A goroutine is a lightweight thread of execution.

```ada
with Ada.Text_IO;         use Ada.Text_IO;
with Ada.Calendar;        use Ada.Calendar;

procedure Goroutines is

   task type Goroutine is
      entry Start (From : String);
   end Goroutine;

   task body Goroutine is
   begin
      accept Start (From : String) do
         for I in 0 .. 2 loop
            Put_Line (From & " : " & Integer'Image (I));
         end loop;
      end Start;
   end Goroutine;

   function Sleep (Seconds : Duration) return Boolean is
   begin
      delay Seconds;
      return True;
   end Sleep;

   G1 : Goroutine;
   G2 : Goroutine;
   G3 : Goroutine;

begin
   -- Suppose we have a function call f(s). Here’s how we’d call that in the usual way, 
   -- running it synchronously.
   G1.Start ("direct");

   -- To invoke this function in a goroutine, use `go f(s)`. This new goroutine will 
   -- execute concurrently with the calling one.
   G2.Start ("goroutine");

   -- You can also start a goroutine for an anonymous function call.
   G3.Start ("going");

   -- Our two function calls are running asynchronously in separate goroutines now. 
   -- Wait for them to finish (for a more robust approach, use a `WaitGroup`).
   Sleep(1.0);
   Put_Line ("done");

end Goroutines;