If you meant a specific library or different term, just let me know and I will rewrite the post for you. Remember Telnet?
Next time you need to debug an SMTP server or test a custom TCP service, skip nc (netcat) for an hour. Fire up a Lisp REPL, open a socket, and talk to the machine directly. You'll never look at curl the same way again. If you landed here searching for "Lisp CLOS" (Common Lisp Object System) or "Lisp TCO" (Tail Call Optimization), drop a comment below. I've got drafts on both. But if you really meant tlen as some obscure library... well, now you know how to roll your own. Happy hacking, parentheses and all.
;;; tlen.lisp - A minimalist Telnet echo server (require :usocket) ; A portable socket library (defun handle-client (stream) "Echo back whatever the client sends, but shout it in uppercase." (loop :for line = (read-line stream nil) :while line :do (write-line (string-upcase line) stream) (force-output stream))) lisp tlen
Note: "Tlen" is not a standard term in mainstream Lisp literature (Clojure, Common Lisp, Racket, etc.). It is most likely a typo or autocorrect error. Based on common search patterns, I have assumed you meant one of three things: (Common Lisp Object System), "TCO" (Tail Call Optimization), or "TELNET" (network protocols).
But as a learning tool ? Absolutely. Telnet is the "Hello World" of network protocols. And writing it in Lisp is like learning to cook by making bread from scratch—you understand every ingredient. If you meant a specific library or different
And Lisp? Lisp is the perfect knife for cutting through that stream. Modern APIs are obsessed with structure. GraphQL schemas, Protobuf definitions, OpenAPI specs. It's powerful, but it's heavy.
That's it. 15 lines of Lisp, and you have a protocol server. You might think: "A loop that reads and writes? Python can do that." Fire up a Lisp REPL, open a socket,
If you came of age in the modern cloud era (Post-2010), Telnet is that "insecure thing" you disable on routers. But for those of us who cut our teeth on BBSes, mainframes, or early Unix hacking, —a raw, text-based window into another machine.