Am 27.06.2018 um 07:34 schrieb Freeman Gilmore:
Thanks Urs:
That worked. Problem was that I did not know that the
results would be displayed in the log window. The
tutorial I am using had some example like (+ 1 2 3) => and
I was expecting 6 in the same window on the next line when I
compiled.
This is what one refers to as a REPL (read-eval-print-loop),
which is what LilyPond's Scheme sandbox does.
This may be what you mean by " but no immediate expression
evaluation".
Yes. Frescobaldi deals with LilyPond *files*, not an
immediate expression evaluation.
Is => valid in guile?
No.
How would I display the results of (+ 1 2 3), at this point
of the tutorial it just says "(+ 1 2 3) => 6"?
When a tutorial writes "=>" it means: "You type in '(+ 1 2
3)', and the REPL will display '6'. So "=>" isn't a
syntactical construct but a typographical convention for "the
expression to the left evaluates to the datum on the right".
Tutorials usually want you to learn from this immediate
evaluation, and in Frescobaldi you have to always do that
extra step to display something. But in general it's worth
the effort, and I do that 90% of the time when I want to try
something out or learn more about Scheme.
For displaying values you can use #(display) or #(ly:message
"Some value: ~a" data) (to start with ...)
HTH
Urs
Thank you,
ƒg
Urs:
In you first example #(let...) what function does 'let'
preform? From your examples in "For displaying values you can
use #(display) or #(ly:message "Some value: ~a" data) (to start
with ...)", could you please give me examples of each? I need
this to study the tutorial using Frescobaldi.
OK, it probably wasn't such a good idea to use non-atomic examples.
Let me try to put it another way: what you have in Frescobaldi is
a LilyPond file. This file may include Scheme code, and LilyPond
even works if there is *only* Scheme code in the file and no score
is even generated. That way you can use LilyPond and Frescobaldi
as a tool to experiment with Scheme code.
When I started this post I was hoping that Scheme work with out score.
The way to include Scheme in LilyPond is the '#'. Whenever
LilyPond encounters this hash it will have the immediately
following expression evaluated by Scheme. Essentially the
expression is replaced by the resulting value.
This helped
a lot.
What you have already noticed is that this Scheme code is not
evaluated immediately (as is done on a REPL and what your tutorial
seems to assume), but only when compiling the LilyPond file.
One more thing to understand is the following: any Scheme
expression *evaluates to* something (like (+ 1 2 3) evaluates to
6). In a REPL this value is displayed but in LilyPond/Frescobaldi
it is not. If you write #(+ 1 2 3) in a LilyPond file it *will*
evaluate to 6 but it only has the effect of placing that value 6
in the LilyPond file, which will have no effect at all.
I figured this.
The additional effort you have to make is explicitly print any
value you want to inspect to the log window. Scheme provides some
functions for that purpose: display, print, pretty-print, and more.
#(define my-var 12)
#(display my-var)
will print '12' to the log window,
#(display (+ 1 2 3))
will print '6'
Now this helped because I was making it work with #(let...; above is
much simpler.
Note that display won't add a line break, so when you want to see
more than one value you'll want to add #(newline) expressions in
between.
Read that sum place.
A final remark: there are many Scheme implementations (or
dialects) around, with more or less subtle differences. When you
use LilyPond you have a very specific dialect available (the Guile
implementation in its version 1.8), plus when starting up LilyPond
a number of extra Guile modules and many LilyPond features are
automatically added. This means that when you follow a "Scheme
tutorial" not necessarily everything will match what you find in
LilyPond.
[And please allow me a plug: you may find rewarding to have a look
at https://scheme-book.ursliska.de
<https://scheme-book.ursliska.de>, which is far from complete but
aims at giving a slow-paced and detailed introduction specifically
from a LilyPond perspective]
This is what I have been looking for. Is there a PDF?
No, and currently my (Gitbook) build system is broken, so I can't even
upload updates. But the content is available in a bunch of Markdown
files, and I'd be ready to move on to a new system, possibly
Pandoc-based. If someone has a good suggestion for a tool/set-up to
create PDF documents and HTML sites from Markdown content (with LilyPond
syntax highlighting and inclusion of LilyPond scores) I'd be glad to
look into it.
Check your URL in this:
Last part of https://scheme-book.ursliska.de/scheme/expressions.html
"You can and should for now ignore everything you don't know about
that (we'll soon cover it in the chapter about variable binding
<https://scheme-book.ursliska.de/scheme/binding.html>) but simply
realize that within that “mess” we have inserted ..."
Well, like with Wiki systems you can enter links to pages that don't
exist yet. So that's simply part of the incompleteness of the "book",
and I can't do anything about it right now.
Best
Urs
Thank you, ƒg
Best
Urs
Thank you,
ƒg
_______________________________________________
lilypond-user mailing list
lilypond-user@gnu.org
https://lists.gnu.org/mailman/listinfo/lilypond-user
