Ad/2010-08-01 Concrete Syntax for a uml action Language for Foundational uml (Alf) Second Revised Submission
LANGUAGE DESCRIPTION 7Lexical Structure
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- Navigate this page:
- 7.1Line Terminators
- 7.2Input Elements and Tokens
- 7.3White Space
- 7.4Comments
- 7.4.1Lexical Comments
- 7.4.2Documentation Comments
LANGUAGE DESCRIPTION7Lexical StructureLexically, an Alf input text can be considered to be a sequence of input elements. This clause describes the structure of these input elements. After lexical analysis, the text can then be interpreted as a sequence of tokens that are then parsed according to the Alf syntax, as defined in Clauses 8 through 10. 7.1Line TerminatorsThe input text can be divided up into lines separated by line terminators. A line terminator may be a single character (such as a line feed) or a sequence of characters (such as a carriage return/line feed combination). This specification does not require any specific encoding for a line terminator, but any encoding used must be consistent throughout any specific input text. Any characters in the input text that are not a part of line terminators are referred to as input characters. Grammar LineTerminator = "\n" InputCharacter = any character other than LineTerminator 7.2Input Elements and TokensAn input element can be white space, a lexical comment or a token. Tokens include documentation comments, names, reserved words, literals, punctuation and operators. After whitespace and lexical comments are removed, the sequence of tokens is interpreted according to the Alf syntax. Grammar InputText = InputElement { InputElement } InputElement = WhiteSpace | LexicalComment | Token Token = DocumentationComment | Name | ReservedWord | Literal | Punctuation | Operator Cross References
7.3White SpaceA white space character is a space, tab, form feed or line terminator. Any contiguous sequence of white space characters can be used to separate tokens that would otherwise be considered to be part of a single token. It is otherwise ignored. There are two cases in which the line terminator is not syntactically considered to be white space. A list of annotations for a statement begins with the token “//@” and must end in a line terminator (see Subclause 9.2). And the heading for an in-line statement begins with the token “/*@” and must end in a line terminator (see Subclause 9.3). Grammar WhiteSpace = " " | "\t" | "\f" | LineTerminator Cross References
7.4CommentsComments are used to annotate other elements of the input text. They have no computable semantics, but simply provide information useful to a human reader of the text. There are three kinds of comments.
The first two kinds of comments are together known as lexical comments. 7.4.1Lexical CommentsLexical comments are not considered tokens. Therefore they are stripped from the input text and not parsed as part of the Alf syntax. The comment symbols and all comment text are ignored. However, a comment cannot occur within a name (see Subclause 7.5) or a string literal (see Subclause 7.7.4). Examples // This is an end-of-line comment and will be ignored. /* This is an in-line comment and will be ignored. */
LexicalComment = EndOfLineComment | InLineComment EndOfLineComment = "//" [ NotAt { InputCharacter } ] LineTerminator NotAt = InputCharacter but not "@" InLineComment
CommentText = { NotStar } [ StarCommentText ] StarCommentText= "*" [ NotStarNotSlash CommentText ] NotStar
NotStarNotAt = InputCharacter but not "*" or "@" | LineTerminator NotStarNotSlash = InputCharacter but not "*" or "/" | LineTerminator Cross References
7.4.2Documentation CommentsUnlike lexical comments, documentation comments are lexically processed as tokens and can therefore be included as syntactic elements. The intent is for documentation comments to be mapped to UML comment elements, containing the comment text, that are actually included as part of the target model. Note that line terminators are allowed within documentation comments. Examples /** This is documentation text to be included in the model. */ Grammar DocumentationComment = "/**" CommentText "*/" Cross References
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