Defining new commands in Lilypond (for koron symbol)

Question

I am trying to write a simple, minimalist script in LilyPond to create the koron symbol (used in Persian music).

I came up with the following solution, with satisfactory results, but my code is not well-organized:

koron = {
    \once\override Accidental.stencil = #ly:text-interface::print 
    \once\override Accidental.text = \markup {
        \overlay {
            \override #'(thickness . 1.5) {
                \draw-line #'(-.7 . .4)
                \draw-line #'(-.7 . -.4) 
                \translate #'(-.7 . -1.4)
                \draw-line #'(0 . 1.8)
            }
        }
    }
}

\markup {Mode of Dastgah} 

\score {
     {
        \omit Staff.TimeSignature
        \cadenzaOn
        \key c \major % not interested in automation of accidentals!
        \override Staff.KeySignature.stencil = #ly:text-interface::print
        \override Staff.KeySignature.text = \markup {
            \musicglyph #"accidentals.flat" % standard symbol added to key signature like this
            \overlay {
                \raise #1.5 {
                    \override #'(thickness . 1.5) {
                        \draw-line #'(-.7 . .4)
                        \draw-line #'(-.7 . -.4)
                        \translate #'(-.7 . -1.4)
                        \draw-line #'(0 . 1.8)
                    }
                }
            } % koron symbol added to key signature like this
        }
        \relative c' { 
            b!1 c \koron % replaces accidental of next note by koron
            deh e f g 
            a^\markup {
                \overlay {
                    \override #'(thickness . 1.5) {
                        \translate #'(1.5 . .7) {
                            \draw-line #'(-.7 . .4)
                            \draw-line #'(-.7 . -.4)
                            \translate #'(-.7 . -1.4)
                            \draw-line #'(0 . 1.8)
                        }
                    }
                } (var)
            } % koron in a text
            b 
            \bar "|."
        }
    }
}

My naive difficulty is with defining new commands. I wish LilyPond would accept a LaTeX tool like \newcommand, but apparently it does not. The variable "koron" in my code seems to be working fine, but when I try to define, for example,

koronsymboldraw = {
    \draw-line #'(-.7 . .4)
    \draw-line #'(-.7 . -.4)
    \translate #'(-.7 . -1.4)
    \draw-line #'(0 . 1.8)
}

to make things more modular, LilyPond gives me errors:

error: unknown escaped string: `\draw-line'
...

With the manual of LilyPond not being sufficiently helpful really, I hope I can get some thoughts here on how we can define efficient commands and functions in LilyPond, particularly for this code.

Answer 1

When you are defining a non-musical piece of script you often have to wrap it in a markup. Nesting markups is fine.

---

I don't know what version you are running, but this seems to work in version 2.19:

---

\version "2.19.48"

koronsymboldraw = \markup {
    \override #'(thickness . 1.5) {
        \overlay {
            \draw-line #'(-.7 . .4)
            \draw-line #'(-.7 . -.4)
            \translate #'(-.7 . -1.4)
            \draw-line #'(0 . 1.8)
        }
    }
}

koron = {
    \once\override Accidental.stencil = #ly:text-interface::print
    \once\override Accidental.text = \koronsymboldraw
}

\markup { Mode of Dastgah }

\score {
    {
        \omit Staff.TimeSignature
        \cadenzaOn
        \key c \major
        \override Staff.KeySignature.stencil = #ly:text-interface::print
        \override Staff.KeySignature.text = \markup {
            \musicglyph #"accidentals.flat"
                \raise #1.5 
                \koronsymboldraw 
        }
        \relative c' {
            b!1 c \koron
            deh e f g
            a^\markup { 
                \koronsymboldraw 
                \lower #0.5
                (var) 
            }
            b
            \bar "|."
        }
    }
}

Answer 2

In recent versions, persian.ly provides Persian accidentals as well as key signatures. I believe it is available since version 2.23.6.

Minimal example for dastgah-e shoor (in G):

\version "2.24.1"

\include "persian.ly"

\score {
  \header {
    piece = "Dastgah-e Shoor."
  }
  {
    \key g \shur
    \relative c' {
        bf1 c 
        d ef f g
        ak
        bf
        \bar "|."
    }
  }
}

The documentation about persian.ly provides some information (link), but I had to dig some specifics from the source code on GitHub: permalink.