A few minutes ago, a node was posted as to why auto-decrement (--) wasn't magical. Since auto-increment is, this seems natural. It inspired me to throw together just such a function.
This is brute force, but it works. It's surprisingly difficult for something that looks so simple! So I'd love to see how this can be improved on—what language features could be brought to bear?
Perhaps reverse the string, then do a s///ge with inline code for a done flag as a zero-width lookahead, and the predchar feature in the replacement? Yaphy?
—John
use strict; use warnings; sub predchar # modify argument in place. # return true if no carry (done). { my $ord= ord($_[0]); my $nocarry; # define the ranges available my @ranges= ( [ord('0'),ord('9')], [ord('a'),ord('z')], [ord('A'),ord +('Z')] ); foreach my $range (@ranges) { my ($first,$last)= @$range; next unless $ord >= $first && $ord <= $last; # my range? if ($ord == $first) { $ord= $last } else { --$ord; $nocarry= 1; } } $_[0]= chr($ord); return $nocarry; } sub magic_decrement($) { my @chars= split ('', shift); for (my $loop= $#chars; $loop>=0; --$loop) { last if predchar ($chars[$loop]); } return join ('',@chars); } sub test { my $s= shift || $_; my $result= magic_decrement($s); print qq{--"$s" gives "$result"\n}; } while (<DATA>) { chomp; test; } __DATA__ 123 abc testbaA ignore punct.
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Replies are listed 'Best First'. | |
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Re: Magical Auto-Decrement
by Brovnik (Hermit) on Jul 04, 2001 at 21:34 UTC | |
by John M. Dlugosz (Monsignor) on Jul 04, 2001 at 21:40 UTC | |
Re: Magical Auto-Decrement
by Anonymous Monk on Dec 14, 2004 at 01:10 UTC | |
by Anonymous Monk on Dec 14, 2004 at 01:43 UTC |
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