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Date: Thu, 9 Aug 2018 05:44:12 -0700 (PDT)
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Subject: SI Units Checked and Unchecked
From: AdaMagica <christ-usch.grein@t-online.de>
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Xref: reader02.eternal-september.org comp.lang.ada:54102
Date: 2018-08-09T05:44:12-07:00
List-Id: <comp.lang.ada>

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.

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.

Have fun.
Christoph