Lenguajes de Programación

`interp` recursivo

#lang plai

(define-type RCFAE-Value
  [numV (n number?)]
  [closureV (param symbol?)
            (body RCFAE?)
            (env Env?)])

(define (boxed-RCFAE-Value? v)
  (and (box? v)
       (RCFAE-Value? (unbox v))))

(define-type Env
  [mtSub]
  [aSub (name symbol?)
        (value RCFAE-Value?)
        (env Env?)]
  [aRecSub (name symbol?)
           (value boxed-RCFAE-Value?)
           (env Env?)])

;; lookup : symbol env → RCFAE-Value
(define (lookup name env)
  (type-case Env env
    [ mtSub () (error ’ lookup ”no binding for identifier” )]
    [ aSub (bound-name bound-value rest-env)
      (if (symbol=? bound-name name)
          bound-value
          (lookup name rest-env))]
    [ aRecSub (bound-name boxed-bound-value rest-env)
      (if (symbol=? bound-name name)
(unbox boxed-bound-value)
(lookup name rest-env))]))

;; cyclically-bind-and-interp : symbol RCFAE env → env
(define (cyclically-bind-and-interp bound-id named-expr env)
  (local ([define value-holder (box (numV 1729))]
          [define new-env (aRecSub bound-id value-holder env)]
          [define named-expr-val (interp named-expr new-env)])
    (begin
      (set-box! value-holder named-expr-val)
      new-env)))

;; interp : RCFAE env → RCFAE-Value
(define (interp expr env)
  (type-case RCFAE expr
    [num (n) (numV n)]
    [add (l r) (num+ (interp l env) (interp r env))]
    [mult (l r) (num∗ (interp l env) (interp r env))]
    [if0 (test truth falsity)
      (if (num-zero? (interp test env))
          (interp truth env)
          (interp falsity env))]
    [id (v) (lookup v env)]
    [fun (bound-id bound-body)
      (closureV bound-id bound-body env)]
    [app (fun-expr arg-expr)
      (local ([define fun-val (interp fun-expr env)])
        (interp (closureV-body fun-val)
                (aSub (closureV-param fun-val)
                (interp arg-expr env)
                (closureV-env fun-val))))]
    [rec (bound-id named-expr bound-body)
      (interp bound-body
        (cyclically-bind-and-interp bound-id
            named-expr
            env))]))
interp recursivo

`interp` recursivo
