From 61c40c765eea03bc1029b596a2d31ab70f26d82c Mon Sep 17 00:00:00 2001
From: David Kastrup <dak@gnu.org>
Date: Tue, 7 Jul 2015 21:44:59 +0200
Subject: [PATCH] Issue 4487/1: Implement partial function calls

A partial function call acts as a function where the start of the
argument list has already been supplied.  For example:

makeRed = \tweak color #red \etc

Then one can use this as

{ c' \makeRed d' e'-\makeRed -. }
---
 lily/include/lily-imports.hh   |  1 +
 lily/lily-imports.cc           |  1 +
 lily/lily-lexer.cc             |  1 +
 lily/parser.yy                 | 70 ++++++++++++++++++++++++++++++++++
 scm/ly-syntax-constructors.scm | 10 +++++
 5 files changed, 83 insertions(+)

diff --git a/lily/include/lily-imports.hh b/lily/include/lily-imports.hh
index 120ff11cb7..535b40bea4 100644
--- a/lily/include/lily-imports.hh
+++ b/lily/include/lily-imports.hh
@@ -119,6 +119,7 @@ namespace Syntax {
   extern Variable multi_measure_rest;
   extern Variable music_function;
   extern Variable music_function_call_error;
+  extern Variable partial_music_function;
   extern Variable property_operation;
   extern Variable repeat;
   extern Variable repetition_chord;
diff --git a/lily/lily-imports.cc b/lily/lily-imports.cc
index 6f16c0ebc0..2a8ecf9e84 100644
--- a/lily/lily-imports.cc
+++ b/lily/lily-imports.cc
@@ -112,6 +112,7 @@ namespace Syntax {
   Variable multi_measure_rest ("multi-measure-rest");
   Variable music_function ("music-function");
   Variable music_function_call_error ("music-function-call-error");
+  Variable partial_music_function ("partial-music-function");
   Variable property_operation ("property-operation");
   Variable repeat ("repeat");
   Variable repetition_chord ("repetition-chord");
diff --git a/lily/lily-lexer.cc b/lily/lily-lexer.cc
index 68b5578994..b6cbda7f97 100644
--- a/lily/lily-lexer.cc
+++ b/lily/lily-lexer.cc
@@ -57,6 +57,7 @@ static Keyword_ent the_key_tab[]
   {"description", DESCRIPTION},
   {"drummode", DRUMMODE},
   {"drums", DRUMS},
+  {"etc", ETC},
   {"figuremode", FIGUREMODE},
   {"figures", FIGURES},
   {"header", HEADER},
diff --git a/lily/parser.yy b/lily/parser.yy
index 25b7cd86c3..581791d256 100644
--- a/lily/parser.yy
+++ b/lily/parser.yy
@@ -265,6 +265,7 @@ int yylex (YYSTYPE *s, YYLTYPE *loc, Lily_parser *parser);
 %token DESCRIPTION "\\description"
 %token DRUMMODE "\\drummode"
 %token DRUMS "\\drums"
+%token ETC "\\etc"
 %token FIGUREMODE "\\figuremode"
 %token FIGURES "\\figures"
 %token HEADER "\\header"
@@ -693,6 +694,25 @@ identifier_init_nonumber:
         | embedded_scm
 	| full_markup_list
         | context_modification
+	| partial_function ETC
+	;
+
+partial_function:
+	MUSIC_FUNCTION function_arglist_partial
+	{
+		$$ = MAKE_SYNTAX (partial_music_function, @$,
+				  $1, $2);
+	}
+	| EVENT_FUNCTION function_arglist_partial
+	{
+		$$ = MAKE_SYNTAX (partial_music_function, @$,
+				  $1, $2);
+	}
+	| SCM_FUNCTION function_arglist_partial
+	{
+		$$ = MAKE_SYNTAX (partial_music_function, @$,
+				  $1, $2);
+	}
 	;
 
 context_def_spec_block:
@@ -2004,6 +2024,56 @@ function_arglist_skip_nonbackup:
 	}
 	;
 
+// Partial function arglists are returned just in their incomplete
+// state: when combined with the music function, the missing parts of
+// the signature can be reconstructed
+//
+// To serve as a partial arglist, the argument list must absolutely
+// _not_ be in "skipping optional arguments" mode since then there is
+// some backup token that has nowhere to go before \etc.
+//
+// So we can skim off an arbitrary number of arguments from the end of
+// the argument list.  The argument list remaining afterwards has to
+// be in not-skipping-optional-arguments mode.
+
+function_arglist_partial:
+	EXPECT_SCM function_arglist_optional
+	{
+		$$ = $2;
+	}
+	| EXPECT_SCM function_arglist_partial_optional
+	{
+		$$ = $2;
+	}
+	| EXPECT_OPTIONAL EXPECT_SCM function_arglist_nonbackup
+	{
+		$$ = $3;
+	}
+	| EXPECT_OPTIONAL EXPECT_SCM function_arglist_partial
+	{
+		$$ = $3;
+	}
+	;
+
+function_arglist_partial_optional:
+	EXPECT_SCM function_arglist_optional
+	{
+		$$ = $2;
+	}
+	| EXPECT_SCM function_arglist_partial_optional
+	{
+		$$ = $2;
+	}
+	| EXPECT_OPTIONAL EXPECT_SCM function_arglist_backup
+	{
+		$$ = $3;
+	}
+	| EXPECT_OPTIONAL EXPECT_SCM function_arglist_partial_optional
+	{
+		$$ = $3;
+	}
+	;
+
 function_arglist_common:
 	EXPECT_NO_MORE_ARGS {
 		$$ = SCM_EOL;
diff --git a/scm/ly-syntax-constructors.scm b/scm/ly-syntax-constructors.scm
index 04629bf655..b53e0cb34e 100644
--- a/scm/ly-syntax-constructors.scm
+++ b/scm/ly-syntax-constructors.scm
@@ -60,6 +60,16 @@
            n (type-name pred) (music->make-music arg))
    (*location*)))
 
+(define-public (partial-music-function fun args)
+  (let* ((sig (ly:music-function-signature fun))
+         (args (and (list args) (reverse! args))))
+    (and args
+         (ly:make-music-function
+          (cons (car sig) (list-tail (cdr sig) (length args)))
+          (lambda rest
+            (apply (ly:music-function-extract fun)
+                   (append args rest)))))))
+
 (define-public (void-music)
   (ly:set-origin! (make-music 'Music)))
 
-- 
2.39.2