How to set horizontal alignment inside a custom environment, based on one of the parameters

Question

So with this code using xparse :

\NewDocumentEnvironment{figwcommentary}{O{0.45} m m}
{ \adjustbox{valign=t} {\begin{minipage}{#1\textwidth} #2 \end{minipage} } }
{ \adjustbox{valign=t,right=0.5\textwidth}{ #3 } \bigskip}

That right=0.5\textwidth} should be right=(1-#1-.05)*\textwidth} which of course isn't valid code.

It looks like calc or fp can be used for this, but I can't figure out how to reference the passed parameter.

Answer 1

Not as hard as I thought :

\NewDocumentEnvironment{figwcommentary}{O{0.45} m m}
{ 
\FPeval\adjustedlen{1-#1-0.05}
\adjustbox{valign=t} {\begin{minipage}{#1\textwidth} #2 \end{minipage} } }
{ \adjustbox{valign=t,right=\adjustedlen\textwidth}{ #3 } \bigskip}