How to call Nim from Racket

fib.nim

proc fib(a: cint): cint {.exportc, dynlib.} =
  if a <= 2:
    result = 1
  else:
    result = fib(a - 1) + fib(a - 2)

fib.rkt

#lang racket/base
(require ffi/unsafe 
         ffi/unsafe/define)

(define-ffi-definer define-nim (ffi-lib "libfib"))
(define-nim fib (_fun _int -> _int))
(fib 23) ;; => 28657

shell

nim compile --app:lib -d:release fib.nim