An interactive Lua prompt for the Textadept editor

lua_prompt.lua

-- makes interactive prompt dodgy.
-- (In an ideal world, should be able to switch this off only for
-- the message buffer)
_m.textadept.editing.AUTOPAIR = false

-- useful function which can safely handle argument lists containing nil;
-- the resulting table has n set to the real length.
local function pack (...)
    local args = {...}
    args.n = select('#',...)
    return args
end

local function eval_lua(code)
    local status,res,val,f,err,rcnt
    code,rcnt = code:gsub('^%s*=','return ')
    f,err = loadstring(code,'TMP')
    if f then
        res = pack(pcall(f)) -- capture all the results
        local n = res.n
        if not res[1] then
          err = res[2]
        elseif n > 1 and not (n==2 and res[2]==nil) then
           -- all results except the status; ignore functions returning nil
          print(unpack(res,2,n))
        end
    end
    if err then -- either run-time or compile error
        err = 'error: '..tostring(err):gsub('^%[string "TMP"%]:1:','')
        print(err) -- 2DO: format as distinctive style
    end
end

-- the message buffer does not have a filename field; we grab the last line
-- after \n and evaluate as Lua code.
local function handle_char (ch)
  if ch == 10 and not buffer.filename then
    local line_pos = buffer.current_pos
    local lineno = buffer:line_from_position(line_pos)-1
    local line = buffer:get_line(lineno)
    eval_lua(line:gsub('^> ','')) -- strip prompt
    gui.write '> '
  end
end


function lua()
  gui.write 'Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio\n> '
  print = gui.print
  events.connect('char_added',handle_char)
end

-- finding the message buffer: factored out
local function find_buffer_of_type(buffer_type)
  -- Try to find a message buffer to print to. Otherwise create one.
  local message_buffer, message_buffer_index
  local message_view, message_view_index
  for i, buffer in ipairs(_BUFFERS) do
    if buffer._type == buffer_type then
      message_buffer, message_buffer_index = buffer, i
      for j, view in ipairs(_VIEWS) do
        if view.doc_pointer == message_buffer.doc_pointer then
          message_view, message_view_index = view, j
          break
        end
      end
      break
    end
  end
  if not message_view then
    local _, message_view = view:split(false) -- horizontal split
    if not message_buffer then
      message_buffer = new_buffer()
      message_buffer._type = buffer_type
      events.emit('file_opened')
    else
      message_view:goto_buffer(message_buffer_index, true)
    end
  else
    gui.goto_view(message_view_index, true)
  end
end

-- append text to a buffer of given type, and position the caret at the end.
function gui._write(buffer_type,text)
  local function safe_write(text)
    if buffer._type ~= buffer_type then
      find_buffer_of_type(buffer_type)
    end
    buffer:append_text(text)
    buffer:goto_pos(buffer.length)
  end
  pcall(safe_write, text) -- prevent endless loops on error
end

--  gui._print is here redefined, to use _write.
-- It also uses pack() to ensure that it can handle arg lists with nils
-- and other values which are not numbers or strings (table.concat
-- will choke on these)
function gui._print(buffer_type, ...)
  local args = pack(...)
  for i = 1,args.n do
    args[i] = tostring(args[i])
  end
  gui._write(buffer_type,table.concat(args, '\t'))
  gui._write(buffer_type,'\n')
  buffer:set_save_point()
end

function gui.write(text)
  gui._write("[Message Buffer]",text)
  buffer:set_save_point()
end