Re: [Sbcl-devel] [Patch] Control trapping of macroexpand errors

[Willem B. <met...@gm...>]

On Sat, May 17, 2008 at 3:12 PM, Richard M Kreuter <kr...@pr...> wrote:
> "Willem Broekema" writes:
>> In CLPython, certain Python syntax errors are detected during
>> macroexpansion, and they throw my own SyntaxError condition. I'd like
>> to handle these errors myself, instead of having the SBCL compiler
>> catch and report them. The below patch makes that possible, by
>> introducing the boolean *trap-macroexpand-errors*.

> I may be misunderstanding your proposed change, but can't you use
> *MACROEXPAND-HOOK* to set up your custom error handling?  The following
> seems to be a start:
>
> * (defvar *initial-macroexpand-hook* *macroexpand-hook*)
>
> *INITIAL-MACROEXPAND-HOOK*
> * (setq *macroexpand-hook*
>        #'(lambda (expander form env)
>            (handler-bind ((error (lambda (e)
>                                    ;; Your stuff could go here.
>                                    (invoke-debugger e))))
>              (funcall *initial-macroexpand-hook* expander form env))))

This would work if I always want to enter the debugger, when a macro
gave SyntaxError. That is not the case, as there could be a handler
for the condition outside the call to compile, like:

(handler-case (compile nil '(lambda () (python-code)))
    (SyntaxError (c) ...)) ;; detected in macroexpansion

Maybe you took the "myself" in "I'd like to handle these
[SyntaxErrors] myself" a bit more literal than intended. :)

- Willem