One technique I use sometimes is to write another very small program to generate Perl code to create the constant hash, then paste the output of that program into your main program. Something like: 
print "my %opcode_map = (\n";
print "LD$_ => [".join(',',$_*3,$_*5,$_*7)."],\n"
  foreach (1,2,3);
print ")\n";

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Also, note that you should use parentheses not squiggly brackets to set up your hash, or else you may not get what you expect; use warnings will warn you about that.

In reply to Re: code that runs at module loading by sgifford
in thread code that runs at module loading by spurperl

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