Lua code for association lists on the command line (for use with fish)

assoc.lua

#!/usr/bin/env lua5.1

-- assocation list on the command line
--
-- rep is: key1 val1 key2 val2 ...
--

local function succeed(s)
  if s ~= true then
    io.stdout:write(s, '\n')
  end
  os.exit(0)
end

local function fail()
  os.exit(1)
end

local function finish(answer)
  if answer then
    io.stdout:write(answer, '\n')
    os.exit(0)
  else
    os.exit(1)
  end
end


local funs = { }

function funs.index(key, ...)
  local args = { ... }
  for i = 1, #args, 2 do
    if args[i] == key then
      return i
    end
  end
end

function funs.get(key, ...)
  local i = funs.index(key, ...)
  if i then
    return select(i+1, ...)
  end
end

function funs.has(key, ...)
  return funs.index(key, ...) and true or false
end

function funs.keys(...)
  local args = { ... }
  for i = 1, #args, 2 do
    io.stdout:write(args[i], '\n')
  end
  os.exit(0)
end

function funs.set(key, value, ...)
  local args = { ... }
  local i = funs.index(key, ...)
  if not i then
    i = #args + 1
    args[i] = key
  end
  args[i+1] = value
  for _, s in ipairs(args) do
    io.stdout:write(s, '\n')
  end
  os.exit(0)
end
    

local operation = assert(table.remove(arg, 1))
finish(assert(funs[operation])(unpack(arg)))