Small letters as input but capital letters as output

Question

Is it possible to define (or is there already) a macro which takes small letters as input but gives the same letters in capital as output?

Example:

\CapLet{horse} and \CapLet{fish}

wiht the output

HORSE and FISH

Answer 1

\MakeUppercase converts the case of its argument to UPPER CASE.

\documentclass{article}
\let\CapLet\MakeUppercase
\let\LowLet\MakeLowercase
\begin{document}
\CapLet{horse} and \CapLet{fish} \par
\LowLet{HORSE} AND \LowLet{FISH}
\end{document}

It uses the TeX primitive \uppercase internally. A comparable \MakeLowercase exists.