gistfile1.rb

FIELDS_TEXT = "class A; def a; @a = @b; end; end"
FIELDS_SEXP = Ripper.sexp(FIELDS_TEXT)

[:program, [[:class, [:const_ref, [:@const, "A", [1, 6]]], nil, 
  [:bodystmt, [[:def, [:@ident, "a", [1, 13]], [:params, nil, nil, nil, nil, nil], 
  [:bodystmt, [[:assign, [:var_field, [:@ivar, "@a", [1, 16]]], 
                         [:var_ref, [:@ivar, "@b", [1, 21]]]]], nil, nil, nil]]], nil, nil, nil]]]]