Modify HTTP::Host and HTTP::URI in an iRule

Thanks PK & DevBabu! You were both able to lead me to the solution. I just needed to add one additional piece to solve for website.com/folder instead of website.com/folder/

when HTTP_REQUEST {
    if { [HTTP::uri] ends_with "/folder"} {
         HTTP::redirect "http://folder.website.com"
    }
    elseif { [HTTP::uri] starts_with "/folder" && !([HTTP::uri] ends_with "/folder/")} {
        set path [HTTP::uri]
        set locate [string first "/" $path 1]
        set cleanpath [string range $path $locate end]
        HTTP::redirect "http://folder.website.com$cleanpath"
    } 
    elseif { [HTTP::uri] starts_with "/folder" && [HTTP::uri] ends_with "/folder/"} {
         HTTP::redirect "http://folder.website.com"
    }
}