Add on-page-greater-than, -less-than (on-the-fly)

Add on-page-greater-than, -less-than (on-the-fly)

Adds two new ready-made procedures for use with the
\on-the-fly conditional markup command.  They test whether a
page is greater than or less than a user-specified number.
Documentation for both of them is also part of this commit.

[pwm, 2014-03-18 03:07:23]

Using a different local branch did the trick.  -Paul

[Trevor Daniels, 2014-03-18 12:11:51]

LGTM

Trevor

[dak, 2017-06-09 13:36:53]

Ok, I've taken another look at something that should help with this amount of
fine-grained definitions.  Do you think that the following macro markup-when
would be fine-grained enough to forego these kind of definition?  I demonstrate
it for implementing on-page-greater-than but of course one may use it directly. 
Its first argument is of the same style as the #:properties keyword arg for
define-markup-command .

#(define-macro (markup-when properties cond)
  `(lambda (layout props arg)
    (let ,(map (lambda (p)
		(if (pair? p)
		 `(,(car p) (chain-assoc-get ',(car p) props ,@(cdr p)))
		 `(,p (chain-assoc-get ',p props))))
	   properties)
     (if ,cond (interpret-markup layout props arg)
      empty-stencil))))

#(define (on-page-greater-than nmbr)
  (markup-when ((page:page-number -1))
   (> page:page-number nmbr)))

\paper {
  #(set-paper-size "a7landscape")
  oddFooterMarkup = \markup \on-the-fly #(on-page-greater-than 3) "This is
long!"
}

\score {
  \repeat unfold 256 c'1
}

[pwm, 2017-06-10 19:36:30]

On 2017/06/09 13:36:53, dak wrote:
> Ok, I've taken another look at something that should help with this amount of
> fine-grained definitions.  

LGTM. Although I'm still new to understanding scheme macros, I 
think I understand the gist of what's going on.

> Do you think that the following macro markup-when
> would be fine-grained enough to forego these kind of definition?  

You mean so the user would use this markup-when macro to define their own
'on-page-greater-than' and/or 'on-page-less-than' (like you've shown), rather
than
adding them to LilyPond?  

If so, that seems fine to me.  They seem like fairly rare use cases. Would
make a good snippet for the LSR or docs, so it can be found and used when
needed.

> I demonstrate
> it for implementing on-page-greater-than but of course one may use it
directly.

Directly like this I assume? (Which works.)

\paper {
  #(set-paper-size "a7landscape")
  oddFooterMarkup = \markup \on-the-fly 
  #(markup-when ((page:page-number -1))
     (> page:page-number 3)) 
  "This is long!"
}

> Its first argument is of the same style as the #:properties keyword arg for
> define-markup-command .

That's a nice consistency.  I tried it out and the following works too:

#(define (onpage proc nmbr)
  (markup-when ((page:page-number -1))
   (proc page:page-number nmbr)))

\paper {
  #(set-paper-size "a7landscape")
  oddFooterMarkup = \markup \on-the-fly #(onpage > 3) "This is
long!"
}

-Paul

[dak, 2017-06-12 15:22:51]

On 2017/06/10 19:36:30, pwm wrote:
>
> That's a nice consistency.  I tried it out and the following works too:
> 
> #(define (onpage proc nmbr)
>   (markup-when ((page:page-number -1))
>    (proc page:page-number nmbr)))
> 
> \paper {
>   #(set-paper-size "a7landscape")
>   oddFooterMarkup = \markup \on-the-fly #(onpage > 3) "This is
> long!"
> }

Come to think of it, the only application would seem in connection with
\on-the-fly, so it should be possible to wrap the \on-the-fly invocation into
the macro as well.

I've put up issue 5145 for basically replacing \on-the-fly with $ when one
really wants to write this as \markup $(onpage > 3) "This is long!".

This requires an amended definition of markup-when adding a markup command
signature:

#(define-macro (markup-when properties . cond)
   `(let ((markfun
	   (lambda (layout props arg)
	     (if
	      (let ,(map (lambda (p)
			   (if (pair? p)
			       `(,(car p) (chain-assoc-get ',(car p) props ,@(cdr p)))
			       `(,p (chain-assoc-get ',p props))))
			 properties)
		,@cond)
	      (interpret-markup layout props arg)
	      empty-stencil))))
      (set! (markup-command-signature markfun)
	    (list markup?))
      markfun))

#(define (on-page-greater-than nmbr)
  (markup-when ((page:page-number -1))
   (> page:page-number nmbr)))

\paper {
  #(set-paper-size "a7landscape")
  oddFooterMarkup = \markup $(on-page-greater-than 3) "This is long!"
}

\score {
  \repeat unfold 256 c'1
}

I don't actually want to pursue this path as the preferred user interface: it
just seemed to me that it should work.