Powershell function: overwrite variable error?

I'm trying to write a powershell function, pretty simple, but I seem to be bumping up against something that I haven't been able to find. I suspect it's just my lack of powershell/windows programming. When the below is ran I get "Cannot overwrite variable host because it is read only or constant"

My eventual goal is to create an FTP function that I can use in a loop to send a bunch of information to different hosts.

CODE:

function ftploop ($host,$user)
{
Write.Host "Host is: $host"
Wrote.Host "User is: $user"
}

ftploop hello john