Unbound variable error when using defmacro in LISP -


i trying use macro 2 forms in lisp, evaluates both forms return result of form 2. below code using - 

(defmacro testmac (x body) (prog2 x body))

when executing macro following forms, works correctly , return 5 second form.

(testmac (- 10 6) (/ 10 2))

however when try execute macro following forms, return error.

(testmac (print a) (print b))

below error - 

debugger invoked on unbound-variable: variable b unbound. type debugger help, or (sb-ext:exit) exit sbcl. restarts (invokable number or possibly-abbreviated name): 0: [abort] exit debugger, returning top level. (sb-int:simple-eval-in-lexenv b #<null-lexenv>)

why getting error , how can use macro make work?

p.s. cannot use defun need use macro execute (testmac (print a) (print b))

i trying use macro 2 forms in lisp, evaluates both forms return result of form 2.

that's not idea - though might not precise wording. macro should not evaluate code - not without reason. macro transforms code. generated code decides evaluate.

(defmacro testmac (x body) (prog2 x body))  (testmac (- 10 6) (/ 10 2))

so x list (- 10 6) , body list (/ 10 2).

your macro returns second list.

cl-user 11 > (macroexpand-1 '(testmac (print a) (print b))) (print b)

the macro returns form (print b). gets executed.

cl-user 12 > (testmac (print a) (print b))  error: variable b unbound.

if b undefined error see.

there no magic going on.


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