This and other RFCs are available on the web at http://dev.perl.org/rfc/ =head1 TITLE Make operators behave consistently in a list context =head1 VERSION Maintainer: Jeremy Howard <[EMAIL PROTECTED]> Date: 10 August 2000 Version: 1.00 Mailing List: [EMAIL PROTECTED] Number: 82 =head1 ABSTRACT It is proposed that in a list context, operators are applied component-wise to their arguments. Furthermore, it is proposed that this behaviour be extended to functions that do not provide a specific list context. =head1 DESCRIPTION Currently, operators applied to lists in a list context behave counter-intuitively: @b = (1,2,3); @c = (2,4,6); @d = @b * @c; # Returns (9) == scalar @b * scalar @c This RFC proposes that operators in a list context should be applied component-wise to the elements of their arguments: @d = @b * @c; # Returns (2,8,18) If the lists are not of equal length, the shorter lists should be treated as if they were padded with undefs at the right-hand end. However, this implicit padding should not cause these elements in the shorter lists to auto-vivify. Functions that do not return a list should be treated in the same way: @e = (-1,1,-3); @f = abs(@e); # Returns (1,1,3) =head1 IMPLEMENTATION These operators and functions should be evaluated lazily. For instance: @b = (1,2,3); @c = (2,4,6); @d = (-2,-4,-6); $sum = reduce ^_+^_, @b * @c + @d; should be evaluated as if it read: $sum = 0; $sum += $b[$_] * $c[$_] + $d[_] for (0..$#b-1)); That is, no temporary list is created, and only one loop is required. The proposal to handle functions is tricky, since there is currently no obvious way to see whether a function is going to return a list. Either we need some kind of more advanced prototyping (or other way of creating a signature), or we need to manually change functions provided with Perl to check for list context and Do The Right Thing. =head1 REFERENCES The Mathematica Navigator, Heikki Ruskeepää, Academic Press, ISBN 0-12-603640-3, p383. Expression Templates (C++ Implementation): http://extreme.indiana.edu/~tveldhui/papers/techniques/techniques01.html#l32 Implementation in Perl Data Language: http://pdl.perl.org
