samer@0: % construct - Instantiate live processing unit
samer@0: %
samer@0: % construct :: 
samer@27: %    arrow(A@typelist(N), B@typelist(M), S) ~'the arrow to instantiate',
samer@0: %    {[N]->size}                          ~'the sizes of the inputs'
samer@0: % -> unit(A,B,S)                          ~'live processing unit structure'.
samer@0: %
samer@0: % NB the type size denotes a row vector of array dimensions.
samer@0: % The type unit(A,B,S) is a structure containing
samer@0: % values and functions for running the live processing unit. Its fields
samer@0: % are as follows:
samer@0: %
samer@27: % unit(A@typelist(N),B@typelist(M),S) :== struct {
samer@0: %       starting :: () -> action ();
samer@0: %       stopping :: () -> action ();
samer@0: %       dispose  :: () -> action ();
samer@0: %       set_state :: S -> action ()
samer@0: %       get_state :: () -> S;
samer@0: %       viewables :: () -> list(samer.core.Viewable);
samer@0: %       process   :: A{:} -> B{:}
samer@0: %    }.
samer@0: 
samer@0: function u=construct(s,sizes_in)
samer@0: 	error('cannot construct system for base arrow class');
samer@0: