Programmer defined arrays

[Georg Bauhaus <rm.dash-bauhaus@futureapps.de>]

IIUC, an array can be seen as a mapping

  (Index_Type[1], ..., Index_Type[n]) -> Component_Type

where n is finite.
Similarly, a function can be seen as a mapping (*)

  (Param_Type[1], ..., Param_Type[m]) -> Return_Type

We can write a function's body (or its expression in Ada 2012).
We cannot, however, express how the function's mapping is to be
translated into instructions to be executed by some processor.
That's the job of the compiler.

Suppose translating a function into its instructions is to
remain the job of the compiler. (Therefore, recursively, that of
the persons writing the compiler.)

In this light, why should we be given means to express how arrays
should be translated into instructions?

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(*) Both mappings are variable, since array components can be
assigned and since Ada functions are not pure, but that's an aside.