In the design of programming languages, an erroneous program is one whose semantics are not well-defined, but where the language implementation is not obligated to signal an error either at compile or at execution time.
For example, in Ada: Defining a condition as "erroneous" means that the language implementation need not perform a potentially expensive check (e.g. that a global variable refers to the same object as a subroutine parameter) but may nonetheless depend on a condition being true in defining the semantics of the program.
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