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XS::APItest::KeywordRPN(3pm)          Perl Programmers Reference Guide          XS::APItest::KeywordRPN(3pm)



NAME
       XS::APItest::KeywordRPN - write arithmetic expressions in RPN

SYNOPSIS
               use XS::APItest::KeywordRPN qw(rpn calcrpn);

               $triangle = rpn($n $n 1 + * 2 /);

               calcrpn $triangle { $n $n 1 + * 2 / }

DESCRIPTION
       This module supplies plugged-in keywords, using the new mechanism in Perl 5.11.2, that allow
       arithmetic to be expressed in reverse Polish notation, in an otherwise Perl program.  This module has
       serious limitations and is not intended for real use: its purpose is only to test the keyword plugin
       mechanism.  For that purpose it is part of the Perl core source distribution, and is not meant to be
       installed.

   RPN expression syntax
       Tokens of an RPN expression may be separated by whitespace, but such separation is usually not
       required.  It is required only where unseparated tokens would look like a longer token.  For example,
       "12 34 +" can be written as "12 34+", but not as "1234 +".

       An RPN expression may be any of:

       1234
           A sequence of digits is an unsigned decimal literal number.

       $foo
           An alphanumeric name preceded by dollar sign refers to a Perl scalar variable.  Only variables
           declared with "my" or "state" are supported.  If the variable's value is not a native integer, it
           will be converted to an integer, by Perl's usual mechanisms, at the time it is evaluated.

       A B "+"
           Sum of A and B.

       A B "-"
           Difference of A and B, the result of subtracting B from A.

       A B "*"
           Product of A and B.

       A B "/"
           Quotient when A is divided by B, rounded towards zero.  Division by zero generates an exception.

       A B "%"
           Remainder when A is divided by B with the quotient rounded towards zero.  Division by zero
           generates an exception.

       Because the arithmetic operators all have fixed arity and are postfixed, there is no need for
       operator precedence, nor for a grouping operator to override precedence.  This is half of the point
       of RPN.

       An RPN expression can also be interpreted in another way, as a sequence of operations on a stack, one
       operation per token.  A literal or variable token pushes a value onto the stack.  A binary operator
       pulls two items off the stack, performs a calculation with them, and pushes the result back onto the
       stack.  The stack starts out empty, and at the end of the expression there must be exactly one value
       left on the stack.

OPERATORS
       These are the operators being added to the Perl language.

       rpn(EXPRESSION)
           This construct is a Perl expression.  EXPRESSION must be an RPN arithmetic expression, as
           described above.  The RPN expression is evaluated, and its value is returned as the value of the
           Perl expression.

       calcrpn VARIABLE { EXPRESSION }
           This construct is a complete Perl statement.  (No semicolon should follow the closing brace.)
           VARIABLE must be a Perl scalar "my" variable, and EXPRESSION must be an RPN arithmetic expression
           as described above.  The RPN expression is evaluated, and its value is assigned to the variable.

BUGS
       This module only performs arithmetic on native integers, and only a small subset of the arithmetic
       operations that Perl offers.  This is due to it being intended only for demonstration and test
       purposes.

       The RPN parser is liable to leak memory when a parse error occurs.  It doesn't leak on success,
       however.

SEE ALSO
       Devel::Declare, "PL_keyword_plugin" in perlapi

AUTHOR
       Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT
       Copyright (C) 2009 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE
       This module is free software; you can redistribute it and/or modify it under the same terms as Perl
       itself.



perl v5.12.5                                     2012-11-03                     XS::APItest::KeywordRPN(3pm)