Re: Right of Optimize Eager Evaluation Away

[lutz@iks-jena.de (Lutz Donnerhacke)]

* Laurent Guerby wrote:
>It looks like to me that the Ada language more or less intend that
>functions shouldn't have side effects, since by example it allows the
>compiler to evaluate arguments and thus potentially calling functions
>in any order, or allows only "in" parameters for the programmer.
>
>The question is then, why stop at allowing any evaluation order and
>not just allow lazy evaluation as well?

You may provide a pragma to tell the compiler that this function is really a
pure functional function. Then it is allowed to optimize this way.

>The "pragma" I was mentionning could look like:
>pragma You_Can_Omit_Calls_To_This_If_The_Value_Is_Not_Needed (F);
>
>(obviously a better name is needed ;-). If an expression involves only

pragma Pure_Function ([Entity =>] function_LOCAL_NAME);
...

     Note: All functions in a Pure' package are automatically pure, and
     there is no need to use pragma Pure_Function' in this case.

     Note: If pragma Pure_Function' is applied to a renamed function,
     it applies to the underlying renamed function. This can be used to
     disambiguate cases of overloading where some but not all functions
     in a set of overloaded functions are to be designated as pure.