On runtime, code can cause an error that halts the execution and potentially terminate the execution unexpectedly. Typically, this can occur on user input, when the user input is unexpected (for example, while the code expects a Decimal value and the user enters a value with letters). Exception handling enables you to deal with such situations and handle the thrown exception gracefully.

To handle an exception, use the try-catch construct on the code.

Also, you can decide that a particular expression should produce an exception. To throw an exception, use the error() function from the Standard Library.

Throwing Exceptions

The error() function throws an error with an error code. The error code is a String parameter of the construct.

error(<errorcode>)

Example:

error("InvalidISBNFormat")

If an error exception is not caught and handled, the execution terminates. The error can be caught and handled by a try-catch block.

Important: Error throwing functions are part of the Standard Library. Refer to the Standard Library Reference for further information.

Catching Exceptions

To catch and handle error exceptions produced by throw or by null function parameters which must not be null without interrupting the execution, use the try-catch statement block on the code which might cause an exception:

try <expression>
    catch <error_code>, ... -> <handle_expression_1>;
    handle_expression_2;
    ...
end

If the catch statement takes null, any error is caught.

Example:

try getCode()
  catch "Invalid ISBN format", "Invalid ISSN format" -> "Code value is not valid."
end

Example: Catching any error code

try getCode()
  catch null -> "Code value is not valid."
end

Note that the block returns an object, which you can cast as appropriate:

try val.toDecimal()
catch null -> "not decimal" as String

Built-in Errors

The Expression Language makes use of the errors with the following error codes: