Create a start_of_line parser.

src/parser/document.rs

@@ -99,6 +99,29 @@ fn headline<'r, 's>(
     context: Context<'r, 's>,
     input: &'s str,
 ) -> Res<&'s str, (usize, &'s str, Vec<Object<'s>>, &'s str)> {
+    let parser_context =
+        context.with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
+            exit_matcher: ChainBehavior::AndParent(Some(&headline_end)),
+        }));
+    let standard_set_object_matcher = parser_with_context!(standard_set_object)(&parser_context);
+    let start_of_line_matcher = parser_with_context!(start_of_line)(&parser_context);
+
+    let (remaining, (_sol, star_count, ws, title, ws2)) = tuple((
+        start_of_line_matcher,
+        many1_count(tag("*")),
+        space1,
+        many1(standard_set_object_matcher),
+        alt((line_ending, eof)),
+    ))(input)?;
+    Ok((remaining, (star_count, ws, title, ws2)))
+}
+
+fn headline_end<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, &'s str> {
+    line_ending(input)
+}
+
+/// Check that we are at the start of a line
+fn start_of_line<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, ()> {
     let document_root = context.get_document_root().unwrap();
     let preceding_character = get_one_before(document_root, input)
         .map(|slice| slice.chars().next())
@@ -108,32 +131,16 @@ fn headline<'r, 's>(
         Some(_) => {
             // Not at start of line, cannot be a heading
             return Err(nom::Err::Error(CustomError::MyError(MyError(
-                "Heading not at start of line",
+                "Not at start of line",
             ))));
         }
         // If None, we are at the start of the file which allows for headings
         None => {}
     };
-
-    let parser_context =
-        context.with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
-            exit_matcher: ChainBehavior::AndParent(Some(&headline_end)),
-        }));
-    let standard_set_object_matcher = parser_with_context!(standard_set_object)(&parser_context);
-
-    let ret = tuple((
-        many1_count(tag("*")),
-        space1,
-        many1(standard_set_object_matcher),
-        alt((line_ending, eof)),
-    ))(input);
-    ret
-}
-
-fn headline_end<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, &'s str> {
-    line_ending(input)
+    Ok((input, ()))
 }
 
+/// Get one character from before the current position.
 fn get_one_before<'s>(document: &'s str, current_position: &'s str) -> Option<&'s str> {
     assert!(is_slice_of(document, current_position));
     if document.as_ptr() as usize == current_position.as_ptr() as usize {
@@ -144,6 +151,7 @@ fn get_one_before<'s>(document: &'s str, current_position: &'s str) -> Option<&'
     Some(&document[previous_character_offset..offset])
 }
 
+/// Check if the child string slice is a slice of the parent string slice.
 fn is_slice_of(parent: &str, child: &str) -> bool {
     let parent_start = parent.as_ptr() as usize;
     let parent_end = parent_start + parent.len();