Curved arrow from number to number in a function-table

\documentclass[a4paper]{article} % use larger type; default would be 10pt
\usepackage[margin=1in]{geometry}

\usepackage{pstricks-add,ragged2e,array}
\newcolumntype{P}[1]{>{\Centering}p{#1}}

\psset{nodesep=5pt,linearc=19pt,arrowinset=0}
\def\Line#1#2{%
  \ncbar[angle=-90,offset=1pt,arm=20pt,arrows=->]{#1}{#2}\bput*{:U}{$\cdot b$}%
  \psline[ArrowInside=->,linestyle=none]%
    (!\psGetNodeCenter{#1}#1.x #1.y 0.89 sub)(!\psGetNodeCenter{#2}#2.x #2.y 0.89 sub)}

\begin{document}

\begin{center}
\renewcommand{\arraystretch}{1.6}
\begin{tabular}{>{$}P{2cm}<{$} | *4{P{2cm}}}
x     &0  & 1& 2  &3\\\hline
f(x)  &\rnode[b]{A}{$b$}            & \rnode[b]{B}{$b \cdot a$} 
      &\rnode[b]{C}{$b \cdot a^2$}  & \rnode[b]{D}{$b\cdot a^3$}\\
      & \rule{0pt}{30pt} \Line{A}{B}\Line{B}{C}\Line{C}{D}
\end{tabular}
\end{center}

\end{document}

Luckily it is OK to nest pspictures.

\documentclass[a4paper]{article} % use larger type; default would be 10pt
\usepackage[margin=1in]{geometry}
\renewcommand{\baselinestretch}{1.6}

\usepackage{pst-node,amsmath}

\usepackage{array}
\newcolumntype{P}[1]{>{\centering\arraybackslash}p{#1}}

\psset{nodesep=7pt,linearc=19pt,linecolor=black,arrowinset=0}
\def\lbl#1{\bput*{:U}{\text{#1}}\ncput{\begin{pspicture}(-0.2,-0.1)(0.2,0.1)
\psline{->}(-0.2,0)(0.2,0)\end{pspicture}}}

\begin{document}