Re: question about transposing an interval of a 4th

[Mark Polesky]

> Graham Percival wrote:
> 1.  Look at the selected snippets for \transpose.  
> There's an example that's very close to what he 
> wants.

I disagree.

That example modifies the enharmonic spelling of 
notes in an already transposed section. We're looking 
for a function to transpose each note individually by 
the appropriate interval determined by its scale-
degree within a specfied tonality.

input: 
  \relative c' { \key c \major c4 d e f g a b c }

output:
  \relative c' { \key c \major g4 a b c d e f g }

> 2.  Look at
>   { \displayMusic { a ais d dis } }
> to get some info about how lilypond treats 
> pitches. The idea is to write a function that
> translates  "a ais" into "d dis". 

Not at all. The idea is to write a function that, 
given the key of C major, translates "a b" into 
"e f".

> 3.  Modify the existing example so that instead of 
> producing notes with few accidentals, it changes 
> the notename by the desired interval.

How is this helpful? This reminds me of the Monty 
Python skit on how to play the flute: "You blow 
there and you move your fingers up and down here." 
Besides, this doesn't account for the fact that 
different notes will need to be transposed by 
different intervals.

> If you cannot, or will not, describe what you 
> actually want, it's very difficult to help you.

He already has! He clearly stated that he wants to 
transpose music down a 4th, diatonically:
http://lists.gnu.org/archive/html/lilypond-user/2008-12/msg00557.html
If you don't know what diatonic means, look it up!

So far, the only post that offers promise is from 
John:
http://lists.gnu.org/archive/html/lilypond-user/2008-12/msg00591.html

but the programming is too tricky for me.

So John, if you get a chance to flesh this out, that 
would be awesome.

Thanks.
- Mark