Compiler theory essays 2 (lexical analysis)

1, the main task

  From left to right scan the source, after pre-treatment, in accordance with the rules of recognition of each lexical correct word into a corresponding binary formula (class number, the code), submitted to the syntax analysis.

2, preconditioning

•   Disposal notes, spaces, tabs, line breaks
• After the end of the line statement, accompanied by a special character description
• To the identification code (reference numeral GOTO statement), reference numeral distinguished statement
• Outputs a source list for review

3, advanced search

For certain keywords without the protection of the language, we need to advance search

Note: The general high-level language does not require advanced search

4, the output format

Basic word (reserved word), flag word, constants, operators, delimiters

:( class of binary numbers, an inner code)

5, the scanner design

1. The written language lexical rules
2. Convert lexical rules to the state transition diagram
3. Each transition diagram of the initial state together, constitute this language recognition automata
4. Design scanner

• • The scanner as parsing a process required when parsing a word, is called a scanner.
  • Scanner from the initial state starting when identifying a word, it enters the final state , feeding of binary
  • NOTE: Alternatively matrix for transforming the state of FIG state, computer-implemented easily.

6, summed up

• Regular grammar, regular collection, formal type of relationship
  • Is a regular grammar production grammar is Chomsky 3 grammar, the grammar linear divided into left and right linear grammar
  • Regular set is the set of all meet the formal grammar.
  • The composition of the regular type, use a simple formula representation language
  • Relationship: regular grammar and style is formal rules, informal set is a collection. Regular regular grammar and style are equivalent, interchangeable
• Regular grammar -> Regular Expression
• Determination of NFA: Method subset
• DFA minimization:
• NFA containing e of determination of the arc
• Conversion regular grammar, regular type, automaton