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=head1 TITLE
Builtin: reduce
=head1 VERSION
Maintainer: Damian Conway <[EMAIL PROTECTED]>
Date: 4 August 2000
Version: 1
Mailing List: [EMAIL PROTECTED]
Number: 76
=head1 ABSTRACT
This RFC proposes a builtin C<reduce> function, modelled after Graham Barr's
C<reduce> subroutine from builtin.pm
=head1 DESCRIPTION
A new builtin -- C<reduce> -- is proposed.
This function would take an block, subroutine reference, or curried function
(hereafter referred to as I<the reduction subroutine>),
and call it repeatedly to reduce the remaining arguments
(hereafter, referred to as C<the list>).
If the reduction subroutine has a prototype, that prototype
determines how many items are reduced at a time. If the reduction subroutine
is a block or has no prototype, two items are reduced each time.
The first call to the reduction subroutine will be passed the first N
elements of the list, and subsequent calls will be passed the result of
the previous call and the next N-1 elements in the list, until no more
elements remain in the list. If fewer than N-1 elements remain on the
final call, all the remaining elemetns are passed.
If the original list has no elements, C<reduce> immediately returns C<undef>.
If the original list has a single element, that element is immediately returned
(without every calling the reduction subroutine).
Otherwise, the result of the final reduction call is the result returned
by C<reduce>.
If the reduction subroutine is ever terminated by a call to C<last>,
the enclosing C<reduce> immediately returns the last reduction value
(i.e. C<undef> on the first reduction call, $_[0] otherwise)
=head1 EXAMPLES
Summation:
$sum = reduce {$_[0]+$_[1]} 0, @numbers;
$sum = reduce sub{$_[0]+$_[1]}, 0, @numbers;
$sum = reduce ^_+^_, 0, @numbers;
Note that the first element of the list -- zero in this case, 1 in the next
example -- represents the default value if the list is empty.
Production:
$prod = reduce {$_[0]*$_[1]} 1, @numbers;
$prod = reduce sub{$_[0]*$_[1]}, 1, @numbers;
$prod = reduce ^_*^_, 1, @numbers;
Minimization:
$min = reduce ^x <= ^y ? ^x : ^y, @numbers
$min = reduce ^x le ^y ? ^x : ^y, @strings
Minimization to zero:
$min = reduce any(^x,^y)<0 && last || ^x<^y && ^x || ^y, @numbers
Collection:
@triples = @{ reduce sub($;$$$){ [@{shift},[@_] }, [], @singles };
Separation:
$sorted = reduce { push @{$_[0][$_[1]%2]}, $_[1]; $_[0] }
[[],[]],
@numbers;
=head1 IMPLEMENTATION
Extend Graham's builtin, I'd imagine.
=head1 REFERENCES
builtin.pm
