The expression problem has been known for quite some time [0].
Final tagless[1] is an fp approach and Object algebras[2] is an oop approach to solving this problem.
Setting aside the timelime, reading the various claims it seems like Eric Meijer, Anders Hejlsberg et al still had a hard time obfuscating the math to make patentable claims.
A naive read (on my part) of the claims looks like they wished to patent Object Algebras.