A simple example of the kind of stuff you can do with constant generic parameters in the trunk version of Free Pascal

FreePascalConstGenerics.pas

program FreePascalConstGenerics;

// Using the Delphi-compatible syntax mode lets us leave out the
// `generic` and `specialize` keywords when defining our generic types.

{$mode Delphi}{$H+}{$J-}

type ICalc<const L: PtrInt; const R: PtrInt> = record
const
  Add = L + R;
  Sub = L - R;
  Mul = L * R;
  FDiv = L / R;
  IDiv = L div R;
  _Mod = L mod R;
  _And = L and R;
  _Or = L or R;
  _Shl = L shl R;
  _Shr = L shr R;
end;

type UCalc<const L: PtrUInt; const R: PtrUInt> = record
const
  Add = L + R;
  Sub = L - R;
  Mul = L * R;
  FDiv = L / R;
  IDiv = L div R;
  _Mod = L mod R;
  _And = L and R;
  _Or = L or R;
  _Shl = L shl R;
  _Shr = L shr R;
end;

type FCalc<const L: Double; const R: Double> = record
const
  Add = L + R;
  Sub = L - R;
  Mul = L * R;
  FDiv = L / R;
end;

type Calculation = FCalc<ICalc<1, 2>.Add, UCalc<3, 4>.Mul>;

begin
  WriteLn(Calculation.Add);
  WriteLn(Calculation.Sub);
  WriteLn(Calculation.Mul);
  WriteLn(Calculation.FDiv : 0 : 2);
end.