Redesign argument storing

* Use state objects instead of tons of locals in the main
  function.
* Use actions for storing arguments into result table.
  Actions are now called at the end of each invocation,
  with result table, target index, arguments and overwrite flag as
  arguments.
* Remove command actions.
* Improve error messages, refer to options by the last used alias
  instead of the main name.

TODO:

* Improve error messages further ("argument 'foo' is required"
  -> "missing argument 'foo'", etc.).
* Add actions for positional arguments.
* Add actions for commands (should be called with final results
  after parsing is over, in "innermost first" order).
* Allow referring to built-in actions by strings a-la Python
  (e.g. action = "store_false").
* Allow setting initial value to be stored at target index
  for each option (perhaps use default value for that).
* Add more tests, particularly for actions.

spec/actions_spec.lua

@@ -3,8 +3,14 @@ getmetatable(Parser()).error = function(_, msg) error(msg) end
 
 describe("tests related to actions", function()
    it("calls actions for options", function()
-      local action1 = spy.new(function() end)
-      local action2 = spy.new(function() end)
+      local action1 = spy.new(function(_, _, arg)
+         assert.equal("nowhere", arg)
+      end)
+      local expected_args = {"Alice", "Bob"}
+      local action2 = spy.new(function(_, _, args)
+         assert.same(expected_args, args)
+         expected_args = {"Emma", "John"}
+      end)
 
       local parser = Parser()
       parser:option "-f" "--from" {
@@ -16,8 +22,7 @@ describe("tests related to actions", function()
          args = 2
       }
 
-      local args = parser:parse{"-fnowhere", "--pair", "Alice", "Bob", "-p", "Emma", "John"}
-      assert.same({from = "nowhere", pair = {{"Alice", "Bob"}, {"Emma", "John"}}}, args)
+      parser:parse{"-fnowhere", "--pair", "Alice", "Bob", "-p", "Emma", "John"}
       assert.spy(action1).called(1)
       assert.spy(action2).called(2)
    end)
@@ -39,27 +44,9 @@ describe("tests related to actions", function()
          action = function(...) return action3(...) end
       }
 
-      local args = parser:parse{"-vv", "--quiet"}
-      assert.same({verbose = 2, quiet = true}, args)
+      parser:parse{"-vv", "--quiet"}
       assert.spy(action1).called(2)
       assert.spy(action2).called(1)
       assert.spy(action3).called(0)
    end)
-
-   it("calls actions for commands", function()
-      local action = spy.new(function() end)
-
-      local parser = Parser "name"
-      parser:flag "-v" "--verbose" {
-         count = "0-3"
-      }
-      local add = parser:command "add" {
-         action = function(...) return action(...) end
-      }
-      add:argument "something"
-
-      local args = parser:parse{"add", "me"}
-      assert.same({add = true, verbose = 0, something = "me"}, args)
-      assert.spy(action).called(1)
-   end)
 end)

spec/arguments_spec.lua

@@ -97,7 +97,7 @@ describe("tests related to positional arguments", function()
          local parser = Parser()
          parser:argument "foo"
 
-         assert.has_error(function() parser:parse{} end, "too few arguments")
+         assert.has_error(function() parser:parse{} end, "argument 'foo' is required")
       end)
 
       it("handles extra arguments with several arguments correctly", function()
@@ -113,7 +113,7 @@ describe("tests related to positional arguments", function()
          parser:argument "foo1"
          parser:argument "foo2"
 
-         assert.has_error(function() parser:parse{"bar"} end, "too few arguments")
+         assert.has_error(function() parser:parse{"bar"} end, "argument 'foo2' is required")
       end)
 
       it("handles too few arguments with multi-argument correctly", function()
@@ -121,7 +121,7 @@ describe("tests related to positional arguments", function()
          parser:argument "foo" {
             args = "+"
          }
-         assert.has_error(function() parser:parse{} end, "too few arguments")
+         assert.has_error(function() parser:parse{} end, "argument 'foo' is required")
       end)
 
       it("handles too many arguments with multi-argument correctly", function()
@@ -137,7 +137,7 @@ describe("tests related to positional arguments", function()
          parser:argument "foo" {
             args = "2-4"
          }
-         assert.has_error(function() parser:parse{"foo"} end, "too few arguments")
+         assert.has_error(function() parser:parse{"foo"} end, "argument 'foo' requires at least 2 arguments")
       end)
 
