operator
pattern => pattern-variable
The pattern variable assignment operator. You use => within a pattern to cause all or part of the pattern to be assigned to a pattern variable.
find white-space letter+ => found-word white-space output found-word
Note that you can only use => where a single and unambiguous pattern variable assignment can occur. The following code would be illegal, for instance, because the pattern variable assignment could take place more than once in the course of matching the pattern:
find white-space (letter => found-letter)+ white-space output found-letter