This is the binding function used when the formal parameter of a function is TAB. This means that we are dealing with a function of the form f(...):.... Hence, we must bind every actual parameter to a formal parameter, one by one (provided that the sizes are the same; if(siz = size(tbP),). The way the binding happens depends on the kind of formal argument. If the formal argument is just a variable, we must bind the evaluated actual argument to that formal argument. If the formal argument is an invocation, we must bind the actual argument as a function to the formal argument. Hence, the decision of what to bind depends on the tag of the formal argument. Therefore, this tag is used to select the correct 'forma-actual-binding-function' in the bind_case.