ML Structure TutoriaL

(* IN *)
- structure test =
=  struct
=    val x = 2;
=  end;

(* OUT *)
structure test : sig val x : int end

(* IN *)
- structure test2 =
=  struct
=   structure test1 = test
=   val y = test1.x
=  end;

(* OUT *)
structure test2 :
  sig
   structure test1 : 
    val y : int
  end
	
(* IN *)
-test2.y;

(* OUT *)
val it = 2 : int

(* IN *)
-test2.test1.x;

(* OUT *)
val it = 2 : int

=========================

(* IN *)
- structure test = 
=   struct val x = 2
= end;
REPEATED DEFINITION FROM ABOVE


(* OUT *)
structure test : sig val x : int end

(* IN *)
-functor testFnc() =
=   struct  
=    val x = 2;
=   end;

(* OUT *)
functor testFnc : 

EACH INSTANCE OF A STRUCTURE CREATED VIA A PARTICULAR
FUNCTOR IS DISTINCT, WITH ITS OWN PLACE IN MEMORY.

(* IN *)
-structure test2 = testFnc();

(* OUT *)
structure test2 : sig val x : int end

(* IN *)
-test2.x;

(* OUT *)
val it = 2 : int

==================================

(* IN *)
- signature TEST = sig
=   val x : int
=  end;

(* OUT *)
signature TEST = sig val x : int end

RECALL FUNCTOR DEFINITION ABOVE
(* IN *)
- functor test2Fnc(test: TEST) =
=  struct
=    structure test1: TEST = test
=    val y = test1.x;
=  end;

(* OUT *)
functor test2Fnc : 

(* IN *)
- structure atest: TEST = testFnc();

(* OUT *)
structure atest : TEST

(* IN *)
- structure btest = test2Fnc(atest);

(* OUT *)
structure btest :
  sig
    structure test1 : 
    val y : int
  end

(* IN *)
- btest.y;

(* OUT *)
val it = 2 : int

(* IN *)
- signature TEST1 = 
=   sig   
=    val x1 : int
=   end;

(* OUT *)
signature TEST1 = sig val x1 : int end

(* IN *)
- signature TEST2 =    
=  sig
=   val x2 : int
=  end;

(* OUT *)
signature TEST2 = sig val x2 : int end

(* IN *)
- signature TEST3PIECES =
=  sig
=   structure test1 : TEST1
=   structure test2 : TEST2
=  end;

(* OUT *)
signature TEST3PIECES =
  sig
    structure test1 : sig val x1 : int end
    structure test2 : sig val x2 : int end
  end

(* IN *)
- functor test1Fnc() =
=   struct
=    val x1 = 1;
=   end;

(* OUT *)
functor test1Fnc : 

(* IN *)
- functor test2Fnc() =
=   struct
=    val x2  = 2;
=   end;

(* OUT *)
functor test2Fnc : 

(* IN *)
 - functor test3Fnc( pieces : TEST3PIECES ) =
 =   struct
 =     structure myTest1 = pieces.test1
 =     structure myTest2 = pieces.test2
 = 
 =     val x3 = myTest1.x1 + myTest2.x2;
 =   end;

(* OUT *)
 functor test3Fnc : 

 NOW WE USE THESE PIECES TO MAKE AN INSTANCE
 OF A STRUCTURE CALLED HERE test3

(* IN *)
 - structure test3Pieces : TEST3PIECES = 
 =   struct
 =    structure test1 : TEST1 = test1Fnc()
 =    structure test2 : TEST2 = test2Fnc()
 =   end;

(* OUT *)
structure test3Pieces : TEST3PIECES


(* IN *)
 - structure test3 = test3Fnc(test3Pieces);

(* OUT *)
structure test3 :
  sig
    structure myTest1 : 
    structure myTest2 : 
    val x3 : int
  end

(* IN *)
- test3.x3;

(* OUT *)
val it = 3 : int