To write code that performs decently in Emacs-Lisp, you have to work with buffer contents rather than substrings, and it is just another frustration, the primitives for working with buffer contents are low level and heavily stateful, you end up writing imperative code that looks a lot like pascal or whatever, while loops conditioned on regexp searches, tons of setq's, moving point and mark around etc. It isn't a convenient way of programmatically modifying text. The basic examples of doing search and replace described here:
http://ergoemacs.org/emacs/elisp_find_replace_text.html
give a flavour of this (and of not having keyword arguments, of libary functions relying on global variables, ...).