2.7.15.4 Expedient Error Messages

Because there are so many ways to cause an invalid deconstruction, this message is the most common in practice and therefore the least informative. As a matter of convenience, avram takes the liberty of a slight departure from the virtual machine specification as written hitherto, and employs the following messages when invalid deconstructions occur respectively in the cases of recursion, transposition, and assignment.

• invalid recursion
• invalid transpose
• invalid assignment

That is, this section contradicts and supersedes what is stated at the end of Error Messages and implied by the operator properties P14, P16, and P42. It is also possible that user applications may modify the error messages by methods described in Computable Error Messages.

Whereas these three cases constitute an expedient variation on the semantics, there is another sense in which no possible implementation could conform faithfully to the specification. When an evaluation can not be carried out because of insufficient space on the host machine, one of the following error messages may be the result.

• memory overflow
• counter overflow

These messages are treated in the same way as those that are caused by programming errors, and propagate to the final result written to standard error without any specific consideration by the application developer. The latter occurs only in connection with the built in weight function (Weight). Other messages listed in Application Programming Errors are also of this ilk.

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