A simple programming language? What is a simple toy research programming language that has simple denotational semantics (including numbers or reals) that is used often to demonstrate certain properties of programming languages, or other things?

I am looking to demonstrate an idea on a programming language, and I don't want it to be complex in syntax, and I also want it to have easy to understand denotational semantics.

I don't need a working implementation of the language. Just the syntax and denotational semantics for the syntax.

Thanks.
Joy comes to mind. It's a simple concatenative language that involves manipulations on a stack. It's essentially a reverse Polish notation for combinatory logic with quoting, developed by a professor of logic and programming so presumably it was taught in class. :)

I'm not 100% sure what qualifies as as denotational semantics, but, there is an algebra for it:

http://www.kevinalbrecht.com/code/joy-mirror/j04alg.html