---input---
#let song(
  header_display: (number, title, singer) => grid(
    inset: 0b10,
    grid.cell(fill: rgb(0xd0, 0xd0, 0xd0)),
    [
      #heading(title)
      #if singer != none {
        strong(singer) + "\n"
      } else {
        number
      }
    ],
  ),
  // comment
  doc,
)

---tokens---
'#let'        Keyword.Declaration
' '           Text.Whitespace
'song'        Name.Function
'('           Punctuation
'\n  '        Text.Whitespace
'header_display' Name.Variable
':'           Punctuation
' '           Text.Whitespace
'('           Punctuation
'number'      Name.Variable
','           Punctuation
' '           Text.Whitespace
'title'       Name.Variable
','           Punctuation
' '           Text.Whitespace
'singer'      Name.Variable
')'           Punctuation
' '           Text.Whitespace
'='           Operator
'>'           Operator
' '           Text.Whitespace
'grid'        Name.Function
'('           Punctuation
'\n    '      Text.Whitespace
'inset'       Name.Variable
':'           Punctuation
' '           Text.Whitespace
'0b10'        Literal.Number.Bin
','           Punctuation
'\n    '      Text.Whitespace
'grid'        Name.Variable
'.'           Punctuation
'cell'        Name.Function
'('           Punctuation
'fill'        Name.Variable
':'           Punctuation
' '           Text.Whitespace
'rgb'         Name.Function
'('           Punctuation
'0xd0'        Literal.Number.Hex
','           Punctuation
' '           Text.Whitespace
'0xd0'        Literal.Number.Hex
','           Punctuation
' '           Text.Whitespace
'0xd0'        Literal.Number.Hex
')'           Punctuation
')'           Punctuation
','           Punctuation
'\n    '      Text.Whitespace
'['           Punctuation
'\n'          Text.Whitespace

'      '      Text.Whitespace
'#heading'    Name.Function
'('           Punctuation
'title'       Name.Variable
')'           Punctuation
'\n'          Text.Whitespace

'      '      Text.Whitespace
'#if'         Keyword.Reserved
' '           Text.Whitespace
'singer'      Name.Variable
' '           Text.Whitespace
'!='          Operator
' '           Text.Whitespace
'none'        Keyword.Constant
' '           Text.Whitespace
'{'           Punctuation
'\n        '  Text.Whitespace
'strong'      Name.Function
'('           Punctuation
'singer'      Name.Variable
')'           Punctuation
' '           Text.Whitespace
'+'           Operator
' '           Text.Whitespace
'"\\n"'       Literal.String.Double
'\n      '    Text.Whitespace
'}'           Punctuation
' '           Text.Whitespace
'else'        Keyword.Reserved
' '           Text.Whitespace
'{'           Punctuation
'\n        '  Text.Whitespace
'number'      Name.Variable
'\n      '    Text.Whitespace
'}'           Punctuation
'\n'          Text.Whitespace

'    '        Text.Whitespace
']'           Punctuation
','           Punctuation
'\n  '        Text.Whitespace
')'           Punctuation
','           Punctuation
'\n  '        Text.Whitespace
'// comment'  Comment.Single
'\n  '        Text.Whitespace
'doc'         Name.Variable
','           Punctuation
'\n'          Text.Whitespace

')'           Punctuation
'\n'          Text.Whitespace