* Procedure (closure) using a macro fails to work after byte-compilation
@ 2016-08-04 14:24 Alex Vong
2016-08-06 23:32 ` Michael Heerdegen
0 siblings, 1 reply; 2+ messages in thread
From: Alex Vong @ 2016-08-04 14:24 UTC (permalink / raw)
To: help-gnu-emacs
Hi,
I am trying to simulate proper tail recursion in emacs, so I write a
custom macro that does the same as `letrec'. Following this textbook
implementation in Scheme:
(define-syntax letrec
(syntax-rules ()
((_ ((var init) ...) . body)
(let ((var 'undefined) ...)
(let ((var (let ((temp init)) (lambda () (set! var temp))))
...
(bod (lambda () . body)))
(var) ... (bod))))))
I wrote:
;; Note that we have to `(setq lexical-binding t)' before doing
;; anything. Also, the macro is a simplified version of the real one.
(defmacro letrec2 (bindings form &rest forms)
(declare (indent defun))
(let* ((uninit-bindings ; Produce s-exp to produce uninitialized bindings.
(cl-mapcar (lambda (binding)
(pcase-let ((`(,name ,_) binding))
`(,name (cl-gensym))))
bindings))
;; Produce s-exp to produce thunks for doing assignment.
(assign-thunks
(cl-mapcar (lambda (binding)
(pcase-let ((temp (cl-gensym))
(`(,var ,init) binding))
`(,var
(let ((,temp ,init))
(lambda ()
(setq ,var ,temp))))))
bindings))
(eval-thunks ; Produce s-exp to evaluate thunks.
(cl-mapcar (lambda (binding)
(pcase-let ((`(,name ,_) binding))
`(funcall ,name)))
bindings))
(body (cl-gensym)))
`(let ,uninit-bindings
(let (,@assign-thunks (,body (lambda ()
,form
,@forms)))
,@eval-thunks
(funcall ,body)))))
Now the problem is that the macro works normally, but fails to work
after byte-compilation.
For example:
(funcall (lambda ()
(letrec2 ((sumtorial (lambda (n a)
(if (zerop n)
a
(funcall sumtorial (- n 1)
(+ n a))))))
(funcall sumtorial 100 0))))
=> 5050
But:
(funcall
(byte-compile
'(lambda ()
(letrec2 ((sumtorial (lambda (n a)
(if (zerop n)
a
(funcall sumtorial (- n 1)
(+ n a))))))
(funcall sumtorial 100 0)))))
gives the message "Symbol's function definition is void: nil".
Is this a bug, or a limitation I am unaware of?
Cheers,
Alex
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