Harpoons in TikZ

Question

Can I have any harpoons in TikZ?

I refer to my previous question on harpoons: "How to draw protocol interaction" using amsmath.
The closest thing I have found is this code:

\begin{tikzpicture}[decoration={bent,aspect=.3}]  
    \node[circle,draw] (A) at (.5,.5) {A};   
    \node[circle,draw] (B) at (3,1.5) {B};   
    \draw[->,decorate] (A) -- (B);   
    \draw[->,decorate] (B) -- (A);  
\end{tikzpicture}  

Answer 1

There are so called partial arrow tips in TikZ. Use for instance left to, right to, left hook or right hook. They are desribed in section 23.7 of the pfg 2.10 manual (22.6 in the pgf 2.0 manual).

Inserting this into your example:

\documentclass{article} 
\usepackage{tikz}
\usetikzlibrary{arrows}
\begin{document}
\begin{tikzpicture}
    \node[circle,draw] (A) at (.5,.5) {A};   
    \node[circle,draw] (B) at (3,1.5) {B};   
    \draw[-left to] (A.north east) -- (B.west);   
    \draw[-left to] (B) -- (A);  
\end{tikzpicture}  
\end{document}