I used to work at an AI firm that used it. Large Lisp codebases are a minefield with near impossible security and debugging issues. I still love it as a programming language tho.
Sounds about like most large codebases. Languages can't save you from this, it seems, only discipline can.
Also so cool that you worked in AI! That’s my dream field :)
You have a function (defun my-val () "a string")
Referentially transparent, easy to reason about right? Wrong. Lisp strings are mutable, and everything is a reference. So if you do something like this
(replace (my-val) "b" :start1 0 :end1 1)
(my-val) => "b string"
I appreciate that CL doesn't force everything to be immutable, but it seems like at least strings would benefit from being treated as immutable values.
I thought I could do (string "a string") to prevent it, but that didn't work.
(concatenate 'string "a string") worked, though ...
[0] http://www.lispworks.com/documentation/HyperSpec/Body/03_aba...
edit: i adjusted my answer because i thought i was answering to parent