From ba5ca7465adb2bd955bc9e64a620d175c5ef8c1f Mon Sep 17 00:00:00 2001
From: Don Yin <Don_Yin@outlook.com>
Date: Tue, 20 Oct 2026 09:56:37 +0100
Subject: [PATCH] TeX reader: accept empty delimiters in \genfrac

---
 src/Text/TeXMath/Readers/TeX.hs    | 10 +++-----
 test/reader/tex/genfrac-empty.test | 40 ++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 6 deletions(-)
 create mode 100644 test/reader/tex/genfrac-empty.test

diff --git a/src/Text/TeXMath/Readers/TeX.hs b/src/Text/TeXMath/Readers/TeX.hs
index 3a2499c9..1a24d04f 100644
--- a/src/Text/TeXMath/Readers/TeX.hs
+++ b/src/Text/TeXMath/Readers/TeX.hs
@@ -311,12 +311,10 @@ binomCmds = M.fromList
 
 genfrac :: Text -> TP Exp
 genfrac "\\genfrac" = do
-  let opener = option "" $
-                T.singleton <$> ((char '\\' >> anyChar) <|> anyChar)
-  let closer = option "" $
-                T.singleton <$> ((char '\\' >> anyChar) <|> anyChar)
-  openDelim <- braces opener <|> opener
-  closeDelim <- braces closer <|> closer
+  let delim = option "" $
+                T.singleton <$> ((char '\\' >> anyChar) <|> satisfy (/= '}'))
+  openDelim <- braces delim <|> delim
+  closeDelim <- braces delim <|> delim
   bar <- False <$ try (braces (string "0pt")) <|> True <$ texToken
   displayStyle <- True <$ try (braces (char '0')) <|> False <$ texToken
   x <- texToken
diff --git a/test/reader/tex/genfrac-empty.test b/test/reader/tex/genfrac-empty.test
new file mode 100644
index 00000000..eedca996
--- /dev/null
+++ b/test/reader/tex/genfrac-empty.test
@@ -0,0 +1,40 @@
+<<< tex
+\genfrac{}{}{0pt}{}{a}{b}
+\genfrac{}{}{1pt}{}{a}{b}
+\genfrac{}{}{1pt}{0}{a}{b}
+\genfrac{(}{}{0pt}{}{a}{b}
+\genfrac{}{)}{0pt}{}{a}{b}
+\genfrac(]{0pt}{2}{a}{b}
+
+>>> native
+[ EDelimited
+    ""
+    ""
+    [ Right (EFraction NoLineFrac (EIdentifier "a") (EIdentifier "b"))
+    ]
+, EDelimited
+    ""
+    ""
+    [ Right (EFraction NormalFrac (EIdentifier "a") (EIdentifier "b"))
+    ]
+, EDelimited
+    ""
+    ""
+    [ Right (EFraction DisplayFrac (EIdentifier "a") (EIdentifier "b"))
+    ]
+, EDelimited
+    "("
+    ""
+    [ Right (EFraction NoLineFrac (EIdentifier "a") (EIdentifier "b"))
+    ]
+, EDelimited
+    ""
+    ")"
+    [ Right (EFraction NoLineFrac (EIdentifier "a") (EIdentifier "b"))
+    ]
+, EDelimited
+    "("
+    "]"
+    [ Right (EFraction NoLineFrac (EIdentifier "a") (EIdentifier "b"))
+    ]
+]