$ curl --location --request POST 'http://localhost:8000/hellos' \
→ --header 'Content-Type: application/json' \
→ --data-raw '(begin
→ (define (fac x)
→  (if (<= x 0) 1 (* x (fac (- x 1)))))
→ (fac 5))'
{"msg":120,"code":200}