A try expression consists of a body, zero or more catch clauses, and an optional finally clause. The body is executed until it finishes or a Exception is thrown. A catch clause has a formal parameter declaration that specifies a Exception type. If a Exception is thrown out of the body before the body completes, the catch clauses are examined in order, and the first one whose variable type is compatible with the thrown value (as determined by isa) will be executed with the variable set to the caught value. The type of each catch clause variable must be a subtype of Exception and may not be a subtype of a previous catch clause variable.

The finally clause, if present, will always be executed after the body and any catch body, regardless of whether the body finished normally or not.

As of version 4.0 of the API, the try statement may produce a value based on its body and catch clause bodies but excluding the finally body. Just as with switch, a value will only be produced if the last statement of body and every catch-body either produces a value, throws an exception or returns. If the body executes without an exception being caught, then its final statement produces the value, otherwise the final statement of the catch clause body produces the value.

If a catch or finally clause itself throws a Exception, the current try expression is exited. Such a Exception may be caught by an outer nested try expression.

As of version 4.0 of the API, the return, break, and continue statements may be used to transfer control out of a try expression. They cannot, however, transfer control out of a finally block, as there may be an exception waiting to be rethrown as soon as the finally block finishes executing.

{value
    {let results:VBox = {VBox "computing ..."}}
    
    {results.add
        {try
            {results.add "step 1 ..."}
            {error "children playing"}
            "step 2 ..."
         catch th:Exception do 
            {format "warning: %s", th.value}               
         finally
            {results.add "done."}
        }
    }

    results
}