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Apply reverse, tail, etc. on the result of 'map' and you get something of the same type. Types don't tell all.


What if you use a vector whole length is indexed by a Natural in the type signature? It would still allow permutations and such (like reverse), but not tail.

Using a dependent type system, it would actually be possible to statically ensure that map can only map, and do nothing else whatsoever, but it does become rather unwieldy.




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