test2.rkt

#lang racket

(struct fix-tag (tag contents))
(define fix-soh (string (integer->char 01)))

(define (compute-checksum tags)
  1)

;; creates tag string with SOH attached
(define (create-tag id contents)
  (string-append (string-join (list id contents) "=") fix-soh))

(define (create-msg tags)
  (let ([msg-partial (string-join tags fix-soh)]
        [msg-checksum (compute-checksum tags)])
   (string-append msg-partial fix-soh)))

(define test-msg (string-join '("8=FIX4.2." "10=341") fix-soh))
test-msg