No, that's not why you can't re-cast (it shouldn't be).. It's just how MEL works as as scripting language I suppose. DIfferent languages, different quirks. Also nothing is actually saved into memory unless you execute the script. You can have dozens of lines and just highlight and execute one if you want. If you want to…
You didn't type it in correctly when you posted it here - a simple copy and paste into the script editor confirmed you had typos. I'd suggest you double check and try again
I'd go straight to python imo. If you get used to python and ever need to switch to MEL for whatever reason you won't have a problem adapting. Here's a good resource to get started with python. http://www.chadvernon.com/blog/resources/python-scripting-for-maya-artists/