* lisplib.c (struct_set_entries): Trigger autoload on new symbols define-struct-clause and *struct-clause-expander*. * stdlib/struct.tl (*struct-clause-expander*): New variable. (defstruct): expand-slot local function now returns list of expanded slots, not a single slot; every case in the tree-case is converted to return a list. The syntax of a slot clause is first expanded through *struct-clause-expander hash; if that works then the resulting list is further scanned for expansions. (define-struct-clause): New macro. (:delegate): New struct clause defined with define-struct-clause. Provides single-slot delegation. * tests/012/oop.tl: Tests for :delegate. * txr.1: Documented define-struct-clause and :delegate. * stdlib/doc-syms.tl: Updated.