       it("handles too many arguments with several multi-arguments correctly", function()
@@ -159,7 +159,7 @@ describe("tests related to positional arguments", function()
          parser:argument "foo2" {
             args = "*"
          }
-         assert.has_error(function() parser:parse{} end, "too few arguments")
+         assert.has_error(function() parser:parse{} end, "argument 'foo1' is required")
       end)
    end)
 end)

spec/default_spec.lua

@@ -55,7 +55,7 @@ describe("tests related to default values", function()
          assert.same({output = "a.out"}, args)
          args = parser:parse{"--output", "foo.txt"}
          assert.same({output = "foo.txt"}, args)
-         assert.has_error(function() parser:parse{"-o"} end, "too few arguments")
+         assert.has_error(function() parser:parse{"-o"} end, "option '-o' requires an argument")
       end)
 
       it("handles option with default value for multi-argument option correctly", function()

spec/integrity_spec.lua

@@ -20,7 +20,7 @@ describe("tests related to CLI behaviour #unsafe", function()
          assert.equal([[
 Usage: ]]..script..[[ [-v] [-h] <input> [<command>] ...
 
-Error: too few arguments
+Error: argument 'input' is required
 ]], get_output(""))
       end)
 
@@ -62,7 +62,7 @@ Did you mean 'install'?
          assert.equal([[
 Usage: ]]..script..[[ install [-f <from>] [-h] <rock> [<version>]
 
-Error: too few arguments
+Error: argument 'rock' is required
 ]], get_output("foo install"))
       end)
 

spec/options_spec.lua

@@ -258,7 +258,8 @@ describe("tests related to options", function()
       it("handles lack of required argument correctly", function()
          local parser = Parser()
          parser:option "-s" "--server"
-         assert.has_error(function() parser:parse{"--server"} end, "too few arguments")
+         assert.has_error(function() parser:parse{"--server"} end, "option '--server' requires an argument")
+         assert.has_error(function() parser:parse{"-s"} end, "option '-s' requires an argument")
       end)
 
       it("handles unknown options correctly", function()
@@ -289,7 +290,7 @@ describe("tests related to options", function()
             count = 1,
             overwrite = false
          }
-         assert.has_error(function() parser:parse{"-qq"} end, "option '-q' must be used at most 1 time")
+         assert.has_error(function() parser:parse{"-qq"} end, "option '-q' must be used 1 time")
       end)
 
       it("handles too few invocations correctly", function()

spec/pparse_spec.lua

@@ -15,13 +15,13 @@ describe("tests related to :pparse()", function()
       parser:argument "foo"
       local ok, errmsg = parser:pparse{}
       assert.is_false(ok)
-      assert.equal("too few arguments", errmsg)
+      assert.equal("argument 'foo' is required", errmsg)
    end)
 
-   it("still raises an error if it is caused by misconfiguration", function()
+   it("rethrows errors from callbacks", function()
       local parser = Parser()
       parser:flag "--foo"
-         :action(error)
-      assert.has_error(function() parser:pparse{"--foo"} end)
+         :action(function() error("some error message") end)
+      assert.error_matches(function() parser:pparse{"--foo"} end, "some error message")
    end)
 end)

src/argparse.lua

@@ -19,7 +19,6 @@
 -- IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 -- CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
-
 local function deep_update(t1, t2)
    for k, v in pairs(t2) do
       if type(v) == "table" then
@@ -35,24 +34,25 @@ end
 -- A property is a tuple {name, callback}.
 -- properties.args is number of properties that can be set as arguments
 -- when calling an object.
-local function new_class(prototype, properties, parent)
+local function class(prototype, properties, parent)
    -- Class is the metatable of its instances.
-   local class = {}
-   class.__index = class
+   local cl = {}
+   cl.__index = cl
 
    if parent then
-      class.__prototype = deep_update(deep_update({}, parent.__prototype), prototype)
+      cl.__prototype = deep_update(deep_update({}, parent.__prototype), prototype)
    else
-      class.__prototype = prototype
+      cl.__prototype = prototype
    end
 
+   if properties then
       local names = {}
 
       -- Create setter methods and fill set of property names. 
       for _, property in ipairs(properties) do
          local name, callback = property[1], property[2]
 
-      class[name] = function(self, value)
+         cl[name] = function(self, value)
             if not callback(self, value) then
                self["_" .. name] = value
             end
@@ -63,7 +63,7 @@ local function new_class(prototype, properties, parent)
          names[name] = true
       end
 
