BETA programming language, https://beta.cs.au.dk/

Chapter 3, Objects and Patterns

Oberon-2 type guards, which are basic but still have the same idea somehow, https://cseweb.ucsd.edu/~wgg/CSE131B/oberon2.htm

Modula-3 type case, https://www.cs.purdue.edu/homes/hosking/m3/reference/typecas...