This works for me:

unless(@lexlist){@lexlist = sort keys %lexicon};

I think what you're missing is that you can't use "or" in that way, not what happens to @_.

UPDATE:

Here's my test to prove that @_ is not always evaluated to true:

&lex();

&lex(1,2,3);

sub lex{
  @lexlist = @_;
  if(@lexlist){
    print "I got the lexlist, here it is: @lexlist \n"
  }else {
    print "where's the list?\n";
  }
}
[download]

Which answers your question. --

($_='jjjuuusssttt annootthheer
     pppeeerrrlll haaaccckkeer')=~y/a-z//s;print;
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