Lilypond needs full support for arrow quarter-tone notation

[Joseph Wakeling]

> Not top-posting, guv.  Not me ...

%% In arrow quarter-tone notation, up- and down-arrows are
%% added to regular accidentals to indicate raising or lowering
%% by a quarter-tone.  This allows for two different accidentals
%% to indicate raising the pitch by a quarter-tone (natural-with-
%% up-arrow and sharp-with-down-arrow) and similarly for lowering
%% the pitch by a quarter-tone (natural-with-down-arrow and flat-
%% with-up-arrow.
%%
%% For a description of the notation, see K. Stone, "Music Notation
%% in the Twentieth Century", pp. 67-68 (scans not attached since
%% file-size is too big, but can be provided on request).
%%
%% Following the standard Dutch -is/-es sharp/flat notation, and
%% -ih/-eh for raising/lowering by 1/4-tone, as described in NR:
%%
http://lilypond.org/doc/v2.12/Documentation/user/lilypond/Writing-pitches#Note-names-in-other-languages
%%
%% Define:
%%            cih  =  c-natural-with-up-arrow = c + 1/4
%%            ciseh = c-sharp-with-down-arrow = c + 1/2 - 1/4
%%            ceh  =  c-natural-with-down-arrow = c - 1/4
%%            cesih = c-flat-with-up-arrow = c - 1/2 + 1/4

{
  cih2 ciseh2  %% these are the same pitches, but with different
               %% accidentals, both equal to c + 1/4-tone

  ceh2 cesih2  %% similarly, these are two different ways of writing
               %% the same pitch c - 1/4-tone
}

%% Lilypond's current method of internal pitch representation does not
%% permit two different accidentals for the same pitch in this way.
%% This is a general issue that affects implementation of many other
%% microtonal notations beyond arrow notation for quarter-tones.
%%
%% For background and further details see discussion on lilypond-devel:
%% http://www.mail-archive.com/address@hidden/msg30934.html