use Result type instead of raising exception

lib/frontmatter.ml

@@ -1,8 +1,6 @@
 module Y = Hl_yaml.Unix
 module StringMap = Map.Make (String)
 
-exception Frontmatter_parse_error of string
-
 (* Type for frontmatter data *)
 type t = Yojson.Safe.t StringMap.t
 
@@ -56,15 +54,10 @@ let yojson_to_string_map = function
            StringMap.empty assoc)
   | _ -> Error "Frontmatter must be a YAML object/map"
 
-let parse_frontmatter (yaml_content : string) : t =
-  if String.trim yaml_content = "" then StringMap.empty
-  else
-    try
-      let options = Y.make_options ~enable_imports:false () in
-      let result =
-        Y.parse ~options ~of_yojson:yojson_to_string_map yaml_content
-      in
-      Y.ok_or_raise result
-    with exn ->
-      raise
-        (Frontmatter_parse_error ("Parsing failed: " ^ Printexc.to_string exn))
+let parse_frontmatter (yaml_content : string) : (t, string) Result.t =
+  let options = Y.make_options ~enable_imports:false () in
+  match Y.parse ~options ~of_yojson:yojson_to_string_map yaml_content with
+  | Ok fm -> Ok fm
+  | Error error_list ->
+      Error
+        (List.map Hl_yaml.Spec.error_to_string error_list |> String.concat "\n")

lib/frontmatter.mli

@@ -25,9 +25,6 @@ module StringMap : Map.S with type key = string
 type t = Yojson.Safe.t StringMap.t
 (** Type representing the frontmatter as a map of string keys to JSON values. *)
 
-exception Frontmatter_parse_error of string
-(** Exception raised when frontmatter parsing fails. *)
-
 val extract_frontmatter : string -> string * string
 (** [extract_frontmatter content] extracts the YAML frontmatter from the
     beginning of the markdown content. It returns the YAML part and the rest of
@@ -45,22 +42,17 @@ val extract_frontmatter : string -> string * string
     markdown file, it must not be silently parsed as content. A YAML parsing
     error whenever the parsing happens is desired instead. *)
 
-val parse_frontmatter : string -> t
+val parse_frontmatter : string -> (t, string) Result.t
 (** [parse_frontmatter content] parses YAML frontmatter from a string.
 
     @param content The frontmatter part of the markdown content
     @return
-      A map where keys are frontmatter field names and values are the
-      corresponding JSON values preserving their original types
-
-    @raise Frontmatter_parse_error
-      if the YAML parsing fails or if the frontmatter is not a valid YAML
-      object/map
+      A result object which when Ok, contains a map where keys are frontmatter
+      field names and values are the corresponding JSON values preserving their
+      original types. When error, contains an error message indicating the
+      parsing failure(s).
 
     Returns an empty map if:
     - The frontmatter section is empty
 
-    The function expects frontmatter to be:
-    - Valid YAML that parses to an object/map structure
-
     Security note: File imports are disabled during parsing for security. *)

lib/page.ml

@@ -1,7 +1,3 @@
 module UserPage = struct
   type t = { frontmatter : Frontmatter.t; content : string }
-
-  (* let of_string (content : string) : t =
-    match Frontmatter.extract_frontmatter content with
-    | (yaml_content, remaining_content) -> *)
 end

test/test_frontmatter.ml

@@ -75,19 +75,20 @@ let%test "extract content from md with invalid frontmatter" =
   String.trim content = {|" # bad yaml|}
 
 let%test "parse valid yaml" =
-  let fm = parse_frontmatter simple_markdown_yaml_section in
-  let expected =
-    StringMap.of_list
-      [
-        ("Title", `String "Test Document");
-        ("Draft", `Bool true);
-        ("Date", `String "2023-10-01");
-      ]
-  in
-  StringMap.equal Yojson.Safe.equal fm expected
+  match parse_frontmatter simple_markdown_yaml_section with
+  | Error _ -> false
+  | Ok fm ->
+      let expected =
+        StringMap.of_list
+          [
+            ("Title", `String "Test Document");
+            ("Draft", `Bool true);
+            ("Date", `String "2023-10-01");
+          ]
+      in
+      StringMap.equal Yojson.Safe.equal fm expected
 
-let%test "parse invalid yaml raises Frontmatter_parse_error" =
-  try
-    ignore (parse_frontmatter invalid_yaml_frontmatter);
-    false
-  with Frontmatter_parse_error _ -> true
+let%test "parse invalid yaml should error" =
+  match parse_frontmatter invalid_yaml_frontmatter with
+  | Error _ -> true
+  | Ok _ -> false