLIB) has details on how to use SLIB with Guile.

JACAL
     a symbolic math package by Aubrey Jaffer.  The latest version of Jacal can be obtained from ftp://prep.ai.mit.edu/pub/gnu/jacal/, and should be unpacked in /usr/local/share/guile/site/slib so that it will be in /usr/local/share/guile/site/slib/jacal.

     The relevant section (see JACAL) has details on how to use Jacal.

Debugger User Interface
***********************

When debugging a program, programmers often find it helpful to examine the program's internal status while it runs: the values of internal variables, the choices made in if and cond statements, and so forth.  Guile Scheme provides a debugging interface that programmers can use to single-step through Scheme functions and examine symbol bindings.  This is different from the Debugging, which permits programmers to debug the Guile interpreter itself.  Most programmers will be more interested in debugging their own Scheme programs than the interpreter which evaluates them.

[FIXME: should we include examples of traditional debuggers and explain why they can't be used to debug interpreted Scheme or Lisp?]

Single-Step
===========

Trace
=====

When a function is traced, it means that every call to that function is reported to the user during a program run.  This can help a programmer determine whether a function is being called at the wrong time or with the wrong set of arguments.

 -- Function: trace function
     Enable debug tracing on function.  While a program is being run, Guile will print a brief report at each call to a traced function, advising the user which function was called and the arguments that were passed to it.

 -- Function: untrace function
     Disable debug tracing for function.

Example:

     (define (rev ls)
       (if (null? ls)
           '()
           (append (rev (cdr ls))
                   (cons (car ls) '())))) => rev

     (trace rev) => (rev)

     (rev '(a b c d e))
     => [rev (a b c d e)]
        |  [rev (b c d e)]
        |  |  [rev (c d e)]
        |  |  |  [rev (d e)]
        |  |  |  |  [rev (e)]
        |  |  |  |  |  [rev ()]
        |  |  |  |  |  ()
        |  |  |  |  (e)
        |  |  |  (e d)
        |  |  (e d c)
        |  (e d c b)
        (e d c b a)
        (e d c b a)

Note the way Guile indents the output, illustrating the depth of execution at each function call.  This can be used to demonstrate, for example, that Guile implements self-tail-recursion properly:

     (define (rev ls sl)
       (if (null? ls)
           sl
           (rev (cdr ls)
                (cons (car ls) sl)))) => rev

     (trace rev) => (rev)

     (rev '(a b c d e) '())
     => [rev (a b c d e) ()]
        [rev (b c d e) (a)]
        [rev (c d e) (b a)]
        [rev (d e) (c b a)]
        [rev (e) (d c b a)]
        [rev () (e d c b a)]
        (e d c b a)
        (e d c b a)

Since the tail call is effectively optimized to a goto statement, there is no need for Guile to create a new stack frame for each iteration.  Using trace here helps us see why this is so.

Backtrace
=========

Stacks and Frames
=================

When a running program is interrupted, usually upon reaching an error or breakpoint, its state is represented by a stack of suspended function calls, each of which is called a frame.  The programmer can learn more about the program's state at the point of interruption by inspecting and modifying these frames.

 -- primitive: stack? obj
     Return #t if OBJ is a calling stack.

 -- primitive: make-stack

 -- syntax: start-stack id exp
     Evaluate EXP on a new calling stack with identity ID.  If EXP is interrupted during evaluation, backtraces will not display frames farther back than EXP's top-level form.  This macro is a way of artificially limiting backtraces and stack procedures, largely as a convenience to the user.

 -- primitive: stack-id stack
     Return the identifier given to STACK by start-stack.

 -- primitive: stack-ref

 -- primitive: stack-length

 -- primitive: frame?

 -- primitive: last-stack-frame

 -- primitive: frame-number

 -- primitive: frame-source

 -- primitive: frame-procedure

 -- primitive: frame-arguments

 -- primitive: frame-previous

 -- primitive: frame-next

 -- primitive: frame-real?

 -- primitive: frame-procedure?

 -- primitive: frame-evaluating-args?

 -- primitive: frame-overflow