Static pipeline in Ada

main.adb

-- Usage example
with Ada.Text_IO; use Ada.Text_IO;
with Pipeline;

procedure Main is
   -- Pipeline functions
   procedure Step1 is
   begin
      Put("1");
   end Step1;

   procedure Step2 is
   begin
      Put("2");
   end Step2;

   procedure Step3 is
   begin
      Put("3");
   end Step3;

   -- Pipeline Steps using linked list representation (Step, Next_Pipeline_Step)
   procedure PStep3 is new Pipeline.Step(Step3);
   procedure PStep2 is new Pipeline.Step(Step2, PStep3);
   procedure PStep1 is new Pipeline.Step(Step1, PStep2);
begin
   -- Execute the pipeline
   PStep1;

   -- Make sure to compile with optimization options to unroll the pipeline & inline its steps.
   -- The result here would be :
   -- Step1;
   -- Step2;
   -- Step3;
   -- Otherwise, the stack increases in each step (PStep(N) calls PStep(N+1)), which is a behavior to avoid.
end Main;

pipeline.adb

package body Pipeline is
   procedure Step is
   begin
      F;
      Next_Step;
   end;

   procedure Null_Step is
   begin
      null;
   end Null_Step;
end Pipeline;

pipeline.ads

package Pipeline is
   -- Do nothing.
   procedure Null_Step;

   generic
      -- Function to be executed by the step.
      with procedure F;
      -- Next step to execute after F's, doing nothing by default.
      with procedure Next_Step is Null_Step;
   procedure Step;
end Pipeline;