The A-0 System, completed in 1952, was a set of instructions that translated symbols into machine languages. Subroutines were assigned call numbers and computers would find those on the magnetic tape and perform
the routines; mathematical functions.
Grace Hopper working on UNIVAC with coworkers. Image Courtesy of Computer History Museum.
"All I had to do was to write down a set of call numbers, let the computer find them on the tape, bring them over and do the additions. This was the first compiler."
Hopper’s compiler was met with resistance. The common opinion was that computers could only perform computations. Hopper was also told that computers were unable to be programmed in English, much less other languages,
such as French. It was not until two years later that Hopper’s compiler was accepted.
"I had a running compiler, and nobody would touch it because, they carefully told me, computers could only do arithmetic; they could not do programs. It was a selling job to get people to try it. I think that with any new idea, because people are allergic to change, you have to get out and sell the idea."