Package with environment that changes according to option

Question

I've been trying to write a small package so I can show/hide solutions in some of my notes, so far I have the following non working example which I hacked by looking at some other answers and the latex wiki book https://en.wikibooks.org/wiki/LaTeX/Plain_TeX#Self_defined_conditionals

\ProvidesPackage{solutions}

\newif\ifsolutions
\solutionsfalse
\DeclareOption{solutions}{\solutionstrue}
\DeclareOption{nosolutions}{\solutionsfalse}

\newenvironment{solution}[1]{
    \ifsolutions
       #1 $\delta$ % I'd ideally want to write the solution in a gray box
    \else 
       #1 $\bullet$ % I'd like to ignore all the input when solutions is false, but putting a circle will do for now.
    \fi
}

and my .tex

\documentclass[reqno, 12pt, twoside, letterpaper]{memoir}
\usepackage[nosolutions]{packages/solutions}
\begin{document}
  \begin{solution}
    Test
  \end{solution}
\end{document}

But this doesn't work at all, if I define solutions it doesn't work and if I define nosolutions it will fail to compile. I've been searching for a way to use an if inside the new environment with nothing that looks even remotely promising.

Any ideas on where I should look for this?

Answer 1

You need \ProcessOptions\relax to handle package options.

\ProvidesPackage{solutions}

\newif\ifsolutions
\solutionsfalse
\DeclareOption{solutions}{\solutionstrue}
\DeclareOption{nosolutions}{\solutionsfalse}
\ProcessOptions\relax
\newenvironment{solution}[1]{
    \ifsolutions
       #1 $\delta$ % I'd ideally want to write the solution in a gray box
    \else 
       #1 $\bullet$ % I'd like to ignore all the input when solutions is false, but putting a circle will do for now.
    \fi
}{}