BLAH! help with calling class functions as function variables

I have a class called "table" and one of the functions in it is called "a" I have is set up like this

a($row, $title, $buttons, $body, $foot)

I also have a class called forms that has a function called userdetails that has no function vaiables

So I'm trying to get the $body variable of $tables->a() to equal $forms->userdetails()

so i do this

$table->a("left","Main Menu","",$forms->userdetails();,"");

the $forms->userdetails comes up on the page before the $tables->a does

any ideas or help is appreiciated