Start1 by typing as much as code as you know will work

In my opinion an even better option is to start by writing a test for what you want to happen, then write the code to make that test pass. Repeat until code done.

Test Driven Development takes a little getting used to, but works very well in my experience. Advantages include:

1. You get pretty much 100% test coverage for free.
2. You always know when you have got a piece of code working.
3. You always know if a new piece of code breaks something.

So code a "caller" that uses that interface. In perl modules I tend to code this as a "main' program within the same file.

You can also do this sort of thing with Test::More and friends - and have the advantage of having something you can move to a test script later on. So instead of:

 package main;
 use strict;
 
 my $doit = doit->new();
 my @data = 1..10;
 print $doit->enumerate( \@data );
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do something like:

package main; 
use strict; 
use Test::More 'no_plan';

isa_ok my $doit = doit->new(), 'doit';
my @data = 1..10; 
is_deeply [$doit->enumerate( \@data )], [1..10], 'enumerate works';
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Then you don't have to think about whether what's being printed out is correct.