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Wirth syntax notation (WSN) is a metasyntax, that is, a formal way to describe formal languages. Originally proposed by Niklaus Wirth in 1977 as an alternative to Backus–Naur Form (BNF). It has several advantages over BNF in that it contains an explicit iteration construct, and it avoids the use of an explicit symbol for the empty string (such as WSN has been used in several international standards, starting with ISO 10303-21. It was also used to define the syntax of EXPRESS, the data modelling language of STEP. == WSN defined in itself == SYNTAX = . PRODUCTION = IDENTIFIER "=" EXPRESSION "." . EXPRESSION = TERM . TERM = FACTOR . FACTOR = IDENTIFIER | LITERAL | "(EXPRESSION " )" | "(" EXPRESSION ")" | "" . IDENTIFIER = letter . LITERAL = """" character """" . The equals sign indicates a production. The element on the left is defined to be the combination of elements on the right. A production is terminated by a full stop (period). *Repetition is denoted by curly brackets, ''e.g.,'' *Optionality is expressed by square brackets, ''e.g.,'' *Parenthesis serve for groupings, ''e.g.,'' (a|b)c stands for ac | bc. We take these concepts for granted today, but they were novel and even controversial in 1977. Wirth later incorporated some of the concepts (with a different syntax and notation) into Extended Backus–Naur Form. Notice that letter and character are left undefined. This is because numeric characters (digits 0 through 9) may be included in both definitions or excluded from one, depending on the language being defined, ''e.g.'':digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" . upper-case = "A" | "B" | … | "Y" | "Z" . lower-case = "a" | "b" | … | "y" | "z" . letter = upper-case | lower-case . If character goes on to include digit and other printable ASCII characters, then it diverges even more from letter, which one can assume does not include the digit characters or any of the special (non-alphanumeric) characters.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「Wirth syntax notation」の詳細全文を読む スポンサード リンク
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