Using a Scanner Generator

• The input consists of a list of pairs (pattern , action ).
  
  
• Whenever a pattern is recognized in the input, the action is performed.
• The patterns are regular expressions.
• Typically the action returns the token.
• The scanner generator uses this input to build a source file for the actual scanner.
• The longest possible input string is matched.
• If multiple input strings match, the action of the earlier is performed.
• In our project we will use the scanner generator JLex http://www.cs.princeton.edu/ appel/modern/java/JLex/