Must of course agree that you should start with the language basics, but, in answer to your question (in general terms):
  1. "y" is a list, a list of keys with values
  2. "left" and "right" are members (keys) of that list
  3. these keys have been assigned the value of 400

Note that $x(somthing) (from your title) is quite different than $x{somthing}.

In reply to Re: variable variations $x(somthing) by igelkott
in thread variable variations $x(somthing) by sandy268

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