A UnreachableException is used as an exception that should never be thrown.

• ErrorCall and AssertionFailed means that the function is partially defined or missused (if some arguments shouldn't be passed).
• UnreachableException means that some expression, by definition, cannot be reached (for example, a default value when initializing an array, if each value is guaranteed to be overwritten before use).

IndexException replaces the less informative ArrayException and has more neutral names.

• UnacceptableExpansion - occurs if the desired range exceed the actual size
• UnexpectedRank - occurs when trying to convert a list into a generalized index of inappropriate dimension
• UndefinedValue - occurs if the value is undefined
• EmptyRange - occurs if range is empty
• IndexOverflow - occurs if index overflows range
• IndexUnderflow - occurs if index underflows range

Exception constructors are specified in the order of definition, this is the recommended check order.

If the error type may depend on the check order, it should be indicated in the documentation. For example: overflow is checked first, and then underflow. But if an overflow is detected, underflow may not be noticed.