Square edges in forest package

Question

I can easily do trees with horizontal (square) edges in tikz-qtree (see MWE). The forest package is however a far superior alternative for my purposes. However, every attempt to do either horizontal or vertical trees with square edges in forest is either ignored, or leads to compilation failure (for example inserting the \tikzset line into the forest tree). Is this possible?

A helping hand would be very much appreciated here.

 \documentclass[10pt,twoside,a4paper]{memoir}
 \usepackage{graphicx}
 \usepackage{forest}
 \usepackage{tikz-qtree}

 \begin{document}

 \begin{tikzpicture}
 \tikzset{edge from parent/.style={draw,edge from parent path={(\tikzparentnode.south)-- +(0,-8pt)-| (\tikzchildnode)}}}
 \Tree [.ZZ
 [.Bax
 [.X
 [.Y [.A ] [.B ] ]
 [.Z [.C ] [.D ] ] ]
 [.F
 [.M [.E ] [.F ] ]
 [.G [.G ] [.H ] ] ] ]
 [.A
 [.B
 [.S  [.I P R T V U ] [.J ] ]
 [.I  [.K ] [.L ] ] ]
 [.M
 [.L  [.M ] [.N ] ]
 [.A  [.O ] [.P ] ] ] ] ] ]
 \end{tikzpicture}


 \begin{forest}
 [ZZ
 [Bax
 [X
 [Y [A ] [B ] ]
 [Z [C ] [D ] ] ]
 [F
 [M [E ] [F ] ]
 [G [G ] [H ] ] ] ]
 [A
 [B
 [S  [I [P][R][T][V][U]] [J ] ]
 [I  [K ] [L ] ] ]
 [M
 [L  [M ] [.N ] ]
 [A  [O ] [P ] ] ] ] ] ]
 \end{forest}

 \end{document}

Answer 1

You need to do \begin{forest} for tree={edge path=<your path>}} (without []!).

I adjusted the distance a little bit, better would be to use for example half the level distance and not a fixed distance.

One can also use my paths.ortho library (needs both tikzlibarypaths.ortho.code.tex and tikzlibarypaths.ortho.tex) and be available to use |-| instead of --.

Code

\documentclass[10pt,twoside,a4paper]{memoir}
\usepackage{graphicx}
\usepackage{forest}
\usepackage{tikz-qtree}
\begin{document}

\begin{tikzpicture}
\tikzset{edge from parent/.style={draw,edge from parent path={(\tikzparentnode.south)-- +(0,-8pt)-| (\tikzchildnode)}}}
\Tree [.ZZ
[.Bax
[.X
[.Y [.A ] [.B ] ]
[.Z [.C ] [.D ] ] ]
[.F
[.M [.E ] [.F ] ]
[.G [.G ] [.H ] ] ] ]
[.A
[.B
[.S  [.I P R T V U ] [.J ] ]
[.I  [.K ] [.L ] ] ]
[.M
[.L  [.M ] [.N ] ]
[.A  [.O ] [.P ] ] ] ] ] ]
\end{tikzpicture}


\begin{forest} for tree={
    edge path={\noexpand\path[\forestoption{edge}] (\forestOve{\forestove{@parent}}{name}.parent anchor) -- +(0,-12pt)-| (\forestove{name}.child anchor)\forestoption{edge label};}
}
[ZZ
[Bax
[X
[Y [A ] [B ] ]
[Z [C ] [D ] ] ]
[F
[M [E ] [F ] ]
[G [G ] [H ] ] ] ]
[A
[B
[S  [I [P][R][T][V][U]] [J ] ]
[I  [K ] [L ] ] ]
[M
[L  [M ] [.N ] ]
[A  [O ] [P ] ] ] ] ] ]
\end{forest}

\end{document}

Output

Answer 2

With current Forest, it is a simple question of loading the edges library and adding forked edges to the tree's preamble.

\documentclass[border=10pt]{standalone}
\usepackage[edges]{forest}
\begin{document}
\begin{forest}
  forked edges,
 [ZZ
 [Bax
 [X
 [Y [A ] [B ] ]
 [Z [C ] [D ] ] ]
 [F
 [M [E ] [F ] ]
 [G [G ] [H ] ] ] ]
 [A
 [B
 [S  [I [P][R][T][V][U]] [J ] ]
 [I  [K ] [L ] ] ]
 [M
 [L  [M ] [.N ] ]
 [A  [O ] [P ] ] ] ] ] ]
\end{forest}
\end{document}

If you have only version 1 of Forest, this won't work. In that case, you should update. If that's not possible, note that macros such as \forestove are intended as part of the internal implementation and should be avoided in end-user code as they are liable to break on update. Instead, use the wrappers which Forest provides for this purpose, which are much more likely to survive any changes to Forest's innards.

\documentclass[border=10pt]{standalone}
\usepackage{forest}% version 1
\begin{document}
\begin{forest}
  for tree={
    parent anchor=south,
    edge path={
      \noexpand\path [\forestoption{edge}] (!u.parent anchor) -- ++(0,-5pt) -| (.child anchor)\forestoption{edge label};
    }
  }
 [ZZ
 [Bax
 [X
 [Y [A ] [B ] ]
 [Z [C ] [D ] ] ]
 [F
 [M [E ] [F ] ]
 [G [G ] [H ] ] ] ]
 [A
 [B
 [S  [I [P][R][T][V][U]] [J ] ]
 [I  [K ] [L ] ] ]
 [M
 [L  [M ] [N ] ]
 [A  [O ] [P ] ] ] ] ] ]
\end{forest}
\end{document}