Fixing hapless macros

Question

After some trial & error, I've managed to code a macro mashup to print the names & values of several variables (for debugging). It seems to work, but I'd like to see how to code this more "professionally"?

(defmacro prt1 (var) ;Print a single variable and its value. `(progn (princ (symbol-name ',var)) (princ " = ") (princ ,var) (terpri))) (defmacro prt (&rest vars) ;Print the values of a number of variable names. (eval `(append (list 'progn) (map 'list #'(lambda (x) (list 'prt1 x)) ',vars) (list (list 'terpri)) (list t)))) ;need to return t

Calling (prt A B C) then prints the current bindings--eg:

A = 1 B = 2 C = 3 T

Rainer Joswig · Accepted Answer · 2016-11-01 19:09:42Z

5

(defmacro prt1 (var) "Print a single variable and its value." `(format t "~a = ~a~%" ',var ,var)) (defmacro prt (&rest vars) "Print the values of variables." `(progn ,@(loop for var in vars collect `(prt1 ,var))))

answered Nov 1, 2016 at 19:09

Rainer Joswig

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1 Comment

davypough Over a year ago

Nice Rainer--but tried some minor modifications that just won't work!? (defmacro prt (&rest vars) "Print the values of variables." (progn (format t "~%") ,@(loop for var in vars collect (prt1 ,var)) (finish-output t) t)) Extra ~% to space output is ignored, and finish-output doesn't. The only change that does work is returning t! (I'm on SBCL.)

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