Some codes from “Essentials of Programming Languages, Third Edition,” MIT Press, 2008. http:https://www.eopl3.com/
can work with EoPL package of Racket v8.0 (or later)
# Mac
$ brew install --cask racket
# Ubuntu
$ sudo add-apt-repository ppa:plt/racket
$ sudo apt-get update
$ sudo apt-get install racketFYI: https://download.racket-lang.org/
Then, install package eopl.
$ raco pkg install eoplIt may take a litte longer.
Accept the program from stdin.
$ racket letrec.rkt
"letrec even(odd) = proc(x) if zero?(x) then 1 else (odd -(x,1))
in letrec odd(x) = if zero?(x) then 0 else ((even odd) -(x,1))
in (odd 13)"
#(struct:num-val 1)