problem with function trees

[Dave Morse]

I'm trying to figure out the types of function arguments, but bonking.
Please help me understand what is going on here.  

  void set_nchicken( int n );

For the above function, I have a tree, t, with code FUNCTION_DECL.
TREE_VALUE (TYPE_ARG_TYPES (t)) returns a tree which should be the type of
the first argument.  TYPE_NAME of that returns null.  I was expecting a
TYPE_DECL who describes the name of the type.

Hrmph.