(defun foo (x)
(wrapper-macro
(bar 42 x)))
Where wrapper-macro simply prints ‘Normal exit’ or ‘Throw’ as control returns from bar through foo. (If bar returns normally, all the return values are returned from foo after wrapper-macro prints. If bar exits via a throw, then the throw continues after wrapper-macro prints.)The challenge: Implement
wrapper-macro.(If you wish, imagine that
wrapper-macro simply expands to this:
(defun foo (x)
(wrapper-function
(lambda ()
(bar 42 x))))
and the challenge is to implement wrapper-function.)
4 comments:
(defun wrapper-function (thunk)
(let ((return? nil))
(unwind-protect
(multiple-value-prog1
(funcall thunk)
(setf return? t))
(if return?
(print "Return")
(print "Non-local exit")))))
Btw, if possible, please allow the use of PRE tags in comments in order to display code fragments properly
I wish I could turn on PRE tags.
If you untabify and replace the spaces with , you get this:
(defun wrapper-function (thunk)
(let ((return? nil))
(unwind-protect
(multiple-value-prog1
(funcall thunk)
(setf return? t))
(if return?
(print "Return")
(print "Non-local exit")))))
I might be wrong, but can't you just do it with call/cc and modifying bar function to use continuations?
ohw0w said...
Can't you just do it with call/cc and modifying bar function to use continuations?
Yikes! I don't think you need to haul out the heavy machinery!
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