Pandoc filter in Lua to insert span into existing string

Question

I am writing a Lua filter for pandoc that adds a glossary function to HTML output of a markdown file. The goal is to add mouseover text to each occurrence of an acronym or key definition in the document.

I would like to be able to include acronyms when they occur in a list (surrounded by punctuation), but not by letters (e.g. so CO isn't highlighted in a word such as cobalt).

My MWE fails on this count because strings in the Pandoc AST include adjacent punctuation (e.g. Str "CO/DBP/SBP," or Str "CO,",Space,Str "SBP,").

-- # MWE
-- Parse glossary file (summarised here for brevity)
local glossary = {CO = "Cardiac Output", DBP = "Diastolic Blood Pressure", SBP = "Systolic Blood Pressure"}

-- Substitute glossary term for span with a mouseover link
function Str(elem)
  for key, value in next, glossary do
    if elem.text == key then
      return pandoc.Span (key, {title = value, class = "glossary"})
    end
  end
end

I have had a play with string.sub and string.find but wasn`t able to get anything workable, chiefly because I wasn't sure how to go about returning both the new Span and the Str (minus its new Span). Any help would be appreciated!

---

My test markdown contains:

# Acronyms: SBP, DBP & CO

Spaced acronyms: CO and SBP and DBP.

In a comma-separated list: CO, SBP, DBP; with backslashes; CO/DBP/SBP, and in bullet points:
  
* CO
* SBP
* DBP

Answer 1

You can just return a table with multiple elements. My idea was to look for the first separator and then replace the glossary entries with spans:

-- Parse glossary file (summarised here for brevity)
local glossary = {CO = "Cardiac Output", DBP = "Diastolic Blood Pressure", SBP = "Systolic Blood Pressure"}

local Set = function(list)
    local set = {}
    for i,v in ipairs(list) do
        set[v] = true
    end
    return set
end

local findSeparator = function(text)
    local separator = Set{",", "/", " "}
    for i = 1, #text do
        local s = string.sub(text,i,i)
        if separator[s] then
            return s
        end
    end
end

local separatedList = function(text)
    local found
    local t = {}
    local separator = findSeparator(text)
    if not separator then return end
    for abb in string.gmatch(text, "%P+") do
        if glossary[abb] then
            found = true
            t[#t+1] = pandoc.Span(abb, {title = abb, class = "glossary"})
            t[#t+1] = pandoc.Str(separator)
        end
    end
    if found then
        -- remove last separator if there are more then one elements in the list
        -- because otherwise the seperator is part of the element and needs to stay
        if #t > 2 then t[#t] = nil end
        return t
    end
end

local glossarize = {
    Str = function(el)
        if glossary[el.text] then
            return pandoc.Span(el.text, {title = glossary[el.text], class = "glossary"})
        else
            return separatedList(el.text)
        end
    end
}

function Pandoc(doc)
    local div = pandoc.Div(doc.blocks)
    local blocks = pandoc.walk_block(div, glossarize).content
    return pandoc.Pandoc(blocks, doc.meta)
end