Mocklisp is the extension language of Gosling Emacs

Gosling Emacs

Gosling Emacs was an Emacs implementation written in 1981 by James Gosling in C. Its extension language, Mocklisp, has a syntax that appears similar to Lisp, but Mocklisp does not have lists or any other structured datatypes...

. While resembling Lisp

Lisp programming language

Lisp is a family of computer programming languages with a long history and a distinctive, fully parenthesized syntax. Originally specified in 1958, Lisp is the second-oldest high-level programming language in widespread use today; only Fortran is older...

 in many ways, it is semantically quite different. Richard Stallman

Richard Stallman

Richard Matthew Stallman , often shortened to rms,"'Richard Stallman' is just my mundane name; you can call me 'rms'"|last= Stallman|first= Richard|date= N.D.|work=Richard Stallman's homepage...

 characterized it as a programming language that "looks syntactically like Lisp, but didn't have the data structures of Lisp. So programs were not data, and vital elements of Lisp were missing. Its data structures were strings, numbers and a few other specialized things." While it is true that many important language features were missing from Mocklisp, large elaborate programs were written in it, utilizing buffers and strings for complex data structures.

When Gosling Emacs

Gosling Emacs

Gosling Emacs was an Emacs implementation written in 1981 by James Gosling in C. Its extension language, Mocklisp, has a syntax that appears similar to Lisp, but Mocklisp does not have lists or any other structured datatypes...

became "Unipress Emacs", Mocklisp was renamed "MLisp".