これは簡単だなぁ。ほぼそのまま。 (defun if? (exp) (tagged-list? exp 'if)) (defun if-predicate (exp) (cadr exp)) (defun if-consequent (exp) (caddr exp)) (defun if-alternative (exp) (if (not (null (cdddr exp))) (cadddr exp) nil)) (defun eval…