String literals need to be quoted in perl. But: (from perlop)

       The => digraph is mostly just a synonym for the comma
       operator.  It's useful for documenting arguments that come
       in pairs.  As of release 5.001, it also forces any word to
       the left of it to be interpreted as a string.
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If you would have used use warnings (and also use strict), perl would have aborted with the following message:

    Bareword "value" not allowed while "strict subs" in use  
    at test.pl line 14.
    Execution of test.pl aborted due to compilation errors.
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Thus follows: use %a = (key => 'value');