Loading packages in custom class based on option

Question

I'd like to define a custom documentclass for assignments which can be optionally passed the minionpro argument to use the Adobe Minion Pro font; if it's not set, the Adobe Utopia font (fourier) shall be used. Now, no matter what I try, pdfLaTeX always spits out the following error:

! LaTeX Error: Missing \begin{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.8 \DeclareOption(mi
                     nionpro){

Here is the mwe.cls:

\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{mwe}[2015/12/07 mwe.cls]

\DeclareOption(minionpro){
    % Adobe Minion Pro font for the document, Euler font for math
    \RequirePackage{MinionPro}
    \RequirePackage{eulervm}
}

\DeclareOption(utopia){
    % Adobe Utopia font for the document
    \RequirePackage{fourier}
}

\ExecuteOptions{utopia}
\ProcessOptions\relax
\endinput

And here the mwe.tex

\documentclass{mwe2}
\begin{Document}
content...
\end{Document}

Alternatively, I tried using the etoolbox package to work around the package loading inside of the options, but that gave me the same error. Nevertheless, here the modified mwe.cls:

\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{mwe}[2015/12/07 mwe.cls]
\RequirePackage{etoolbox}

\providebool{minionpro}
\setbool{minionpro}{false}

\DeclareOption(minionpro){
    \setbool{minionpro}{true}
}


\ProcessOptions\relax

\ifthenelse{minionpro}{
    % Adobe Minion Pro font for the document, Euler font for math
    \RequirePackage{MinionPro}
    \RequirePackage{eulervm}
}{
    % Adobe Utopia font for the document
    \RequirePackage{fourier}
}

\endinput

Answer 1

The command \ifthenelse is in the ifthen package. If you want to check whether a boolean bool is true you can use the command \ifthenelse{\boolean{bool}}{}{}. Also I think that you have to declare the boolean values before using the \newboolean command.

Additionally as already pointed out by Nicola Talbot in the comments the \DeclareOption command needs curly brackets {} instead of ().

I think the following version of mwe.cls should work:

\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{mwe}[2015/12/07 mwe.cls]

\RequirePackage{ifthen}
\newboolean{minionpro}
\newboolean{utopia}


\DeclareOption{minionpro}{%
    % Adobe Minion Pro font for the document, Euler font for math
    \setboolean{minionpro}{true}}

\DeclareOption{utopia}{%
    % Adobe Utopia font for the document
    \setboolean{utopia}{true}}

\ExecuteOptions{utopia}
\ProcessOptions\relax

\ifthenelse{\boolean{minionpro}}{%
    \RequirePackage{MinionPro}
    \RequirePackage{eulervm}}{}
\ifthenelse{\boolean{utopia}}{%
    \RequirePackage{fourier}}{}

\endinput

EDIT: In the following an alternative version using etoolbox instead of ifthen:

\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{mwe}[2015/12/07 mwe.cls]

\RequirePackage{etoolbox}
\newbool{minionpro}
\newbool{utopia}

\DeclareOption{minionpro}{%
    % Adobe Minion Pro font for the document, Euler font for math
    \booltrue{minionpro}}

\DeclareOption{utopia}{%
    % Adobe Utopia font for the document
    \booltrue{utopia}}

\ExecuteOptions{utopia}
\ProcessOptions\relax
\ifbool{minionpro}{%
    \RequirePackage{MinionPro}
    \RequirePackage{eulervm}}{}
\ifbool{utopia}{\RequirePackage{fourier}}{}

\endinput