flex & bison
Chapter 1. Introducing Flex and Bison The earliest compilers back in the 1950s used utterly ad hoc techniques to analyze the syntax of the source code of programs they were compiling. During the 1960s, the field got a lot of academic attention, and by the early 1970s, syntax analysis was a well-understood field.
https://www.oreilly.com/library/view/flex-bison/9780596805418/ch01.html