Confusing "variable not in scope" error

[LightAndLight]

path : String
path = "example.com"

main : IO ()
main = println "https://$path?key=value"

Output:

$ ipso test.ipso
test.ipso:5:26: error: variable not in scope
  |
5 | main = println "https://$path?key=value"
  |                          ^

I felt confused when debugging a similar error. I looked at Ipso's error message, and thought to myself, "Why? path is in scope." After a few minutes, I realised I had forgotten that Ipso allows ? and ! in variable names, so the error was telling me that the variable path?key was not in scope, which is true. To fix the error, I need to write "https://${path}?key=value" so that the ? is treated literally.

If the caret in the error message was actually a span then I would have noticed this instantly:

$ ipso test.ipso
test.ipso:5:26: error: variable not in scope
  |
5 | main = println "https://$path?key=value"
  |                          ^~~~~~~~