Hairy Control Structure
According to Hewitt, Peter Landin had introduced an even more powerful control structure using his "J" (for Jump) operator that could perform a non-local goto into the middle of a procedure invocation. In fact the "J" operator could jump back into the middle of a procedure invocation even after it had already returned. Drew McDermott and Gerald Sussman called Landin's concept the "Hairy Control Structure" and used it in the form of a nonlocal goto for the Conniver programming language. Scott Fahlman used Conniver in his planning system for robot construction tasks. This is related to what are now called re-invocable continuations.
Difficulties in communication were a root cause of the control structure difficulties.
Read more about this topic: Planner (programming Language)
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