There were several Burroughs APL systems. As I remember, the first was done by Larry Breed at Stanford for the Burroughs 220. A B5500 implementation described

There were several Burroughs APL systems. As I remember, the first was done by Larry Breed at Stanford for the Burroughs 220. A B5500 implementation described in the report cited here was done at the University of Washington by Gary Kildall and others. The B6500 implementation, an amazing multilevel factored interpreter system done by Jim Ryan is the creme de la creme of APL implementations.