key-value dictionary
petr olsak provides this example in tex in a nutshell:
\def\keyval #1 #2 {\expandafter\def\csname dict:#1\endcsname{#2}}
\def\value #1 {\csname dict:#1\endcsname}
\keyval Peter 21 % key=Peter, value=21, saved to the dictionary
% it does \def\dict:Peter{21}
\value Peter % expands to \dict:Peter which expands to 21.this is basically defining macros with real funky names you couldn't accidentally type