type
  RangeEnumerator = record
  strict private
    FCurrent: integer;
    FStop: integer;
    FStep: integer;
    FPadding: integer;
  public
    class function Create(const Start, Stop, Step: integer): RangeEnumerator; static; inline;

    function MoveNext: boolean; inline;

    property Current: integer read FCurrent;
  end;

  RangeEnumerable = record
  strict private
    FEnumerator: RangeEnumerator;
  public
    class function Create(const Start, Stop, Step: integer): RangeEnumerable; static; inline;

    function GetEnumerator(): RangeEnumerator; inline;
  end;

function Range(const Stop: integer): RangeEnumerable; inline;
begin
  result := RangeEnumerable.Create(0, Stop, 1);
end;

{ RangeEnumerator }

class function RangeEnumerator.Create(const Start, Stop, Step: integer): RangeEnumerator;
begin
  result.FCurrent := Start;
  result.FStop := Stop;
  result.FStep := Step;
end;

function RangeEnumerator.MoveNext: boolean;
var
  next: integer;
begin
  next := FCurrent + FStep;

  result := (next < FStop);
  if (not result) then
    exit;

  FCurrent := next;
end;

{ RangeEnumerable }

class function RangeEnumerable.Create(const Start, Stop, Step: integer): RangeEnumerable;
begin
  result.FEnumerator := RangeEnumerator.Create(Start, Stop, Step);
end;

function RangeEnumerable.GetEnumerator: RangeEnumerator;
begin
  result := FEnumerator;
end;


procedure MatrixMultRange(const A, B: TMatrix; out R: TMatrix);
var
  i, j, k: integer;
  sum: double;
begin
  Assert(A.m = B.n);

  R := TMatrix.Create(A.n, B.m);

  for i in Range(A.n) do
  begin
    for j in Range(B.m) do
    begin
      sum := 0;
      for k in Range(A.m) do
      begin
        sum := sum + A[i, k] * B[k, j];
      end;
      R[i, j] := sum;
    end;
  end;
end;