If there is no second delimiter, the rules section is presumed to continue to the end of the program. Lines in the rules section that begin with white space and that appear before the first rule are copied to the beginning of the function yylex , immediately after the first brace. You might use this feature to declare local variables for yylex. Each rule specifies the pattern sought and the actions to take on finding it. The pattern specification must be entered at the beginning of a line.
Specification of Tokens. Regular expressions are an important notation for specifying lexeme patterns. While they cannot express all possible patterns, they are very effective in spec ifying those types of patterns that we actually need for tokens. In this section we shall study the formal notation for regular expressions, and in Section 3.
Transition diagram is a special kind of flowchart for language analysis. In transition diagram the boxes of flowchart are drawn as circle and called as states. States are connected by arrows called as edges. The label or weight on edge indicates the input character that can appear after that state.
A regular expression is a pattern that the regular expression engine attempts to match in input text. A pattern consists of one or more character literals, operators, or constructs. For a brief introduction, see. NET Regular Expressions. Each section in this quick reference lists a particular category of characters, operators, and constructs that you can use to define regular expressions.