Re: Building identifiers algorithmically

2015-03-22 Thread Richard Shann 
On Sun, 2015-03-22 at 08:01 +0100, David Kastrup wrote:
 Trevor Daniels t.dani...@treda.co.uk writes:
 
  Now while this works it seems rather clunky, so I'm wondering if there
  is a more elegant way of doing this.  Symbols look like they might
  help, but so far I've failed to make anything work.  I've also failed
  with macros, but that's likely because I don't understand them yet.
 
 When a function is evaluated, its arguments are read, evaluated, and the
 function is called with the unevaluated

I guess you meant evaluated here???

Richard


  arguments, and the result of
 that call is used.
 
 When a macro is evaluated, its arguments are read, the macro is called
 with the unevaluated arguments, and the result of that call is
 evaluated before use.
 
 It's just a matter of where the evaluation happens.  With a function, it
 is before the call, with a macro, it is after the call.  That's all
 there is to it.
 



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Re: Building identifiers algorithmically

2015-03-22 Thread David Kastrup 
Trevor Daniels t.dani...@treda.co.uk writes:

 Now while this works it seems rather clunky, so I'm wondering if there
 is a more elegant way of doing this.  Symbols look like they might
 help, but so far I've failed to make anything work.  I've also failed
 with macros, but that's likely because I don't understand them yet.

When a function is evaluated, its arguments are read, evaluated, and the
function is called with the unevaluated arguments, and the result of
that call is used.

When a macro is evaluated, its arguments are read, the macro is called
with the unevaluated arguments, and the result of that call is
evaluated before use.

It's just a matter of where the evaluation happens.  With a function, it
is before the call, with a macro, it is after the call.  That's all
there is to it.

-- 
David Kastrup

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Re: Building identifiers algorithmically

2015-03-22 Thread David Kastrup 
Richard Shann rich...@rshann.plus.com writes:

 On Sun, 2015-03-22 at 08:01 +0100, David Kastrup wrote:
 Trevor Daniels t.dani...@treda.co.uk writes:
 
  Now while this works it seems rather clunky, so I'm wondering if there
  is a more elegant way of doing this.  Symbols look like they might
  help, but so far I've failed to make anything work.  I've also failed
  with macros, but that's likely because I don't understand them yet.
 
 When a function is evaluated, its arguments are read, evaluated, and the
 function is called with the unevaluated

 I guess you meant evaluated here???

Whoever was sitting at my keyboard better would have meant evaluated.

  arguments, and the result of
 that call is used.
 
 When a macro is evaluated, its arguments are read, the macro is called
 with the unevaluated arguments, and the result of that call is
 evaluated before use.
 
 It's just a matter of where the evaluation happens.  With a function, it
 is before the call, with a macro, it is after the call.  That's all
 there is to it.

-- 
David Kastrup

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Building identifiers algorithmically

2015-03-21 Thread Trevor Daniels 
LilyPond Schemers,

I'm gradually getting the hang of Scheme, but I'd like some help with one 
frustrating issue.  I'd like to build an identifier from two strings and use it 
to reference a LilyPond variable.  

In other words, I have several Lily variables defined like this

SopranoMusic = \relative { ... }

and I'd like to reference them from Scheme code using the strings Soprano and 
Music.  The only way I've found is to build an alist of all of them using

#(set! index (assoc-set! index SopranoMusic SopranoMusic))

and then retrieve the music with

#(define music (assoc-ref index (string-append Soprano Music)))

(In my real-use case of course some of the strings are variables.)

Now while this works it seems rather clunky, so I'm wondering if there is a 
more elegant way of doing this.  Symbols look like they might help, but so far 
I've failed to make anything work.  I've also failed with macros, but that's 
likely because I don't understand them yet.

TIA, Trevor
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Re: Building identifiers algorithmically

2015-03-21 Thread Urs Liska 

Hi Trevor,

hey, that's what I just learned :-)

What you need is (ly:parser-lookup parser 'SopranoMusic) inside a music 
function.

Then create the 'SopranoMusic symbol from two strings and you're good to go.

\version 2.19.18

SopranoMusic = {
  c' d'
}


getMusic =
#(define-music-function (parser location label1 label2)
   (string? string?)
   (ly:parser-lookup parser
 (string-symbol
  (string-append label1 label2

\score {
  \new Staff \getMusic Soprano Music
}

HTH
Urs

Am 21.03.2015 um 23:29 schrieb Trevor Daniels:

LilyPond Schemers,

I'm gradually getting the hang of Scheme, but I'd like some help with one 
frustrating issue.  I'd like to build an identifier from two strings and use it 
to reference a LilyPond variable.

In other words, I have several Lily variables defined like this

SopranoMusic = \relative { ... }

and I'd like to reference them from Scheme code using the strings Soprano and 
Music.  The only way I've found is to build an alist of all of them using

#(set! index (assoc-set! index SopranoMusic SopranoMusic))

and then retrieve the music with

#(define music (assoc-ref index (string-append Soprano Music)))

(In my real-use case of course some of the strings are variables.)

Now while this works it seems rather clunky, so I'm wondering if there is a 
more elegant way of doing this.  Symbols look like they might help, but so far 
I've failed to make anything work.  I've also failed with macros, but that's 
likely because I don't understand them yet.

TIA, Trevor
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Re: Building identifiers algorithmically

2015-03-21 Thread Trevor Daniels 
Thanks Urs, that what I needed!

Trevor

- Original Message - 
From: Urs Liska u...@openlilylib.org
To: lilypond-devel@gnu.org
Sent: Saturday, March 21, 2015 10:44 PM
Subject: Re: Building identifiers algorithmically


 Hi Trevor,
 
 hey, that's what I just learned :-)
 
 What you need is (ly:parser-lookup parser 'SopranoMusic) inside a music 
 function.
 Then create the 'SopranoMusic symbol from two strings and you're good to go.
 
 \version 2.19.18
 
 SopranoMusic = {
   c' d'
 }
 
 
 getMusic =
 #(define-music-function (parser location label1 label2)
(string? string?)
(ly:parser-lookup parser
  (string-symbol
   (string-append label1 label2
 
 \score {
   \new Staff \getMusic Soprano Music
 }
 
 HTH
 Urs
 
 Am 21.03.2015 um 23:29 schrieb Trevor Daniels:
 LilyPond Schemers,

 I'm gradually getting the hang of Scheme, but I'd like some help with one 
 frustrating issue.  I'd like to build an identifier from two strings and use 
 it to reference a LilyPond variable.

 In other words, I have several Lily variables defined like this

 SopranoMusic = \relative { ... }

 and I'd like to reference them from Scheme code using the strings Soprano 
 and Music.  The only way I've found is to build an alist of all of them 
 using

 #(set! index (assoc-set! index SopranoMusic SopranoMusic))

 and then retrieve the music with

 #(define music (assoc-ref index (string-append Soprano Music)))

 (In my real-use case of course some of the strings are variables.)

 Now while this works it seems rather clunky, so I'm wondering if there is a 
 more elegant way of doing this.  Symbols look like they might help, but so 
 far I've failed to make anything work.  I've also failed with macros, but 
 that's likely because I don't understand them yet.

 TIA, Trevor
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