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').
table(x)'', you will get the value x.
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 ``
`Storing items in an Icon table'),
this code would stop the program if there is no entry for the
day with name ``
if / dayNumbers[today] then stop ( "Argh! There's no such day as ", today, "!" );
John Shipman, email@example.com
Last updated: 1998/02/08 23:17:55 UT