Motif

Motif is a flexible way to manage patterns that generate unique results in cases where there are many sub-cases with additional sub-cases.

It lets you build simple decision trees without the need to create if statements. It makes the minimum number of comparisons necessary to generate a match.

The current version is v.2.0.0: This version has introduced breaking changes

Simple Example

Suppose you have the following mapping:

x:1      --> A
x:1, y:1 --> B
x:1, y:2 --> C

Then, motif gets the following results:

x:1      -> A
x:2      -> does not exist
x:1, y:1 -> B
x:1, y:2 -> C
x:2, y:2 -> does not exist
y:1      -> does not exist

A More Useful Example

Suppose we want to get the tax rate per country. For example, in Ireland the VAT is 23%, in UK 20%, etc. Moreover, each country has different tax classes. For details see here.

We define the tax for each case by creating unique patterns:

var
  taxFunc: TFunc<Double, Double>;
  motif: TMotif;

...
  
  motif:=TMotif.Create;
  taxFunc:=function (aRate: Double): Double
           begin
            // For illustration
            result:=aRate;
           end;

  motif.add<Double>('country: UK', function:double
                                   begin
                                     result:=taxFunc(0.19);
                                   end)
       .add<Double>('country: UK, type: food', function:double
                                   begin
                                     result:=taxFunc(0.00);
                                   end);

Finally, we retrieve the tax rate by, simply, calling this:

var
  list:TList<TMotifItem>;
begin
  ...
  list:=motif.find('country: UK');
  writeln(list[0].Value.AsExtended.tostring);

  motif.clear;
  list:=motif.find('country: UK, type: food'');
  writeln(list[0].Value.AsExtended.tostring);
  
  list.Free <-- Very important; this needs to be descroyed manually (but not to be created)
end;

Glob Matching

Motif understands glob matching. If the pattern is this:

b:1, x*y --> BC

Then, all the following calls will return BC

b:1, xAy
b:1, xhy
...

The pattern works the other way around. A request to b:* will also return a list with BC and any additional patterns registered with the prefix b:

Customisation

You can change the way values are stored in Motif. After Motif adds a value to the internal collection, it fires the OnAdd event.

Comparison with v.1.x.x

The Benchmark.Motif project generates 1,000,000 patterns and performs an addition, deletion, pattern finding ang glob finding

Test	v.1.2.0	v.2.0.0
add	12sec (254MB)	5.8sec (458MB)
remove	1.21sec (240MB)	445msec (320MB)
find	60sec (68.7MB)	1.36sec (68.7MB)
find glob	2min 30sec (68.7MB)	1min 3sec (68.7MB)

Inspiration

This project is inspired by patrun

License

This project is licensed under the Apache 2.0 license.

Contact

If you have spotted an error, have a suggestion, found any issues or a feature requests, please use the following channels. PRs are, also, welcome