How to pass PostScript expression to nodesep and offset when using ([…]node) syntax?

Question

How to pass PostScript expression to nodesep and offset when using ([...]node) syntax?

Edit: I just known that for angle, we can use PS expression such as angle={!30 60 add}.

\documentclass[pstricks,border=12pt]{standalone}
\usepackage{pstricks-add}

\begin{document}
    \begin{pspicture}[showgrid](3,3)
        \pnode{A}
        \pnode
        [!
            60 cos 3 mul
            60 sin 3 mul
        ](A){B}
        \psline{->}(A)(B)
    \end{pspicture}

%   \begin{pspicture}[showgrid](3,3)
%       \pnode{A}
%       \psline(A){->}([nodesep=,offset=]A)
%   \end{pspicture}
\end{document}

Answer 1

nodesep and offset are a length and must have a unit, at least the current one.

\documentclass{article}
\usepackage{pst-node}

\begin{document}
    \begin{pspicture}[showgrid](3,3)
        \pnode{A}
        \pnode
        [!
            60 cos 3 mul
            60 sin 3 mul
        ](A){B}
        \psline{->}(A)(B)
    \end{pspicture}

\bigskip
   \begin{pspicture}[showgrid](3,3)
       \pnode{A}
       \psline{->}(A)(!\psGetNodeCenter{A} 
         A.x 60 cos 3 mul add 
         A.y 60 sin 3 mul add)
   \end{pspicture}

\end{document}