CODEWITHSUNDEEP
if-statementmacroslispcommon-lisp
Ivan1986
Ivan1986

Reputation: 19

Lisp Macro Multiple Tasks

I have a question about lisp macros. I want to check a condition and, if it's true, to run a few things, not only one. The same for the false way. Can anybody please help??

(defmacro test (condition (&rest then) (&rest else))
  `(if ,condition (progn ,@then) (progn ,@else)))

(test (= 4 3)
      (print "YES") (print "TRUE")
      (print "NO") (print "FALSE"))

Upvotes: 1

Views: 166

Answers (1)

sds
sds

Reputation: 60014

The usual way to test macros is to use macroexpand.

Your test case misses parens (lisp reader does not care about whitespace, such as line breaks and indentation):

(macroexpand '(test (= 4 3)
                    (print "YES") (print "TRUE")
                    (print "NO") (print "FALSE")))
  Error while parsing arguments to DEFMACRO TEST:
    too many elements in
      ((= 4 3) (PRINT "YES") (PRINT "TRUE") (PRINT "NO") (PRINT "FALSE"))
    to satisfy lambda list
      (CONDITION (&REST THEN) (&REST ELSE)):
    exactly 3 expected, but got 5

while

(macroexpand '(test (= 4 3)
                    ((print "YES") (print "TRUE"))
                    ((print "NO") (print "FALSE"))))
(IF (= 4 3)
    (PROGN (PRINT "YES") (PRINT "TRUE"))
    (PROGN (PRINT "NO") (PRINT "FALSE")))

Please note that CL has cond which is usually used when one needs multiple forms in if clauses.

Upvotes: 2

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