From 67861a4df8a5abdd70651d47cf265b20c41d2acc Mon Sep 17 00:00:00 2001
From: John Turner <jturner.usa@gmail.com>
Date: Wed, 26 Nov 2025 19:22:50 +0000
Subject: add SeparatedByWithOptTrailing combinator

---
 src/lib.rs | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/src/lib.rs b/src/lib.rs
index 0d5a164..220adb5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -190,6 +190,19 @@ pub trait Parser<I: Input>: Sized {
         }
     }
 
+    fn separated_by_with_opt_trailing<P>(
+        self,
+        delimiter: P,
+    ) -> impl ParserIter<I, Item = Self::Output>
+    where
+        P: Parser<I>,
+    {
+        SeparatedByWithOptTrailing {
+            parser: self,
+            delimiter,
+        }
+    }
+
     fn find(self) -> impl ParserIter<I, Item = Self::Output> {
         Find { parser: self }
     }
@@ -342,6 +355,42 @@ where
     }
 }
 
+struct SeparatedByWithOptTrailing<P1, P2> {
+    parser: P1,
+    delimiter: P2,
+}
+
+impl<I, P1, P2> ParserIter<I> for SeparatedByWithOptTrailing<P1, P2>
+where
+    I: Input,
+    P1: Parser<I>,
+    P2: Parser<I>,
+{
+    type Item = P1::Output;
+
+    fn next<OM: Mode, EM: Mode>(
+        &self,
+        it: InputIter<I>,
+        _: &mut ParserIterState,
+    ) -> Option<ParserResult<I, Self::Item, OM, EM>> {
+        if it.is_finished() {
+            None
+        } else {
+            let (rest, output) = match self.parser.run::<OM, EM>(it) {
+                Ok((rest, output)) => (rest, output),
+                Err(rest) => return Some(Err(rest)),
+            };
+
+            let rest = match self.delimiter.check(rest.clone()) {
+                Ok((rest, _)) => rest,
+                _ => rest,
+            };
+
+            Some(Ok((rest, output)))
+        }
+    }
+}
+
 struct AtLeast<P> {
     parser: P,
     count: usize,
-- 
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