samer@0: % afield - arrow to extract named field from structure
samer@0: %
samer@0: % afield :: N:string ~'field name' -> arrow({struct{N::T;}, {T}, empty).
samer@0: %
samer@0: % If input is structure with a field named N of type T,
samer@0: % the single output is of type T.
samer@0: function o=afield(nm,sz)
samer@0: 	o=arr(@(x)getfield(x,nm),'sizefn',@(s){sz});
samer@0: end