[WISH] Squiggly lines on invalid argument type in function call?

[JakubKoralewski]

works-on-strings: function [
    arg1 [string!]
] [
    print arg1
]
works-on-strings 4

should visually indicate the following error

>> works-on-strings 4
*** Script Error: = does not allow integer! for its arg1 argument
*** Where: works-on-strings
*** Stack: works-on-strings

It does not for me at the moment: