How to write a xymatrix-like LaTeX environment?

Question

I like to draw commutative diagrams using the xymatrix command. What I do not like is the fact that xymatrix is a command and not an environment. The structure of the xymatrix minilanguage is similar to some LaTeX environments that provide alignment of math formulas (array,align etc.), and it feels just weird to use a command in the xymatrix case.

I would like to define an environment that behaves exactly like the xymatrix command, but I do not know enough TeX to do that, so my naive attempts fail.

Could you write such an environment, or point me towards solution of my problem?

Answer 1

You could use the b argument type in \NewDocumentEnviornment to grab all of the content then pass to \xymatrix. For example

\documentclass{article}
\usepackage[all,cmtip]{xy}
\NewDocumentEnvironment{xyenv}{ob}{
  \IfNoValueTF{#1}{\xymatrix{#2}}{\xymatrix@#1{#2}}%
}{}
\begin{document}
\xymatrix{
U \ar@/_/[ddr]_y \ar@/^/[drr]^x
\ar@{.>}[dr]|-{(x,y)} \
& X \times_Z Y \ar[d]^q \ar[r]_p
& X \ar[d]_f \
& Y \ar[r]^g & Z }
\begin{xyenv}
  U \ar@/_/[ddr]_y \ar@/^/[drr]^x
  \ar@{.>}[dr]|-{(x,y)} \
  & X \times_Z Y \ar[d]^q \ar[r]_p
  & X \ar[d]_f \
  & Y \ar[r]^g & Z
\end{xyenv}
\xymatrix@C+1em{
U \ar@/_/[ddr]_y \ar@/^/[drr]^x
\ar@{.>}[dr]|-{(x,y)} \
& X \times_Z Y \ar[d]^q \ar[r]_p
& X \ar[d]_f \
& Y \ar[r]^g & Z }
\begin{xyenv}[C+1em]
  U \ar@/_/[ddr]_y \ar@/^/[drr]^x
  \ar@{.>}[dr]|-{(x,y)} \
  & X \times_Z Y \ar[d]^q \ar[r]_p
  & X \ar[d]_f \
  & Y \ar[r]^g & Z
\end{xyenv}
\end{document}

(In a real use, I might be minded to save \xymatrix with some internal name then create an environment called xymatrix here: for a demo, that looked a bit more risky.)