Hi all,
I was playing around with elisp macros in an org-file and came across a
behavior I didn't expect that is due to lexical binding.
Here is the code:
#+BEGIN_SRC emacs-lisp :results output :prologue
;; -*- lexical-binding: t -*-
;; you need this to make the binding.
(setq lexical-binding t)
;; Graham's alambda
(defmacro alambda (parms &rest body)
`(cl-labels ((self ,parms ,@body))
#'self))
(setq
N
(alambda (n)
(if (> n 0)
(cons
n
(self (- n 1))))))
(funcall N 3)
#+END_SRC
The last line should return (3 2 1), and it does if I use C-x C-e on
each form. If I try to run the block though, I get an error:
cons: Symbol’s value as variable is void: --cl-self--
I can see where that comes from. The macro expands to:
(lambda (n) (if (> n 0) (cons n (funcall --cl-self-- (- n 1)))))
This doesn't work because babel simply evals the body of the code. It
turns out you can use eval with lexical scoping:
(eval FORM &optional LEXICAL)
Evaluate FORM and return its value.
If LEXICAL is t, evaluate using lexical scoping.
So, I would like to propose adding the third argument to the eval
statement that reads
(assoc :lexical params)
to turn on lexical eval if you want it.
What do you think?
--
Professor John Kitchin
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803
@johnkitchin
http://kitchingroup.cheme.cmu.edu
