Re: SI Units Checked and Unchecked

["Dan'l Miller" <optikos@verizon.net>]

On Thursday, August 9, 2018 at 7:44:13 AM UTC-5, AdaMagica wrote:
> This is a complete rework using Ada 2012 predicates.
> 
> These packages provide a method to commpute with physical items in full generality under dimensional correctness checking. Dimensioned items are written in a natural style with the unit attached as a string.
> 
> The base type is private:
> 
>   type Item is private;
> 
> There are subtypes defined for all 7 base units defined in the SI system and many more:
> 
>   subtype Length is Item with Dynamic_Predicate => has_Dimension (Length, "m");
>   subtype Volume is Item with Dynamic_Predicate => has_Dimension (Volume, "m**3");
>   subtype Speed  is Item with Dynamic_Predicate => has_Dimension (Speed , "m/s");
>   subtype Force  is Item with Dynamic_Predicate => has_Dimension (Force , "N");
>   subtype Resistance is Item with Dynamic_Predicate => has_Dimension (Resistance, "Ohm");
> 
> Variables are defined like this:
> 
>   A: Acceleration := 5.0*"m/s**2";
>   V: Speed := 10.0*"km/h";
>   T: Time  :=  1.0*"min";
>   D: Length := V*T + 0.5*A*T**2;
> 
>   D := 1.0*"J";  will raise an exception.

Shouldn't the •entire• point of a units-of-measurement library (or feature of language) be compile-time errors, not run-time exceptions/errors.

> Units and prefixes are case sensitive (as defined in SI): "mS" is millisiemens, "Ms" is megasecond.
> 
> Dimensioned IO is also provided:
> 
>   V := 1.0*"m/s";          -- output as
>   Put (V);                 -- 1.0*m*s**(-1)
>   Put (V, Dim => "km/h");  -- 3.6*km/h
>   Put (V, Dim => "s");     -- will raise an exception
> 
> Download from here:
> http://www.christ-usch-grein.homepage.t-online.de/Ada/Dimension/SI.html
> 
> If you should use (even like) this method, please drop me a note with your findings.

I am an advocate of units-of-measure in programming.

I would be interested in a summary (or even better, an AI) that itemizes all the core-language obstacles in currently-standardized Ada to moving all the incompatible usages of units to be compile-time errors instead of raising exceptions.