MLisp

"MLisp" is also another name for Mocklisp, a stripped-down version of Lisp used as an extension language in Gosling Emacs.

MLISP is a variant of Lisp with an Algol-like syntax based on M-Expressions, which were the function syntax in the original description of Lisp by John McCarthy. McCarthy's M-expressions were never implemented.

MLISP was first implemented for the IBM 360 by Horace Enea and then reimplemented for the PDP 10 by David Canfield Smith. This second implementation also supported a special kind of lambdas ("FEXPR"), which do not evaluate their arguments . As in Lisp-1 or Scheme, there was a single namespace for variables and functions.

While MLISP was just a preprocessor with an alternative, more reader-friendly syntax for Lisp, the descendant MLISP 2 introduced new concepts:

interactive interpretation of programs instead of compilation
extensibility with a syntax description language (see hygienic macros)
pattern matching
backtracking by the use of closures on a stack and indices for continuations

MLISP2 was called a transitional language by the authors. Larry Tesler improved the pattern matching system to implement a successor language called LISP70, which was only completed to a preliminary version. Though this path of LISP evolution is widely neglected, it resembles some features, later found in ML or Scheme.

M-LISP is a second branch — independent from the MLISP approach — and, as described by the author, essentially a hybrid of M-expression LISP and Scheme.

References

Enea, Horace (1968) MLISP CS-TR-68-92.pdf
Smith, David Canfield (1970) MLISP USERS' MANUAL Smith-MLISP-AIM-84.pdf (recommended first)
Smith, David Canfield and Enea, Horace J. (1973) MLISP 2 CS-TR-73-356.pdf (based on previous report)
Smith, David Canfield and Enea, Horace J. (1973) Backtracking in MLISP2: an efficient backtracking method for LISP 074.pdf
Tesler, Lawrence G., Smith, David Canfield and Enea, Horace J. (1973) The LISP70 pattern matching system 073.pdf
Muller, Robert (1989) MetaLISP: A Representation Independent Dialect of LISP with Reduction Semantics. PhD thesis
Muller, Robert (1990) Syntax macros in M-LISP: A representation independent dialect of LISP with reduction semantics
Muller, Robert (1990) Semantic Prototyping in M-LISP: A Representation Independent Dialect of LISP with Reduction Semantics
Muller, Robert (1991) M-LISP: Its Natural Semantics and Equational Logic
Muller, Robert (1992) M-LISP: A Representation-Independent Dialect of LISP with Reduction Semantics

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