io_lib:format/2 does not return a flat string, lists:concat produces a more pretty-printable result.

src/erlydtl/erlydtl_scanner.erl

@@ -197,7 +197,7 @@ scan([H | T], Scanned, {Row, Column}, {in_code, Closer}) ->
         digit ->
             scan(T, [{number_literal, {Row, Column}, [H]} | Scanned], {Row, Column + 1}, {in_number, Closer});
         _ ->
-            {error, io_lib:format("Illegal character line ~p column ~p", [Row, Column])}
+            {error, lists:concat(["Illegal character line ", Row, " column ", Column])}
     end;
 
 scan([H | T], Scanned, {Row, Column}, {in_number, Closer}) ->
@@ -205,7 +205,7 @@ scan([H | T], Scanned, {Row, Column}, {in_number, Closer}) ->
         digit ->
             scan(T, append_char(Scanned, H), {Row, Column + 1}, {in_number, Closer});
         _ ->
-            {error, io_lib:format("Illegal character line ~p column ~p", [Row, Column])}
+            {error, lists:concat(["Illegal character line ", Row, " column ", Column])}
     end;
 
 scan([H | T], Scanned, {Row, Column}, {in_identifier, Closer}) ->
@@ -215,7 +215,7 @@ scan([H | T], Scanned, {Row, Column}, {in_identifier, Closer}) ->
         digit ->
             scan(T, append_char(Scanned, H), {Row, Column + 1}, {in_identifier, Closer});
         _ ->
-            {error, io_lib:format("Illegal character line ~p column ~p", [Row, Column])}
+            {error, lists:concat(["Illegal character line ", Row, " column ", Column])}
     end.
 
 % internal functions