Re: define-void-function

[Aaron Hill]

On 2020-05-07 9:42 pm, Freeman Gilmore wrote:
> On Thu, May 7, 2020 at 11:32 PM Aaron Hill <address@hidden> 
> wrote:
> > %%%%
> > \version "2.20.0"
> >
> > sum =
> > #(define-void-function
> >    (args)
> >    (number-list?)
> I know the the function uses a list for this because of the
> undetermined number of args as the lambda procedure did.   In
> (number-list?) how do you know what goes here, say it is not a number,
> like a list of similes?

You put whatever type predicate makes sense for the function.  The 
Notation Reference lists all of the predefined ones, whether they are 
primitives specified by R5RS (the Scheme standard that Guile follows) or 
defined by LilyPond itself.

But you can also define your own type predicates:

%%%%
\version "2.20.0"

#(define (flavor? x)
  (member x '(vanilla chocolate strawberry)))

cake =
#(define-void-function
  (flavor) (flavor?)
  (format #t "\n~a cake is delicious!" flavor))

\cake chocolate

#(define (flavor-list? x)
  (and (list? x)
       (every flavor? x)))

layeredCake =
#(define-void-function
  (flavors) (flavor-list?)
  (format #t "\n~{~a~^ and ~} cake is delicious!" flavors))

\layeredCake vanilla, strawberry
%%%%

====
GNU LilyPond 2.20.0
Processing `type-predicate.ly'
Parsing...
chocolate cake is delicious!
vanilla and strawberry cake is delicious!
Success: compilation successfully completed
====


> >    (format #t "\nargs: ~s, sum: ~s" args (apply + args)))
> I do not have a clue what this all means "(format #t "\nargs: ~s, sum:
> ~s" args"   Where can i find this information?

See the documentation on Formatted Output [1].  I have shared a PDF 
version of the Guile 1.8 docs here [2] that makes a handy companion to 
the LilyPond docs for offline use.  Also included is the R5RS reference.

[1]: 
https://www.gnu.org/software/guile/docs/docs-1.8/guile-ref/Formatted-Output.html#Formatted-Output
[2]: https://drive.google.com/open?id=1WQ6zhMRUxf6-zdw3Gcv0SuuUI311Bu90


> > \sum 2, 3, 5
> Tried this and {a \sum2,3,5 b} (note spacing) and it worked, which is
> what i was looking for.   But {a \sum 2, -3, 5 b} does not work?   How
> to fix this so it does?

Technically, when one says something like "2,3,5" in LilyPond, that is a 
key-list? as far as the parser's logic is concerned.  A "key" in this 
context refers to either an index (non-negative integer) or a symbol.

To support general numbers, you will need to use Scheme syntax:

%%%%
\sum #'(1 -2/3 4.5)
%%%%
====
args: (1 -2/3 4.5), sum: 4.83333333333333
====


-- Aaron Hill