Here is a snippet from an interview of B's creator, Ken Thompson in 1989, explaining this:
"MSM: Did you develop B?
Thompson: I did B.
MSM: As a subset of BCPL
Thompson: It wasn't a subset. It was almost exactly the same. It was a interpreter instead of a compiler. It had two passes. One went into intermediate language and which one was the interpreter of the intermediate language. Dennis wrote a compiler for B, that worked out of the intermediate language."
The B version for the Honeywell 6070 was compiled. B on the PDP-7 and -11 was interpreted. In fact I have a writeup on the threaded code for these two: http://squoze.net/B/
Here is a snippet from an interview of B's creator, Ken Thompson in 1989, explaining this:
"MSM: Did you develop B?
Thompson: I did B.
MSM: As a subset of BCPL
Thompson: It wasn't a subset. It was almost exactly the same. It was a interpreter instead of a compiler. It had two passes. One went into intermediate language and which one was the interpreter of the intermediate language. Dennis wrote a compiler for B, that worked out of the intermediate language."
~ https://www.princeton.edu/~hos/mike/transcripts/thompson.htm