A Lua REPL implemented in Lua

repl.lua

do
  local buffer = ''

  local function gather_results(success, ...)
    local n = select('#', ...)
    return success, { n = n, ... }
  end 

  local function print_results(results)
    local parts = {}

    for i = 1, results.n do
      parts[#parts + 1] = tostring(results[i])
    end 

    print(table.concat(parts, '  '))
  end 

  function evaluate_line(line)
    local chunk  = buffer .. line
    local f, err = loadstring('return ' .. chunk, 'REPL') -- first we prefix return

    if not f then
      f, err = loadstring(chunk, 'REPL') -- try again without return
    end 

    if f then
      buffer = ''
      local success, results = gather_results(xpcall(f, debug.traceback))

      if success then
        -- successful call
        if #results > 0 then
          print_results(results)
        end 
      else
        -- error
        print(results[1])
      end 
    else
      if err:match "'<eof>'$" then
        -- Lua expects some more input; stow it away for next time
        buffer = chunk .. '\n'
        return '>>'
      else
        print(err)
      end 
    end 

    return '>' 
  end 
end

function display_prompt(prompt)
  io.stdout:write(prompt .. ' ')
end

display_prompt '>' 
for line in io.stdin:lines() do
  local prompt = evaluate_line(line)
  display_prompt(prompt)
end

I think this piece is wrong.

    local f, err = loadstring('return ' .. chunk, 'REPL') -- first we prefix return

    if not f then
      f, err = loadstring(chunk, 'REPL') -- try again without return
    end 

For example, I have some codes "f()" to evaluate, where f will through error, no matter what happens. it also change the internal state of lua. The above scripts will cause the internal state to change twice, which is obviously not correct.

Do you have some tips on how to fix this? Thanks a lot!

(BTW I know you have designed a REPL library, but because of some technical reasons I don't want to use it)

Nevermind, I found I was wrong.

Your repl was useful for me on my side projects, thanks! 😄

Hint: Lua 5.2 changes deprecated loadstring and unpack, to load and table.unpack respectively.