[clean-list] observers in your plans?

[Carlos Aya]

Dear Clean Team,

Just curious if you have among the plans, implementation of so-called observer types, i.e. variables that do not add as counting occurences.

The problem with the following function ...

doIt :: *(a e) (Int -> e) -> *(a e) | Array a e
doIt arr f = {arr & [i] = f i \\ i <- [0.. (size arr)]}

... is that (size arr) counts as occurrence in the body of doIt, so arr cannot be unique. But as seen in the _SystemArray implementation, size only reads the size of the array which we know is fixed. So, truly its signature should be

size :: 0:arr -> Int

(I put 0: to indicate an "observed" parameter, out of my ignorance.. and based on Odersky paper...)

So, although doIt as idea doesn't conflict with update-in-place, it cannot be implemented in Clean.

What do you think?

Kind regards
Carlos



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