> >> 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, 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? 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 ..." Thank you, ƒg Best Urs Thank you, ƒg > > > > >
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