lilypond-0.0.40

[lilypond.git] / Documentation / language.pod

=head1 NAME

language.pod -- state of the art mudela-vapourware.

=head1 SYNOPSIS

(damn pod)

=head1 DESCRIPTION

here are some thoughts on the language. Most of the examples are in
pseudo current mudela.  Some stuff gratuitously taken from your mails.

=head1 NOTE

I dislike vapourware. That's why I oppose to concrete plans on how to
do input for features we don't know how to produce on paper 

=head1 AIM

A musical notation that is relatively easy to comprehend to both
programmers and non programmers. The final aim is to be able to
express what can be expressed in sheet music.

This document is intended to summarise the plans for mudela 2 (mudela
0 being mpp-input, and mudela-1 LilyPond input upto version 0.0.38).
Ideas for any further extensions (mudela 3, read total vapourware)
should be marked as such.


=over 5

=item *
play pieces

=item *
typeset the pieces

=back

further requirements:

=over 5

=item *
Possible to edit the layout without danger of changing the
original music. (fingerings, interpretation)

=item *
Simple music manipulations, such as transposing, creating a
score for individual instruments as well as for the conductor,
extracting short pieces from a longer one, glueing several shorter
pieces into a single score.

=back

Pieces could be:


=over 5

=item *
Mahlerian orchestral score

=item *
piano pieces

=item *
pop songs (lyrics + chords)

=item *
gregorian chant (?)

=item *
bach multivoice organ music.

=item *
short excerpts to be used in musicological publications.

=back

=head1 REQUIREMENTS

=head2 Parser output 

When I say LilyPond input, I mean the final output of the parsing
step, which should be roughly the same as it is now: hierarchically,
using pseudo syntax

        Score {
                Midi_def
                Paper_def
                Staff [multiple] {
                        Voices
                        Stafftype
                        (instrument)
                }
        }


Voice should stay the same:

        Voice {
                Voice_elements 
        }

and

        Voice_elements {
                requests
        }


=head2 Staffs

We definitely need the concept of staff in the parser output, because
it is fundamental to LilyPond.  I think the input language should
allow the user to do something like:

        melody = { c d e f g }

        %At this time I can't think of more than these stafftypes
        staff { gregorian music { melody } }
        staff { pianostaff music { melody } }
        staff { melodic music { melody } }
        staff { rhythmic music { melody } }
        staff { lyric music { melody } }        % silly, i admit.

The staff could also define what the instrument would be (both in
print and in MIDI)

Moreover, if music {} in score equals staff, then how do we do multiple
voices on one staff?

We might be able to do without the staff{} construct, but I doubt if
it will make things easier.

=head1 DECISIONS

[none, yet]


=head1 THOUGHTS

=head2 Typing

It is difficult to make mistakes with typing now because you have to
tell LilyPond what it is dealing with

        staff { identifier }

versus

        staff { music { identifier } }

I'm not sure on dropping this, I'm afraid it will make the language
less legible. Technically, dropping it is not very difficult (it will
introduce slight parser-source bloat)

What if the staff is extended to have some more blocks, all of which
can be declared? Like the score now:

        score {
                a_staff_id
                a_midi_id
                a_paper_id
                a_command_id
        }

This will only be readable if the Mudela-user rigidly uses hungarian,
which he/she won't.

=head2 Backslash

I like it. Let's keep it in the language if we need it, it's a
universally accepted escape sequence.

=head2 Braces

I like the idea of <> vs. {}. Not because I think it is more clear,
but I dislike the word "music", I can't seem to find the proper word
for what "music" currently does, so I'd like to flush it.

I would like to point that both <> and {} are indicating a
hierarchy. I think, we should continue to allow them to nest. I still
have no preference what to use for what.

=head2 Command syntax

Braces on commands are here now, because the {} are the only nesting
braces.  We need to avoid that, since the brace is overused as it
is. We don't like lisp that much. (the key is the only commands which
really needs {} now)

How about

        \bar "some args", "some more";

(note the ; ), which is a mix of perl and TeX.

Of course \key should take a \notename. In fact, I think we should
program the note intervals (which are now hardcoded for midi purposes)
To allow adaptation to other scales.

As simple fix, we might do key declarations:

        \keybes= \key { bes es }

        \key{\keybes}

[LOOSE]

We could be even more rabid, and use '\rab' as \bar terminator.

Just kidding of course...

[LOOSE THOUGHT]

We might drop this {} argument altogether, by merely enforcing
that each "statement" (music,score,staff,chord) takes a LIST as
argument, and use the {} to group lists. This is admittedly perl. This
is very sketchy.


=head2 Requests

I want to give the user some access to the internals. Technically,
walkers/registers will happily typeset voices which mix lyrics and
notes, which combine stem requests and lyricreqs. I want to have a

        \request { melodic name = 5, acc = -10
                rhythmic ball=4 dots 2, lyric = "foobar" }

type of syntax. This is the most flexible input format possible, since
any valid LilyPond input can be made. This strongly implies tying
mudela to LilyPond. That I don't mind, but it hampers
portability. Suppose some commercial systems want to read mudela
too.

