[racket] Are There More String Functions?

I just started getting my hands dirty with Racket on some utility
scripts. Overall, it's been a great experience. My scripts are
shorter, clearer and faster than the initial Python scripts I wrote
(but that could be because they're my second time around).

I did run into one constant obstacle while using Racket: the dearth of
convenience string functions. There are plenty of functions for
strings, but several functions that are present on other platforms
(e.g., Python, Ruby, Java, etc.) don't seem to be part of the Racket
standard library.

Some of the functions I couldn't find but would've been useful were
things like (in Racket-type naming):

string-starts-with?
string-ends-with?
string-index-of
string-replace
string-trim

I did a little google searching and most advice said to use the regex
library (which I did), but the code isn't as clear had I used
functions like the ones above.

Do these functions exist anywhere? Is there a great PLaneT package
that supplies these functions?

Thanks,
Cristian