Using trait objects seems good so far.

src/parser/nom_context.rs

@@ -3,21 +3,17 @@ use nom::error::VerboseError;
 use nom::IResult;
 
 #[derive(Clone)]
-pub struct NomContext
+pub struct NomContext {
-// where
+    pub fail_matcher: &dyn FnMut(&str) -> IResult<&str, &str, VerboseError<&str>>,
-//     F: for<'a> FnMut(&'a str) -> IResult<&'a str, &'a str, VerboseError<&'a str>>,
+    /// You can't have nested bolds or links in org-mode
-//     F: Clone,
-{
-    // pub fail_matcher: F,
-    /// You can't have nested bolds in org-mode
     pub can_match_bold: bool,
     pub can_match_link: bool,
 }
 
 impl NomContext {
-    pub fn new(fail_matcher: F) -> Self {
+    pub fn new(fail_matcher: &dyn FnMut(&str) -> IResult<&str, &str, VerboseError<&str>>) -> Self {
         NomContext {
-            // fail_matcher,
+            fail_matcher,
             can_match_bold: true,
             can_match_link: true,
         }