Monks, I am writing a script that will perform a (specified on the command line) set of one or more operations on an input stream of rows of numbers (except the first column, which is the row ID). For example: if the input is
1 0 0 0 1 1 1 2 2
2 1 2 0 1 0 0 0 1
3 2 3 4 5 6 0 1 2
and the operation is "power" (2^x), then the output would be:
1 1 1 1 2 2 2 4 4
2 2 4 1 2 1 1 1 2
3 4 8 16 32 64 1 2 4
Operations can be "power", "log2", "loge", "log10", "round", etc. They can be specified multiple times too.
I would like to dynamically build a subroutine that called the specified subs in the right order.

Here is what I came up with; is there a better (more efficient, cuter, whatever) way to do this? (What am I thinking; obviously there are better ways to do this, after all, this is Perl!!) 

use Getopt::Long;
 
sub power { return exp( $_[0] ) }
sub log2  { return log( $_[0] )/log(2.0) }
sub loge  { return log( $_[0] ) }
sub log10 { return log( $_[0] )/log(10.0) }
sub round {
        my $n = shift;
        return int($n + 0.5) if ($n >= 0);
        return int($n - 0.5);
}
sub trunc { return int($_[0]) }
sub f1    { return sprintf "%.1f", $_[0] }
sub f2    { return sprintf "%.2f", $_[0] }
sub f3    { return sprintf "%.3f", $_[0] }
sub f4    { return sprintf "%.4f", $_[0] }
sub f5    { return sprintf "%.5f", $_[0] }
 
sub closure {
    my($sub, $arg) = @_;
    return sub { $sub->( &$arg ) }
}
 
my %opts = map { $_ => 1 }  qw( power log2 loge log10 round trunc f1 f
+2 f3 f4 f5 );
 
my $func = sub { return shift };
 
while (my $arg = pop(@ARGV) ) {
        $arg =~ s/^\-+//;
        if (defined ($opts{$arg})) {
                $func = closure( eval '\&' . $arg , $func );
        } else {
                print STDERR "Unknown arg: $arg\n";
        }
}
 
while (<STDIN> ) {
        chop;
        my @in = split;
        print shift(@in), " ";
        print join(" ", map { $func->($_) } @in), "\n";
}

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In reply to Dynamic function chains? by keymon

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