Returns a callback object for the transformation component.
In the uneval paper the input to the transformation component is an 8-tuple (E,V,D_G,D_L,r,p,n).
This callback allows the transformer to access most of these components:
E: This is passed directly to the transformer (see Unevalizer.uneval)
of either constants or identifiers. For example: eval("x = " + (f() + "yy")) will have the normal form "\"x = \" + TAJS_ID42"
where TAJS_ID42 is a place holder identifier representing the value of the subexpression.
V: The transformer can query information about the abstract value of the place holders using the CallBack functions.
D_G,D_L: The functions anyGlobalVariable and getNonGlobalIdentifiers allow access to this
D_M: TODO: Not implemented.
r: Direct parameter in the call to uneval() in JSGlobal and others.
p: TODO: Not implemented.
n: TODO: Not implemented.