sxmlinterp.scm

(use-modules (sxml transform))

(define (subst var val exp)
  (cond ((pair? exp)
         (cons (subst var val (car exp))
               (subst var val (cdr exp))))
        ((eqv? var exp) val)
        (else exp)))

(define *env*
  `((+ . ,(lambda (tag . vals) (apply + vals)))
    (* . ,(lambda (tag . vals) (apply + vals)))
    (let *macro* . ,(lambda (tag var val body)
                         (subst var val body)))
    (*text* . ,(lambda (tag val) val))))

(define (toy-eval exp)
  (pre-post-order exp *env*))

(toy-eval
 '(let x 10
    (+ x x)))