Make LaTeX colons have the spacing of \colon, e.g. for typing judgements.tex

Make LaTeX colons have the spacing of \colon, e.g. for typing judgements.tex

\documentclass[]{article}

% Make `:` behave as if you typed `\colon`.
% In particular, this allows you to concisely write `t: A` for a typing assertion while still
% getting the correct spacing of `\colon`.
%
% source: <https://chat.stackexchange.com/transcript/message/56900862#56900862>
% author: Skillmon <https://tex.stackexchange.com/users/117050/skillmon>
\begingroup
\lccode`\~=`\:
\lowercase{\endgroup\def~}{\colon}
\AtBeginDocument{\mathcode`\:="8000 }

\begin{document}
  % Both lines have the same spacing
  $a\colon b$\par
  $a: b$\par
\end{document}