#lang racket

(require racket/fixnum)

(provide explicate-control)

(define (explicate-control sexp)
  (match sexp
    [`(program ,info ,exp)
      `(program ,info ((start . ,(explicate-control-tail exp))))]))

; after a remove-complex-opera*, all expressions
; are compatible with C0
(define (explicate-control-tail exp)
  (match exp
    [(? fixnum?) `(return ,exp)]
    [(? symbol?) `(return ,exp)]
    [`(read) `(return ,exp)]
    [`(- ,e) `(return ,exp)]
    [`(+ ,e1 ,e2) `(return ,exp)]
    [`(let ([,var ,rexp]) ,body)
     (explicate-control-assign var rexp (explicate-control-tail body))]))

; stmt :=  (assign var exp)
; tail :=  (return exp) / (seq stmt tail)
(define (explicate-control-assign var exp c0-body) `()
  (match exp
     [`(let ([,v ,x]) ,b) (explicate-control-assign v x (explicate-control-assign var b c0-body))]
     [_ `(seq (assign ,var ,exp) ,c0-body)]))