LaTeX reader: improve handling of plain TeX macro primitives.

- Fixed semantics for `\let`.
- Implement `\edef`, `\gdef`, and `\xdef`.
- Add comment noting that currently `\def` and `\edef` set global
  macros (so are equivalent to `\gdef` and `\xdef`).  This should be
  fixed by scoping macro definitions to groups, in a future commit.

Closes #7474.

1 files changed, 37 insertions, 1 deletions

diff --git a/test/command/macros.md b/test/command/macros.md
index e3c07e661..9f7a0f9d3 100644
--- a/test/command/macros.md
+++ b/test/command/macros.md
@@ -25,7 +25,7 @@ expanded at point of use:
 ```
 % pandoc -f latex -t latex
 \let\a\b
-\newcommand{\b}{\emph{ouk}}
+\def\b{\emph{ouk}}
 \a a
 ^D
 a̱
@@ -123,3 +123,39 @@ hello+hello
 hello+goodbye
 ```
 
+```
+% pandoc -f latex -t plain
+\def\txt{a}
+\def\foo{\txt}
+\let\bar\foo
+\bar % -> a
+\def\txt{b}
+\bar % -> b
+\def\foo{OH}
+\bar % -> b
+^D
+a b b
+```
+
+```
+% pandoc -f latex -t plain
+\def\aaa{aaa}
+\def\bbb{x\aaa}
+\edef\ccc{y\aaa}
+\def\aaa{AAA}
+\bbb \ccc
+^D
+xAAAyaaa
+```
+
+```
+% pandoc -f latex -t plain
+\gdef\aaa{aaa}
+\gdef\bbb{x\aaa}
+\xdef\ccc{y\aaa}
+\gdef\aaa{AAA}
+\bbb \ccc
+^D
+xAAAyaaa
+```
+