I had published a shareware program called Envy (August of 2000) in the batchutl section here:

https://ftp.sunet.se/mirror/archive/ftp.sunet.se/pub/simteln...

(envy100.zip)

It was a program that provided 37 or so extension functions for batch scripts. Many of them that performed an expression evaluation left a result value in the environment of the parent process. Details and source code can be found in this old blog post:

https://www.mailsend-online.com/blog/envy.html

This really takes me back.