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In computer programming, M-expressions (or meta-expressions) were intended to be the expressions used to write functions in the Lisp programming language. Data to be manipulated using M-expressions was to be written using S-expressions. M-expressions were used for the original theoretical language in early papers about Lisp, but the first working implementation of Lisp interpreted encodings of M-expressions as S-expressions, and M-expressions were never actually implemented. == Historical relation to S-expressions == An S-expression represents data made up of ''atoms'' and ''pairs''. As originally described, an atom was a symbol written in upper case, and a pair was delimited by parentheses. Shorthand list notation was described, though it originally separated list elements by commas rather than whitespace. For example (using spaces rather than commas): ((A B) (C D) (E F)) which represents a list of three elements, each of which is a list of two symbols. An M-expression could also use operator names, meta-variables, and argument lists. Operator names and meta-variable names were in lower case, to show that they were not symbols (i.e., not data). Argument lists were delimited by brackets, (CAR X)抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「M-expression」の詳細全文を読む スポンサード リンク
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