Extending apply

[Ian Grant]

Dear, happy guile-users

The scmutils package for SICM allows one to do things like apply arguments to 
a vector which evaluates to a vector of results of applying the arguments to 
each element in turn. It achieves this in MIT-scheme using this 
kludgey-looking method. Here g:apply does the actual extended application. I 
am not entirely sure about how the stack-frame methods work, but I guess it's 
looking forward from the continuation of the top-level call to apply.

Has anyone done anything like this with guile using the evaluator trap options 
or something?

I suppose an alternative would be to run a different REPL ... but maybe that 
would be harder.

Any ideas gratefully accepted.

Best wishes
Ian

(define *enable-generic-apply* true)

(define inapplicable-object/operator
  (condition-accessor condition-type:inapplicable-object 'DATUM))

(define (apply-extension-init)
  (bind-default-condition-handler
   (list condition-type:inapplicable-object)
   (lambda (condition)
     (if *enable-generic-apply*
         ((stack-frame->continuation
           (stack-frame/next
            (stack-frame/next
             (stack-frame/next
              (continuation->stack-frame
               (condition/continuation condition))))))
          (lambda args
            (g:apply (inapplicable-object/operator condition) args)))))))

(define (once-only! thunk name)
  (if (lexical-unbound? system-global-environment name)
      (begin (thunk)
             ;; Create NAME in SGE
             (eval `(define ,name #t) system-global-environment)
             'done)
      'already-done))

(once-only! apply-extension-init 'apply-extension-init)