Name Errors/Dynamic/EmptySet

Synopsis Illegal operation on an empty set.

Function data RunTimeException = EmptyMap();

Usage import Exception;

Description Rascal provides many operations and functions on sets, see Rascal:Values/Set and Rascal:Prelude/Set. This error is generated when a function or operations cannot handle the empty set.

Remedies:

• Guard the function or operation with a test on the empty set (Rascal:isEmpty) and take alternative action in that case.
• Catch the EmptySet yourself, see Rascal:TryCatch.

Examples Import the Set library and introduce S with an empty set as value:

rascal>import Set;
ok
rascal>S = {};
set[void]: {}

Taking an element from an empty set gives an error:

rascal>getOneFrom(S);
|rascal://Set|(1712,454,<52,0>,<76,54>): EmptySet()
	at *** somewhere ***(|rascal://Set|(1712,454,<52,0>,<76,54>))
	at getOneFrom(|stdin:///|(11,1,<1,11>,<1,12>))

We can also catch the EmptySet error. First import the Rascal exceptions (which are also included in Prelude) and IO:

rascal>import Exception;
ok
rascal>import IO;
ok
rascal>try println(getOneFrom(S)); catch EmptySet(): println("Cannot apply getOneFrom to empty set");
Cannot apply getOneFrom to empty set
ok

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