I think there is an error in this file:
some o_types are declared erroneously as tap_types
here is the output of the diff between new and old:
Achilleas
diff gr_single_pole_iir.h gr_single_pole_iir_old.h
74c74
< o_type prev_output () { return d_prev_output; }
tap_type prev_output () { return d_prev_output; }
79c79
< o_type d_prev_output;
tap_type d_prev_output;
90c90
< o_type output;