common-lisp,eval , Format both an expression and its result without eval

Format both an expression and its result without eval


Tag: common-lisp,eval

I am trying to format an arbitrary expression, say (+ 2 3), and at the same time, its result, 5.

I have the following:

(defun expr-and-result (expr)
  (format t "~a returns ~a~%" expr (eval expr)))

CL-USER> (expr-and-result '(+ 2 3))
  (+ 2 3) returns 5

Though it's a simple matter by using eval, I'm curious if this effect can be accomplished without it (because I heard a lot that eval is to be avoided).

I understand that quoting the argument is necessary, because otherwise the given expression will be evaluated as the first step in calling expr-and-result, and only its result could be used inside expr-and-result. Therefore, any possible solution requires the input to be quoted, right?

I thought a bit about macros but I feel like it's the wrong approach to what I am looking for.

Edit: My intent was to construct a simple test-suite, such as:

  (mapcar #'expr-and-result
          '((= (my-remainder 7 3) 1)
            (= (my-remainder 7 3) 2)))

(= (MY-REMAINDER 7 3) 1) returns T
(= (MY-REMAINDER 7 3) 2) returns NIL

After reading Paulo's comment, it seems that eval is the shortest and cleanest solution for my purposes.


Here is a simple macro:

(defmacro exec-and-report (form)
  `(format t "~S returns ~S~%" ',form ,form))
(macroexpand '(exec-and-report (+ 1 2)))
(FORMAT T "~S returns ~S~%" '(+ 1 2) (+ 1 2)) ;
(exec-and-report (+ 1 2))
(+ 1 2) returns 3

PS. I second @Sylvester's suggestion not to reinvent the wheel


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