Paul Rubin <no.email@nospam.invalid> writes:

> Does anyone know when lexical scope started appearing in Lisp?

You should find some information in

Steele, Guy L., and Richard P. Gabriel. "The evolution of Lisp."
History of programming languages---II. 1996. 233-330.
https://dl.acm.org/doi/pdf/10.1145/234286.1057818

For instance:

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When the IBM 370 came out, Lisp370 implementation began. [...]

Lisp370 supported both special binding and lexical binding, as well as
closures over both lexical and special variables, using a technique
similar to spaghetti stacks. (Page 31.)
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Scheme was one of the first languages to have taken seriously the
implications of lexical scoping (as opposed to local scoping, which
had been in use in Lisp compilers for almost a decade) and first-class
functions. (Page 23.)
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