Drawing a half arrow with tikz

Question

Is there a command to draw upper half of an arrow in tikz? Something similar to:

Answer 1

This can be easily obtained via arrows.meta library in PGF 3.0. The shape you requested belong to the Staight Barb family (See PGF 3.0 documentation page 206). As a MWE, see this simple code and the output below it:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\begin{document}

\begin{tikzpicture}
\draw [-{Straight Barb[left]}] (0,0)--(0.5,0);
\end{tikzpicture}

\end{document}

The output here is:

Answer 2

You can also use a symbol from latexsym package.

\documentclass{article}
\usepackage{latexsym}

\begin{document}

$\rightharpoonup$

$\rightharpoondown$

\end{document}