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From: G <Dizzy@interact.net.au>
Subject: Simple Case Study in Types. Chords.
Date: 1999/11/16
Message-ID: <3831283B.20807F08@interact.net.au>#1/1
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Newsgroups: comp.lang.ada
Date: 1999-11-16T00:00:00+00:00
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  With the following code fragments, I am not
sure if I constructed the types in [Chord_Definition.ads]
such that they actually mean what I think they do.
(I have not worried about keys because that is unneccessary
and I am not planning on learning musical software design -
this is an exercise in type-casting and accessing records, for me).
  Please look through this brief code.  The [Chord_List]
contains thirteen elements to account for twelve semi-tones
and the octave (13th).  If I was to assign a [Major_Chord] variable
as an instance of  record [Chord_Fragment] I would need to define
the [Chord_List] array as containing the [one], [four] and [eight]
elements of type Twelve_Tone.
  Allowing that I have got my arrays and things in the right places
(even if they don't mean quite what I think they do), what small
ada code allows me to assign such a value to a variable
[Major_Chord] ?


--------------------------------
-- Chord_Definition.ads
-- a specification for a package
-- which defines chords
--------------

package Chord_Definition is

  type chord is abstract tagged null record;

  type Twelve_Tone is
  -- Thirteen because that allows the octave.
  (One, Two, Three, Four,
    Five, Six, Seven, Eight,
    Nine, Ten, Eleven, Twelve, Thirteen);

  type Chord_List is array (1..13) of Twelve_Tone;

  type Chord_Fragment is new Chord with
  record
    Current_Chord : Chord_List;
  end record;

  -- type Chord_Access is access Chord;
  -- (not sure about access types yet)

end Chord_Definition;
----------------------


------------------------------
-- Chord_Progression.adb
-- a simple procedure :
---------------------
with Chord_Definition;

procedure Chord_Progression is

   -- A sequence for compositional chord sequences.
  type Chord_Sequence is array
  (1..Chord_Definition.Chord_List'Last)
  of Chord_Definition.Chord_Fragment;

  -- I think I bodged that (?) with Chord_Sequence
  -- because I wanted to be able to define
  -- a sequence of variable chord_fragments.

  -- assign major_chord, minor_chord, etc. , but how ?
begin
  --- (...do stuff with chords...)
end Chord_Progression;

--------------------------------------------