2 1 : , : , { } parallel :wait => do 1 end loop pre_test{ } post_test{ } do 1 end choose do 1 end critical : do 1 end 1 alternative do 1 end 1 otherwise do 1 end 1 parallel_branch do | | 1 end : , : => { } nil " " : => , do | | , <<-end 1 end