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(Debug on Error): Added paragraph on need to use

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debugging evaluator.  Added text on what the Guile REPL code does.
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Neil Jerram 2006-08-29 22:47:41 +00:00
parent b5944f6672
commit 5b2da4cc18
2 changed files with 29 additions and 4 deletions
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5
doc/ref/ChangeLog
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@ -1,3 +1,8 @@
2006-08-29 Neil Jerram <neil@ossau.uklinux.net>
* api-debug.texi (Debug on Error): Added paragraph on need to use
debugging evaluator. Added text on what the Guile REPL code does.
2006-08-28 Neil Jerram <neil@ossau.uklinux.net>
* api-debug.texi (Examining the Stack): Minor improvements to

28
doc/ref/api-debug.texi
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@ -447,10 +447,19 @@ The other interesting information about an error is the full Scheme
stack at the point where the error occurred; in other words what
innermost expression was being evaluated, what was the expression that
called that one, and so on. If you want to write your code so that it
captures and can display this information as well, there are two
captures and can display this information as well, there are three
important things to understand.
Firstly, the stack at the point of the error needs to be explicitly
Firstly, the code in question must be executed using the debugging
version of the evaluator, because information about the Scheme stack is
only available at all from the debugging evaluator. Using the debugging
evaluator means that the debugger option (@pxref{Debugger options})
called @code{debug} must be enabled; this can be done by running
@code{(debug-enable 'debug)} or @code{(turn-on-debugging)} at the top
level of your program; or by running guile with the @code{--debug}
command line option, if your program begins life as a Scheme script.
Secondly, the stack at the point of the error needs to be explicitly
captured by a @code{make-stack} call (or the C equivalent
@code{scm_make_stack}). The Guile library does not do this
``automatically'' for you, so you will need to write code with a
@ -464,7 +473,7 @@ running on top of the Guile library, and which uses @code{catch} and
@code{make-stack} in the way we are about to describe to capture the
stack when an error occurs.)
Secondly, in order to capture the stack effectively at the point where
Thirdly, in order to capture the stack effectively at the point where
the error occurred, the @code{make-stack} call must be made before Guile
unwinds the stack back to the location of the prevailing catch
expression. This means that the @code{make-stack} call must be made
@ -574,7 +583,14 @@ application frame -- that is, a frame that satisfies the
@subsubsection What the Guile REPL does
[To be completed]
The Guile REPL code (in @file{ice-9/boot-9.scm}) uses a @code{catch}
with a pre-unwind handler to capture the stack when an error occurs in
an expression that was typed into the REPL, and saves the captured stack
in a fluid (@pxref{Fluids and Dynamic States}) called
@code{the-last-stack}. You can then use the @code{(backtrace)} command,
which is basically equivalent to @code{(display-backtrace (fluid-ref
the-last-stack))}, to print out this stack at any time until it is
overwritten by the next error that occurs.
@deffn {Scheme Procedure} backtrace [highlights]
@deffnx {C Function} scm_backtrace_with_highlights (highlights)
@ -585,6 +601,10 @@ it should be a list; the elements of this list will be
highlighted wherever they appear in the backtrace.
@end deffn
You can also use the @code{(debug)} command to explore the saved stack
using an interactive command-line-driven debugger. See @ref{Interactive
Debugger} for more information about this.
@deffn {Scheme Procedure} debug
Invoke the Guile debugger to explore the context of the last error.
@end deffn