Organize computation around handling events emitted by input sources or changing state. A handler may update a model and then refresh derived views. The event source, subscription mechanism and handler logic are separate responsibilities; registering code without subscribing to its producer does not guarantee delivery.
A handler invoked again before a previous invocation has completed, for example through a synchronous notification caused by its own display update. A guarded refresh can suppress unintended recursive commits. Such a flag does not replace the need for a coherent state invariant and an explicit rule deciding which edit is authoritative.
A while loop tests a Boolean condition before each iteration and repeats its body while that condition is true. A loop invariant is established initially and preserved by every iteration; a loop variant decreases in a well-founded order to prove algorithm termination. The invariant together with the false exit guard establishes the postcondition.
// Target: computer-science.bigb
