[Tex/LaTex] Shortcut for arrows on curves in TikZ

Question

If I want to draw a curve with an arrow somewhere along its length (say 40% along), I can write this:

\draw [decoration={
             markings,
             mark=at position 0.4 with \arrow{>}}
       ,postaction=decorate]
       (A) to (B);

If I want to draw lots of curves with the same decoration, I can put most of this in a scope and reduce how much I have to type for each path.

However, if I want to draw lots of curves with different parameters – say, each one needs to have the arrow at a different position, and the choice of < or > could vary between curves. Then it seems I have a lot of typing to do for each curve.

What I'd like to do is define something like this:

\newcommand\arrowdata[2]{decoration={
             markings,
             mark=at position #1 with \arrow{#2}}
       ,postaction=decorate}

Then I can draw my arrows with ease:

\draw [\arrowdata{0.3}{>}] (A) to (B);
\draw [\arrowdata{0.95}{<}] (C) to (D) to (E);

and so on. But, this doesn't work, and I don't understand the error messages that result. Clearly I'm being too naive in my understanding of how macros apply in TikZ. Can someone help me out?

Answer 1

Macros in style definitions don't work if they aren't expanded beforehand. You should define your own style instead.

\tikzset{arrow data/.style 2 args={%
      decoration={%
         markings,
         mark=at position #1 with \arrow{#2}},
         postaction=decorate}
      }%
}

The use it like:

\draw [arrow data={0.3}{>}] (A) to (B);