M-expression

In <a href="/facts/Computer_programming/QmSsFnu0">computer programming</a>, M-expressions (or meta-expressions) were an early proposed syntax for the <a href="/facts/Lisp_(programming_language)/xJHA3CrX">Lisp programming language</a>, inspired by contemporary languages such as <a href="/facts/Fortran/m1KqjcMU">Fortran</a> and <a href="/facts/ALGOL/wlFJGNEx">ALGOL</a>. The notation was never implemented into the language and, as such, it was never finalized.
M-expressions are a syntax for LISP code and provide <a href="/facts/Function_notation/CdReEKCh">function notation</a>, syntax for a cond form and for embedded literal data (via S-expressions) into programs. Thus M-Expressions used S-Expressions for literal data. The syntax for S-Expressions ("The Data Language") and M-Expressions ("The Meta Language") is defined on pages 8 and 9 of the Lisp 1.5 manual.
M-Expressions also had a corresponding S-Expression representation. Code was manually translated from M-Expressions to S-Expressions. The in M-expressions embedded literal data, then had to be quoted in S-Expressions.

M-expression open-in-new

M-expression