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Testing an Icon table for the presence of a key

If you try to retrieve an item from a table using a particular key value, and nothing has ever been stored under that value, the result depends on how you created the table (see creating an Icon table).

• If you created the table with ``table(x)'', you will get the value x.
• If you used ``table()'' with no arguments to create the table, you will get a null value. You can use the ``/'' and ``\'' operators to test for this value (see how does the null value work in Icon?).

For example, if you have created the ``dayNumbers'' array (see storing items in an Icon table), this code would stop the program if there is no entry for the day with name ``today'':

    if  / dayNumbers[today]  then
      stop ( "Argh! There's no such day as ",
              today, "!" );