Re: common lisp vs elisp.

[Jean Louis <bugs@gnu.support>]

* Joost Kremers <joostkremers@fastmail.fm> [2021-06-20 09:46]:
> Second, IELM interacts with your Emacs session. If you set a variable or define
> a function in it, the variable or function is available throughout Emacs. SLIME
> interacts with a Common Lisp subprocess and whatever you do there has no effect
> on Emacs. So you can't define a function in SLIME and then call it from
> somewhere else in Emacs, nor can that function access Emacs' state.

Though it is possible to emulated or get some limited functionality by
calling external Lisp or other languages from Emacs Lisp:

(defun clisp-number-to-words (n &optional trim)
  "Returns the cardinal English number representation, for example if N is 4, it would return \"four\""
  (clisp (format "(format t \"~R\" %d)" n) trim))

Number of our ancestors in 50 generations (left to thinking):

(clisp-number-to-words (expt 2 50)) ⇒ "one quadrillion, one hundred and twenty-five trillion, eight hundred and ninety-nine billion, nine hundred and six million, eight hundred and forty-two thousand, six hundred and twenty-four
"

Or evaluating string with Perl programming language:

(defun perl (string)
  (if (rcd-which "perl")
      (if string
	  (rcd-command-output-from-input "perl" string)
	"")
    (rcd-warning-message "RCD ERROR: `perl' not found in $PATH")))

(perl "print 2 + 2") ⇒ "4"

(perl "print 2 + 2; print \"\n\"; print 10") ⇒ "4
10"

Or evaluating variable DATA as string, sending it to external Common
Lisp implementation CLISP and getting result from it:

(defun clisp (data &optional trim)
  (if (rcd-which "clisp")
      (let* ((value (if data
			(rcd-command-output-from-input "clisp" data "-q" "-norc" "-")
		      ""))
	     (value (if trim (string-trim value) value)))
	value)
    (rcd-warning-message "RCD ERROR: `clisp' not found in $PATH")))

(clisp "(princ (+ 2 2))") ⇒ "4
"

(clisp "(format t \"~R\" (expt 2 50))") ⇒ "one quadrillion, one
hundred and twenty-five trillion, eight hundred and ninety-nine
billion, nine hundred and six million, eight hundred and forty-two
thousand, six hundred and twenty-four
""

or with the macro that allows some easier Lisp writing and illusion of
direct evaluation:

(defmacro clisp-macro (&rest body)
  (declare (indent 1) (debug t))
  `(clisp (prin1-to-string (quote ,@body)) t))

(clisp-macro (format t "~R" (expt 2 50))) ⇒ "one quadrillion, one hundred and twenty-five trillion, eight hundred and ninety-nine billion, nine hundred and six million, eight hundred and forty-two thousand, six hundred and twenty-four"

Though I would like that this macro becomes able to evaluate any
number of forms. If somebody has a solutin, let me know.

(clisp-macro (princ "First form")) ⇒ "First form"
(clisp-macro (princ "First form") (princ "Second form")) -- not working

Of course this way it would work:

(clisp-macro (progn 
	      (princ "First form") (princ " Second form"))) ⇒ "First form Second form"

-- 
Jean

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