Find index of substring in Racket
<p>I read through <a href="http://docs.racket-lang.org/reference/strings.html" rel="nofollow">Racket's string library</a> but couldn't find a function equivalent to Java/JavaScript's <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#indexOf(java.lang.String,%20int)" rel="nofollow"><code>indexOf</code></a> method. That is, is there a function that returns the index of the first character of a substring within a larger string; preferably one that takes an optional start parameter. Something like:</p>

<pre><code>(string-index "foobar" "bar")
;;; returns 3
</code></pre>

<p>I'd be happy with something like lists' <a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._member%29%29" rel="nofollow"><code>member</code></a> function.</p>