From BorielWiki
Jump to: navigation, search

Compiler tools usually define patterns using regular expressions. Regular expressions are already provided by python importing the standard module re.

Blex will use Pattern objects to match it's pattern definition (a regular expression) against the input. When a pattern is recognized (matches the input), a Token instance will be generated, and the related pattern action will be called.

Pattern Class

The pattern class defined in Blex contains information related to the pattern definition. Pattern class properties are:

  • pattern: An string containing the regular expression definition that this pattern will match. E.g. '[A-Za-z]+'
  • re: It's a compiled regular expression python object (it's compiled for faster matching on succesive input tests) of the previous pattern property.
  • hook: It's the function that will be called just after this pattern has been matched. This function is referred as Token hook.
  • token: The the generated tokens will have when this pattern is matched. E.g. SEPARATOR or IDENTIFIER.