Re: Gnat bug or mistaken program?

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 2021-07-20 15:02, Richard Iswara wrote:
> I get this error on my program from the menu build => check semantic
> exponent must be of type Natural, found type "Standard.Float".
> 
> Should not 10 ** (log10 a + log10 b) = a*b?
> 
> This is my compiler build:
> 
> GNAT Studio Community 2020 (20200427) hosted on x86_64-pc-mingw32
> GNAT Community 2020 (20200429-93) targetting x86_64-pc-mingw32
> SPARK Community 2020 (20200429)
> 
> Here is the relevant part of program:
> 
> with Ada.Numerics.Elementary_Functions;
> use Ada.Numerics;


To make Ada.Numerics.Elementary_Functions."**" visible without 
qualification, you should also do "use Ada.Numerics.Elementary_Functions".

Otherwise the compiler will see only the predefined operator:

    function "**"(Left : Float; Right : Integer'Base) return Float

(see RM 4.5.6(9 and 10)) which explains why the compiler does not accept 
a floating-point value as the Right operand to "**".


> Logs : Float := 0.0;
> Multiples : Float;
    ...> Multiples := 10.0 ** Logs;  => this is where it fails


It fails because the compiler sees only the predefined "**" operator 
which has an integral right operand.