Besides their stack architecture, these processors were programed in variants of Algol. There was no assembly language support. They had virtual memory before IBM. These machines were truly ahead of their time.
I would also like to point out that the famous Dutch computer scientist Edsger Dijkstra was deeply involved with both Algol and Burroughs. He worked on the first Algol-60 compiler, and became a Burroughs Fellow in the early 1980s. He got a ACM Turing award, and shortly after his passing had another award named after him. Given your location in the Netherlands you should have some familiarity with his contributions to the computer science community.