Where does this esoteric Pascal operator come from?

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2024-10-17 18:30:04

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In the documentation for an implementation of Pascal for a Soviet computer, I've encountered a very weird language extension. I'll try to translate it:

When control reaches a branching operator, the Expression, which should be of a simple type, is evaluated, then control is passed to first Operator in the branch. [Forall j ls likely missing here. - LB] If the j-th operator of the branch has concluded, the branch is exited, and control is passed beyond end. During the execution of the j-th Operator, the back operator can be called.

During the execution of the back operator, the Expression is evaluated, and a search is performed for the closest dynamically preceding branch with a compatible value of its Expression. The values are compatible, when they are either equal, or one of them is equal to zero.