Is there an \iftex4ht command, and if not, how should it be defined?

Question

Background: I'm using TikZ to generate a load of pictures that I want to put on the web as SVGs. So I'm using the pgfsys-tex4ht.def driver and it's working very well. My gut feeling is that the SVG output from TikZ/pgf is "experimental" so while designing the pictures, I'm not using a special driver but just generating the PDFs via pdflatex. Also, I want PDFs as well as SVGs at the end.

So rather than having to comment out the line

\def\pgfsysdriver{pgfsys-tex4ht.def}

each time, I'd rather have a switch that loaded it if tex4ht was loaded; that is, I already specify the output when I decide whether to run pdflatex or htlatex - I don't want to have to specify it twice. So, my question:

Is there an \iftex4ht somewhat akin to the \ifpdf provided by ifpdf.sty?
If not, what would be the "right" way to test for the presence of tex4ht?

Answer 1

There is always this:

\@ifpackageloaded{tex4ht}{LOADED}{NOT LOADED}

Suitable for other packages of interest as well, of course. (Usual caveats about @ character apply.)

Answer 2

Based on Harald's answer you can define your \iftex4ht as follows.

\documentclass{article}
%\usepackage{tex4ht}
\makeatletter
\@ifpackageloaded{tex4ht}{\def\iftex4ht{\iftrue}}
                         {\def\iftex4ht{\iffalse}}
\makeatother

\begin{document}
\iftex4ht TeX4ht\else no!\fi
\end{document}

OK, this answer is kind of a joke, but I wanted to point out that you can't use \newif\iftex4ht or \newcommand\iftex4ht since 4 is not letter. With \def it works (delimited macro with no arguments), but you can't nest it in other \ifs since TeX doesn't see that it's an \if.

Answer 3

A conditional named \iftex4ht is impossible to define without side effects. However using directly \@ifpackageloaded{tex4ht} has a big limitation, because it's allowed only in the preamble.

There are a few strategies to circumvent the problem: all use \@ifpackageloaded in the preamble to define something that one will be able to use also in the body of the document.

1. Primitive conditional syntax

   \makeatletter
   \@ifpackageloaded{tex4ht}
     {\let\iftexforht\iftrue}
     {\let\iftexforht\iffalse}
   \makeatother
   

   and use \iftexforht just like any of the primitive conditionals.

2. LaTeX pseudoconditional

   \makeatletter
   \@ifpackageloaded{tex4ht}
     {\let\iftexforht\@firstoftwo}
     {\let\iftexforht\@secondoftwo}
   \makeatother
   

   to be used like

   \iftexforht{<code for TeX4ht>}{<code when TeX4ht isn't used>}
   

3. Almost like a primitive conditional

   \makeatletter
   \edef\texforht{TT\noexpand\fi
     \@ifpackageloaded{tex4ht}
       {\noexpand\iftrue}
       {\noexpand\iffalse}}
   \makeatother
   

   to be used as

   \if\texforht
     <code for TeX4ht>
   \else
     <code when TeX4ht isn't used>
   \fi
   

Which one to prefer is a matter of taste. Both the first and third methods allow conditional nesting.