Re: Lilypond structure / implicit - explicit / with statement

[David Wright]

On Mon 04 Apr 2016 at 12:46:37 (+0200), Bernard wrote:
> On 03-04-16 22:56, David Kastrup wrote:
> >Bernard <address@hidden> writes:
> >>That does help. I found out \with is a very special statement.
> >Not really.  \with can be part of other constructs, just like "else" can
> >be part of other constructs in many programming languages (including
> >Scheme).  It is not a "statement" at all.
> That does help a lot. Now I understand why there can not be anything
> before /with.
> >
> >>It influence what happens before the statement, it must be executed
> >>just after \new . That is the reason why my examples 4 and 5 did not
> >>work.
> >>And it influence what happens after the statement. If within the Staff
> >>not a additional Staff property can be set.
> >>
> >>No wonder it confuses me.
> >\with introduces "context modifications".  They are basic expressions in
> >that they can be stored in variables and passed to functions, but to
> >take effect, they need to be applied to an actually created context, and
> >there are various syntactic constructs for doing that.
> >
> >They "influence what happens after the statement" like any modification
> >to anything.  Their influence is restricted to contexts they are applied
> >to (possibly via layout or context definitions or wrapped into other
> >context modifications).
> >
> I still do not get it all. By the way, I am my self a Python
> programmer and object orientation in known to me.

[...]

Your example is incomprehensible to me as I've never used drum mode.
It's also large enough to obfuscate the problem.

Simplifying the code:

%%%%%%%%%%

mus = { e' f' g' a' }

\markup { with section }
\score { \new Staff \with { \override NoteHead.color = #red } \mus }

\markup { with section }
\score { \new Staff \with { \override NoteHead.color = #red } { e' f' g' a' } }

%% That worked. The \with { xxx } modified the music.
%% Then you took out the \with so the { xxx } now becomes the music.
%% (Music expressions can include context modifications as well as notes.)

%% Think of python's positional parameters and keyword parameters.
%% You start with ( keyword=argument, parm ) but you remove "keyword="
%% so you're left with ( argument, parm ) and "argument" becomes a
%% positional parameter instead.

%% In LilyPond, the "first positional parameter" is the music.
%% Most LilyPond elements consist of either   \element SINGLE-value
%% or   \element { SINGLE arbitrarily complicated expression }
%% and not   \element { argument } { parm }
%% So LilyPond does not allow a "second positional parameter".

\markup { without the use of the with section }
%% generate error
\score { \new Staff { \override NoteHead.color = #red } \mus }

\markup { without the use of the with section }
%% generate error
\score { \new Staff { \override NoteHead.color = #red } { e' f' g' a' } }

%% Your music now becomes treated as illegal source code because
%% it's syntactically a "second positional parameter".
%% However, if you move the music in with the "first positional parameter":

\markup { without the use of the with section }
\score { \new Staff { \override NoteHead.color = #red \mus } }

\markup { without the use of the with section }
\score { \new Staff { \override NoteHead.color = #red e' f' g' a' } }

\markup { without the use of the with section }
\score { \new Staff { e' f' \override NoteHead.color = #red g' a' } }

%%%%%%%%%%

If you really want a python example; when you
"skipped the   with   section" by deleting "\with"
what you did was like changing:

with fileinput.input(args, mode='rb') as theinput:
  for bytestring in theinput:
    nbytesscanned += len(bytestring)
    linenum += 1
    for k in bytestring:
      maxchar = max(maxchar, k)
      if k not in firsts: firsts[k] = linenum
      counts[k] = counts.setdefault(k,0) + 1

into:

fileinput.input(args, mode='rb') as theinput:
  for bytestring in theinput:
    nbytesscanned += len(bytestring)
    linenum += 1
    for k in bytestring:
      maxchar = max(maxchar, k)
      if k not in firsts: firsts[k] = linenum
      counts[k] = counts.setdefault(k,0) + 1

Python now has no idea what to do with the word "as".

Cheers,
David.