in which the trapdoor is just after the statement labeled 10. (This is particularly surprising because the label doesn't appear to have anything to do with the flow of control at all!)
While sufficiently astonishing to the unsuspecting reader, this form of COME FROM statement isn't completely general. After all, control will eventually pass to the following statement. The implementation of the general form was left to Univac FORTRAN, ca. 1975 (though a roughly similar feature existed on the IBM 7040 ten years earlier). The statement AT 100 would perform a COME FROM 100. It was intended strictly as a debugging aid, with dire consequences promised to anyone so deranged as to use it in production code. More horrible things had already been perpetrated in production languages, however; doubters need only contemplate the ALTER verb in [COBOL].
COME FROM was supported under its own name for the first time 15 years later, in C-INTERCAL (see [INTERCAL], [retrocomputing]); knowledgeable observers are still reeling from the shock.
Node:
, Next:
, Previous: