gistfile1.htm

<SCRIPT LANGUAGE='SCHEME'>(define (eval exp env)  (cond ((self-evaluating? exp) exp)  ((variable? exp) (lookup-variable-value exp env))  ((quoted? exp) (text-of-quotation exp))  ((assignment? exp) (eval-assignment exp env))  ((definition? exp) (eval-definition exp env))  ((if? exp) (eval-if exp env))  ((lambda? exp)  (make-procedure (lambda-parameters exp)  (lambda-body exp)  env))  ((begin? exp)   (eval-sequence (begin-actions exp) env))  ((cond? exp) (eval (cond->if exp) env))  ((application? exp)  (apply (eval (operator exp) env)  (list-of-values (operands exp) env)))  (else  (error "Common Lisp or Netscape Navigator 4.0+ Required" exp))))</SCRIPT>