IO category transformers

[fogfish]

%% we have a function that returns io monad
io() ->
   [m_io ||
      ...
   ].

%% we need to compose this function with other category (e.g. reader)
dot() ->
  [reader ||
     Result =< io()
     ...
  ].

The Result is IO function. We need to design a transformer to evaluate this function to actual IO result or fail.