Exceptions

Exceptions

Limbo supports the throwing, catching, and custom definition of exceptions.

The example in this section is a derivative of the exceptions summary in the Limbo Addendum.

Source

exceptions.b:17,26

This section calculates numbers within the fibonacci sequence to a given interval. In this case, the first 5 numbers are calculated within the sequence.

Note the call to the raise keyword after the fibonacci calculations have completed, but before the program exits.

exceptions.b:31,47

The fibonacci() function attempts to perform a fib() call and, if an exception e is thrown, attempts to handle the exception in a manner depending on the exception type.

Note that the attempted operation is wrapped in a { ... } block.

exceptions.b:49,63

The raises clause allows for warnings to be generated for un-caught exception potential within a program. Note that these exception types can be user-defined.

The FIB exception type is defined at: exceptions.b:12

Demo

; limbo exceptions.b
; exceptions
F(0) = 1
F(1) = 1
F(2) = 2
F(3) = 3
F(4) = 5
sh: 798 "Exceptions":going down!
; 

Exercises

• Try removing the raise for "going down!".
• Remove the i < 5 portion of the for loop, how many values are printed and why?
• Try removing the exception-catching block from around calls to fib(), do you get warnings?
• Try changing the raise type within fib(), does fibonacci() handle the exception e differently?