String Concatenation

I made a sandbox app to test simple pieces of code and I found out something interesting about string concatenation. I'm curious as to why it's implemented in this way.

The code:

sub RunUserInterface()

	mainScreen	= CreateObject("roPosterScreen")
	msgPort	= CreateObject("roMessagePort")
	mainScreen.SetMessagePort(msgPort)
	
	adjective = "funny"
	mainScreen.ShowMessage("this is a "+adjective+" test")          ' *** concatenation works correctly
	print "this is a "+adjective+" test"                            ' *** concatenation works correctly

	mainScreen.Show()

	while true
		msg = Wait(0, mainScreen.GetMessagePort())
		
		if type(msg) = "roPosterScreenEvent"
			if msg.isScreenClosed()
				exit while
			end if
		end if
	end while
	
	mainScreen.Close()

end sub

You can see that both the ShowMessage() function and the print statement uses a plus (+) sign to concatenation strings. I am able to change the code so that the print statement uses a semi-colon (;) instead, but if I also try that on the ShowMessage() function, I get a syntax error.

sub RunUserInterface()

	mainScreen	= CreateObject("roPosterScreen")
	msgPort	= CreateObject("roMessagePort")
	mainScreen.SetMessagePort(msgPort)
	
	adjective = "funny"
	mainScreen.ShowMessage("this is a ";adjective;" test")          ' *** concatenation does not work (syntax error)
	print "this is a ";adjective;" test"                            ' *** concatenation works correctly

	mainScreen.Show()

	while true
		msg = Wait(0, mainScreen.GetMessagePort())
		
		if type(msg) = "roPosterScreenEvent"
			if msg.isScreenClosed()
				exit while
			end if
		end if
	end while
	
	mainScreen.Close()

end sub