*Usefulness* is almost certainly intensional. An *Image* can either be a beacon or a beckoning siren, with no way to distinguish from the type signature alone. That is, the use of an image may be maximally stateful.
Discussion was at a point like this one, parallel discussions about canalization and Sober's epiphenomenator, from which Glen's image of diffusion limited aggregation (DLA) emerged. I am very thankful for the ideas that blossomed in the process of stepping through those implementation details, those months back[⍼]. To write Sober's sort in the functional style is trivial, the type signature is obvious. In this sense, Sober's sort is prototypical of pure extensionality. However, to know the details of where one colored ball touches another of the same, intensionality creeps in and the purity of the code slips toward the stateful. With DLAs, something akin to stigmergy (though maybe not the same thing as stigmergy) appears. The particular form that the DLA takes is path dependent, that a local patch of the forming surface has access to capture a freely drifting particle is a function of the aggregates form, which is a function of the aggregates history. In a funny sense, one can claim, "stimulation of particles by the performance they have achieved"[⍾], with past "behavior" *canalizing* future "behavior". [⍼] https://github.com/jonzingale/Haskell/tree/67464a88f77d52954bdae617406d212a534bae44/blinky/diffusion_limited_aggregation [⍾] https://en.wikipedia.org/wiki/Stigmergy#:~:text=Stimulation%20of%20workers%20by%20the%20performance%20they%20have%20achieved .
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