The expression problem has been known for quite some time [0].<p>Final tagless[1] is an fp approach and Object algebras[2] is an oop approach to solving this problem.<p>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.<p>[0] <a href="https://homepages.inf.ed.ac.uk/wadler/papers/expression/expression.txt" rel="nofollow">https://homepages.inf.ed.ac.uk/wadler/papers/expression/expr...</a><p>[1] <a href="https://okmij.org/ftp/tagless-final/" rel="nofollow">https://okmij.org/ftp/tagless-final/</a><p>[2] <a href="https://blog.acolyer.org/2015/11/13/scrap-your-boilerplate-with-object-algebras/" rel="nofollow">https://blog.acolyer.org/2015/11/13/scrap-your-boilerplate-w...</a>