In 1952, Grace completed her first compiler for Sperry, known as the A-0. The A-0 System was a set of instructions that could translate symbolic mathematical code into machine language. In producing A-0, she took all the subroutines she had been collecting over the years and put them on ta pe. Each routine was given a call number, so that it the machine could find it on the tape. "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," as described by Grace. After the A-0 s ystem, Grace and her staff produced versions A-1 and A-2, improvements over the older version. The A-2 compiler was the first compiler to be used extensively, paving the way to the development of programming languages.
Shortly after Grace completed the first compiler, she gave a talk on how it worked. She was met with the common opinion that a computer couldn't write its own programs. It took two years for the compiler to become accepted. "I had a running compiler," said Grace," and nobody would touch i t 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 with any new idea, because people are allergic to change, you have to get out and sell the idea."
Grace also originated the idea that computer programs could be written in English. She viewed letters as simply another kind of symbol that the computer could recognize and convert into machine code. Although dissuaded by the establishment, she followed her philosophy of " go ahead and do it. You can apologize later," and developed the B-0 compiler. This compiler came later to be known as FLOW-MATIC. FLOW-MATIC was aimed at business applications, such as calculating payroll and automatic billing. By the end of 1956, Hopper had UNIVAC I & II understanding twenty English-like st atements using FLOW-MATIC
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