Operators

• Parsing arithmetic-type expressions is not too uncommon

• A useful utility is an operator function:

     $expression = 
        operator($Term,   [lookfor(['OP', '+']), sub { $_[0] + $_[1] }],
                          [lookfor(['OP', '-']), sub { $_[0] - $_[1] }]);

     $term = 
        operator($Factor, [lookfor(['OP', '*']), sub { $_[0] * $_[1] }],
                          [lookfor(['OP', '/']), sub { $_[0] / $_[1] }]);

• This little bit of code writes a function that parses an input like 2 + 3 * 4 and calculates the result (14)

• For technical reasons, getting - and / to work requires some tricks

  • The complications are encapsulated inside of operator

  • We don't have to worry about them

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Copyright © 2007 M. J. Dominus