=head2 Lexer modes

the $ and @ were quick hacks, which suck badly. Replacing it by a
mechanism that switches the lexer automatically would be better, but
it is still error prone, and it hurts uniformity. What I would like
best is unified syntax, but this seems impossible since lyrics could
clash with notenames. If possible it would simplify the parser, the
scanner, and the explanation of the language.

What about:

        bes c d e f     % notes
        'bes- sen sap   % some lyric syllables

We can make one of the ' ` " a lyric-indication, but then we would
have to change the octave indication, eg.

        _bes % lower
        ^bes % higher

or

        +bes % higher
        -bes % lower

And I am still not sure if it would be possible now, but I think this
is worthwile to investigate. Or we could replace @ by a
quote (take your pick) sign, which is a lot more intuitive. 

The big question remaining is: do we want to add any more modes than
lyric and note?


[LOOSE THOUGHT]

Even looser ideas: we can take a look at the perl wagon. It has numerous
inputmodes. What about:

        lyric << ENDLYRIC

        bes- sen- sap

        ENDLYRIC

        music << ENDMUSIC

        c d e f g

        ENDMUSIC


[LOOSE THOUGHT]

If we free up $ @ from their current meaning, $ and @ could be used to
signify other things.

=head2 Concrete solution to lyric vs. note

I think

        "lyric"

is a valid lyric too. This implies that any bare string is checked if
it is a note. Now it prints an error if not, but I could change it to
assume it is a STRING (and can be reduced to lyric). Heck! I could
implement this tonight. We'd lose one mode!  (after checking lexer
source) the only problem is preventing puctuation and the - and _ from
clashing with script symbols.


=head2 Command placement:

Mats is an arduous fan of having the commands inside music. I am
not. I see the Mudela music as something which can be plugged into
different staffs, transposed, translated in time, copied, quoted,
etc. Encouraging "inline" commands would be bad since they hinder this
reuse of mudela-isated music.

The way I figure it, the bad part is essentially counting
bars/wholes. Maybe we can get rid of it, by reinstalling the "mark"
commands.

I definitely want  to avoid complicated logic  ("Hey there is  another
bar request, should we merge this bar with another staff's", this kind
of "smartness" makes a  lot M$ software inconsistent) inside LilyPond,
by making the input unambiguous in this respect.

There is another complication: some symbols (bars) sometimes are
linked across staffs. I should first think of a way to do this in
LilyPond, before even considering a syntax.

[see also: filtering]

=head2 Volta

uhh?

=head2 Numbers

The syntax of /, * and : has to be settled, we have

        - notes (1, 2, 4, 8 etc), which also can take 1*2/3 to do plets.
        - meter 2*4
        - plet 2/3
        - multiple notes: 3*4
        - abbreviations (not implemented)  c4/4 or c4*4
        - measure grouping, {2*4 3*4}
        - skip 


=head2 Filtering

This is a idea of mine: we could filter some request types from
voices,

eg:

        \mel1 = \music { c-. d-. e-. f-. \meter {2*4} g-. a-. b.- c-. }

        \m1 = \filter { "script_req" \mel1 }
        \m2 = \filter { "command_req" \mel1 }
        \m3 = \filter { "melodic_req" \mel1 }
        \m3 = \filter { ("rhythmic_req") && (!"lyric_req") &&
                ("stem_req" || "beam_req") \mel1 }
                % syntax needs change. Clash with () slur?

        \mel2 = \music { c c g  g a a g2 }

        \combined = \merge { \m1, \mel2  }

This means m1 contains the scripts, of \mel, \m2 only the meter
command surrounded by (essentially) some skips, and \m3 the notes
without scripts or meters. This could be a solution to the "command in
music vs. command with skip".

Combined with merging of requests, this would be a powerful tool. In
this example \combined is a combination of melody mel2 and the accents
of \mel1.

This idea is for advanced users, but it would come in handy in urtext
editions:

        include "mozart-horn.ly"

        \m1 = \merge { \urmozart + \dennisbrain_interpretation }
        \m2 = \merge { \urmozart + \barrytuckwell_interpretation }


=head2 Proposed operators:

Just ideas:

        || && !         filter syntax 
        ++              concatenation of voices
        +               merging of voices


=head2 C++ OOP like input.

I don't see the big win of this.

        score sc1= melody;
        sc1.staff{\verse};
        sc1.staff{<\b1 \b2>}
        sc1.paper=mypaperdef;

We're not doing a programming language. In this syntax the parser has
to lookup what sc1 means, decide if it should copied shallow/deep,
decide if has a staff block, switch the mode after it finds that staff
takes music. May be I'm just ranting, but it looks hairy to
me. Remember that at this stage we're just filling structs.

In a distant future there might be a need for programming (are you
listening, Philip Glass?), but I think that would be something for
Mudela version 3. And I think using m4 (or something alike) would be
just as convenient.

It might clear things up, if JCN told us what is so special about this
syntax (without the C++ looks).

=head2 Transposition

Has to be done. How about:

        \transpose { \from c \to g \music { ... }} 

=head2 Quoting

Difficult. Hmm...

        \oboe = \music { ........................ }

        \oboefragment = \extract { \from 5*2 \to 6*2 \music { \oboe } }