Turning content into string

[lvjr]

In a comment in issue #2196, @EpicEricEE gave a function for turning content into string, but it failed when the content has some math function such as sin:

#let to-string(content) = {
  if content.has("text") {
    content.text
  } else if content.has("children") {
    content.children.map(to-string).join("")
  } else if content.has("body") {
    to-string(content.body)
  } else if content == [ ] {
    " "
  }
}

// succeed

#let c = [This _*cool*_ project]
#let s = to-string(c)
#type(s) // string type

// fail

#let c = [Hello $sin x$ World]
#let s = to-string(c)
#type(s) // content type

How to improve the to-string function, making it convert more math text to string?

[lvjr]

I found the cause of this problem: for sin function, op.text = [sin] which is not a string. And the following is an improved to-string function:

#let to-string(content) = {
  if content.has("text") {
    if type(content.text) == "string" {
      content.text
    } else {
      to-string(content.text)
    }
  } else if content.has("children") {
    content.children.map(to-string).join("")
  } else if content.has("body") {
    to-string(content.body)
  } else if content == [ ] {
    " "
  }
}