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Código: waev2.rkt

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#lang plai

(define-type WAE
   [id (i symbol?)]
   [num (n number?)]
   [binop (f procedure?) (izq WAE?) (der WAE?)]
   [with (name symbol?) (named-expr WAE?) (body WAE?)])


(define (parse sexp)
   (match sexp
      [(? symbol?) (id sexp)]
      [(? number?) (num sexp)]
      [(list 'with (list id val) body) (with id (parse val) (parse body))]
      [(list op l r) (binop (elige op) (parse l) (parse r))]))

(define (elige sexp)
   (match sexp
      ['+ +]
      ['- -]
      ['* *]
      ['/ /]))

(define (subst expr sub-id val)
	(match expr
		[(id i) (if (symbol=? i sub-id) val expr)]
		[(num n) expr]
		[(binop f izq der) (binop f (subst izq sub-id val) (subst der sub-id val))]
		[(with bound-id named-expr body)
			(if (symbol=? bound-id sub-id)
				(with
					bound-id
					(subst named-expr sub-id val)
					body)
				(with
					bound-id
					(subst named-expr sub-id val)
					(subst body sub-id val)))]))

(define (interp expr)
	(error 'interp "Función no implementada"))