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Zygo is a Lisp interpreter written in 100% Go
(github.com)
It would be weird if it were only 40% Go.
Lisp (historically LISP) is a family of programming languages with a long history and a distinctive, fully parenthesized prefix notation. Originally specified in 1958, Lisp is the second-oldest high-level programming language. Only Fortran is older, by one year.