From 57058764776fa3d9aa0d75bbe6875fd1414c0d48 Mon Sep 17 00:00:00 2001
From: Greg Shuflin <greg.shuflin@protonmail.com>
Date: Thu, 20 Oct 2022 23:29:06 -0700
Subject: [PATCH] Separated by

---
 src/combinators.rs | 72 +++++++++++++++++++++++++++++++++++++---------
 1 file changed, 59 insertions(+), 13 deletions(-)

diff --git a/src/combinators.rs b/src/combinators.rs
index b7302d0..5f2fe80 100644
--- a/src/combinators.rs
+++ b/src/combinators.rs
@@ -49,15 +49,16 @@ where
         }
     }
 
-    pub fn delimited_by<D, O2>(self, delimiter: D) -> DelimitedBy<'a, I, O>
+    pub fn separated_by<D, O2>(self, delimiter: D, allow_trailing: bool) -> SeparatedBy<'a, I, O>
     where
         D: Parser<I, O2, I> + 'a,
         O2: 'a,
         I: 'a,
     {
-        DelimitedBy {
+        SeparatedBy {
             inner_repeated: self,
             delimiter: BoxedParser::new(delimiter.to(())),
+            allow_trailing,
         }
     }
 }
@@ -94,21 +95,24 @@ where
     }
 }
 
-pub struct DelimitedBy<'a, I, O>
+pub struct SeparatedBy<'a, I, O>
 where
     I: Clone,
 {
     inner_repeated: Repeated<'a, I, O>,
     delimiter: BoxedParser<'a, I, (), I>,
+    allow_trailing: bool,
 }
 
-impl<'a, I, O> Parser<I, Vec<O>, I> for DelimitedBy<'a, I, O>
+impl<'a, I, O> Parser<I, Vec<O>, I> for SeparatedBy<'a, I, O>
 where
     I: Clone + 'a,
 {
     fn parse(&self, input: I) -> ParseResult<I, Vec<O>, I> {
         let at_least = self.inner_repeated.at_least.unwrap_or(0);
         let at_most = self.inner_repeated.at_most.unwrap_or(u16::MAX);
+        let parser = &self.inner_repeated.inner_parser;
+        let delimiter = &self.delimiter;
 
         if at_most == 0 {
             return Ok((vec![], input));
@@ -116,20 +120,51 @@ where
 
         let mut results = Vec::new();
         let mut count: u16 = 0;
-        let mut further_input = input.clone();
+        let mut further_input;
+
+        match parser.parse(input.clone()) {
+            Ok((item, rest)) => {
+                results.push(item);
+                further_input = rest;
+            }
+            Err(_e) => {
+                if at_least > 0 {
+                    return Err(input);
+                } else {
+                    return Ok((vec![], input));
+                }
+            }
+        }
+
+        loop {
+            match delimiter.parse(further_input.clone()) {
+                Ok(((), rest)) => {
+                    further_input = rest;
+                }
+                Err(_e) => {
+                    break;
+                }
+            }
+
+            match parser.parse(further_input.clone()) {
+                Ok((item, rest)) => {
+                    results.push(item);
+                    further_input = rest;
+                    count += 1;
+                }
+                Err(_e) if self.allow_trailing => {
+                    break;
+                }
+                Err(e) => {
+                    return Err(e);
+                }
+            }
 
-        while let Ok((item, rest)) = self
-            .inner_repeated
-            .inner_parser
-            .parse(further_input.clone())
-        {
-            results.push(item);
-            further_input = rest;
-            count += 1;
             if count >= at_most {
                 break;
             }
         }
+
         if count < at_least {
             return Err(input);
         }
@@ -175,4 +210,15 @@ mod tests {
         assert_eq!(output.len(), 1);
         assert_eq!(rest, "ecks");
     }
+
+    #[test]
+    fn test_separated_by() {
+        let p = repeated(literal("garb").to(20))
+            .separated_by(repeated(literal(" ")).at_least(1), false);
+
+        assert_eq!(
+            p.parse("garb garb      garb     garb").unwrap(),
+            (vec![20, 20, 20, 20], "")
+        );
+    }
 }