add function TableEmpty()

1 files changed, 29 insertions, 1 deletions

diff --git a/_extensions/ruc-play/semantic-markdown/semantic-markdown.lua b/_extensions/ruc-play/semantic-markdown/semantic-markdown.lua
index 42101b5..59195c2 100644
--- a/_extensions/ruc-play/semantic-markdown/semantic-markdown.lua
+++ b/_extensions/ruc-play/semantic-markdown/semantic-markdown.lua
@@ -111,6 +111,16 @@
 -- @see <https://pandoc.org/lua-filters.html#common-pitfalls>
 os.setlocale 'C'
 
+-- flag running with older release of Pandoc
+--
+-- Some Pandoc features,
+-- notably pandoc.List:at() introduced wit Pandoc 3.5,
+-- are unavailable in older Pandoc releases still in widespread use
+-- due to complexities of keeping Haskell dependencies in sync.
+-- @see <https://bugs.debian.org/1098377>
+local PANDOC_IS_OLD <const> = PANDOC_VERSION[1] < 3
+ or (PANDOC_VERSION[1] == 3 and PANDOC_VERSION[2] < 5)
+
 --- pseudo-enum table to track parser enclosure state
 --- @see <https://stackoverflow.com/a/70529481/18619283>
 local Enclosure = {
@@ -161,6 +171,22 @@ local CURIE_DEFAULT <const> = ":"
 -- TODO: maybe support overriding context with a JSON-LD URI
 -- @see <https://www.w3.org/2011/rdfa-context/rdfa-1.1>
 
+--- TableEmpty - check if Pandoc List contains any elements
+---
+--- Use a workaround for Pandoc releases older than 3.5
+--- where ergonomic function pandoc.List:at() is missing.
+---
+--- @param list  Pandoc List to inspect
+--- @return      result of inspection as boolean
+local function TableEmpty(list)
+  if PANDOC_IS_OLD then
+    local list_clone = list:clone()
+    return not list_clone:remove()
+  else
+    return list:at(1) == nil
+  end
+end
+
 --- Namespaces - process RDF namespace IRI declarations
 ---
 --- Takes as input a list of Para block elements.
@@ -422,7 +448,9 @@ local function Statements (block)
         end
 
         -- qualify completed bracketed enclosure
-        elems:extend(elems_enclosed)
+        if not TableEmpty(elems_enclosed) then
+          elems:extend(elems_enclosed)
+        end
 
         elems_enclosed = pandoc.List()
         elems_unenclosed = pandoc.List()