add include-code pandoc filter

_quarto.yml

@@ -1,6 +1,9 @@
 project:
   type: website
 
+filters:
+  - filters/include-code-files.lua
+
 website:
   title: "CEEM Gists"
   favicon: assets/ceem_logo.png

filters/include-code-files.lua

@@ -0,0 +1,62 @@
+--- include-code-files.lua – filter to include code from source files
+---
+--- Copyright: © 2020 Bruno BEAUFILS
+--- License:   MIT – see LICENSE file for details
+
+--- Dedent a line
+local function dedent (line, n)
+  return line:sub(1,n):gsub(" ","") .. line:sub(n+1)
+end
+
+--- Filter function for code blocks
+local function transclude (cb)
+  if cb.attributes.include then
+    local content = ""
+    local fh = io.open(cb.attributes.include)
+    if not fh then
+      io.stderr:write("Cannot open file " .. cb.attributes.include .. " | Skipping includes\n")
+    else
+      local number = 1
+      local start = 1
+
+      -- change hyphenated attributes to PascalCase
+      for i,pascal in pairs({"startLine", "endLine"})
+      do
+         local hyphen = pascal:gsub("%u", "-%0"):lower()
+         if cb.attributes[hyphen] then
+            cb.attributes[pascal] = cb.attributes[hyphen]
+            cb.attributes[hyphen] = nil
+         end
+      end
+
+      if cb.attributes.startLine then
+        cb.attributes.startFrom = cb.attributes.startLine
+        start = tonumber(cb.attributes.startLine)
+      end
+      for line in fh:lines ("L")
+      do
+        if cb.attributes.dedent then
+          line = dedent(line, cb.attributes.dedent)
+        end
+        if number >= start then
+          if not cb.attributes.endLine or number <= tonumber(cb.attributes.endLine) then
+            content = content .. line
+          end
+        end
+        number = number + 1
+      end 
+      fh:close()
+    end     
+    -- remove key-value pair for used keys
+    cb.attributes.include = nil
+    cb.attributes.startLine = nil
+    cb.attributes.endLine = nil
+    cb.attributes.dedent = nil
+    -- return final code block
+    return pandoc.CodeBlock(content, cb.attr)
+  end
+end
+
+return {
+  { CodeBlock = transclude }
+}