4.22.2 User-defined Exceptions

You can define your own exception types using the dclex statement:

dclex type

In this statement, type must be a valid MFL identifier, not used for another constant (see Constants). The dclex statement defines a new exception identified by the constant type and allocates a new exception number for it.

The type can subsequently be used in throw and catch statements, for example:

dclex myrange

number fact(number val)
  returns number
do
  if val < 0
    throw myrange "fact argument is out of range"
  fi
  …
done