-   function class.__call(self, ...)
+      function cl.__call(self, ...)
          -- When calling an object, if the first argument is a table,
          -- interpret keys as property names, else delegate arguments
          -- to corresponding setters in order.
@@ -91,6 +91,7 @@ local function new_class(prototype, properties, parent)
 
          return self
       end
+   end
 
    -- If indexing class fails, fallback to its parent.
    local class_metatable = {}
@@ -104,7 +105,7 @@ local function new_class(prototype, properties, parent)
       return object(...)
    end
 
-   return setmetatable(class, class_metatable)
+   return setmetatable(cl, class_metatable)
 end
 
 local function typecheck(name, types, value)
@@ -204,7 +205,7 @@ local add_help = {"add_help", function(self, value)
    end
 end}
 
-local Parser = new_class({
+local Parser = class({
    _arguments = {},
    _options = {},
    _commands = {},
@@ -223,7 +224,7 @@ local Parser = new_class({
    add_help
 })
 
-local Command = new_class({
+local Command = class({
    _aliases = {}
 }, {
    args = 3,
@@ -235,11 +236,10 @@ local Command = new_class({
    typechecked("help", "string"),
    typechecked("require_command", "boolean"),
    typechecked("handle_options", "boolean"),
-   typechecked("action", "function"),
    add_help
 }, Parser)
 
-local Argument = new_class({
+local Argument = class({
    _minargs = 1,
    _maxargs = 1,
    _mincount = 1,
@@ -259,7 +259,7 @@ local Argument = new_class({
    typechecked("argname", "string", "table")
 })
 
-local Option = new_class({
+local Option = class({
    _aliases = {},
    _mincount = 0,
    _overwrite = true
@@ -322,22 +322,42 @@ function Argument:_get_usage()
    return usage
 end
 
-function Argument:_get_type()
+local actions = {}
+
+function actions.store_true(result, target)
+   result[target] = true
+end
+
+function actions.store(result, target, argument)
+   result[target] = argument
+end
+
+function actions.count(result, target, _, overwrite)
+   if not overwrite then
+      result[target] = result[target] + 1
+   end
+end
+
+function actions.append(result, target, argument, overwrite)
+   table.insert(result[target], argument)
+
+   if overwrite then
+      table.remove(result[target], 1)
+   end
+end
+
+function Argument:_get_action()
    if self._maxcount == 1 then
       if self._maxargs == 0 then
-         return "flag"
-      elseif self._maxargs == 1 and (self._minargs == 1 or self._mincount == 1) then
-         return "arg"
+         return self._action or actions.store_true, nil
       else
-         return "multiarg"
+         return self._action or actions.store, nil
       end
    else
       if self._maxargs == 0 then
-         return "counter"
-      elseif self._maxargs == 1 and self._minargs == 1 then
-         return "multicount"
+         return self._action or actions.count, 0
       else
-         return "twodimensional"
+         return self._action or actions.append, {}
       end
    end
 end
@@ -411,6 +431,10 @@ function Option:_get_usage()
    return usage
 end
 
+function Argument:_get_default_target()
+   return self._name
+end
+
 function Option:_get_default_target()
    local res
 
@@ -635,8 +659,9 @@ local function get_tip(context, wrong_name)
    local possible_names = {}
 
    for name in pairs(context) do
-      for i=1, #name do
-         possible_name = name:sub(1, i-1) .. name:sub(i+1)
+      if type(name) == "string" then
+         for i = 1, #name do
+            possible_name = name:sub(1, i - 1) .. name:sub(i + 1)
 
             if not context_pool[possible_name] then
                context_pool[possible_name] = {}
@@ -645,9 +670,10 @@ local function get_tip(context, wrong_name)
             table.insert(context_pool[possible_name], name)
          end
       end
+   end
 
-   for i=1, #wrong_name+1 do
-      possible_name = wrong_name:sub(1, i-1) .. wrong_name:sub(i+1)
+   for i = 1, #wrong_name + 1 do
+      possible_name = wrong_name:sub(1, i - 1) .. wrong_name:sub(i + 1)
 
       if context[possible_name] then
          possible_names[possible_name] = true
@@ -659,6 +685,7 @@ local function get_tip(context, wrong_name)
    end
 
    local first = next(possible_names)
+
    if first then
       if next(possible_names, first) then
          local possible_names_arr = {}
@@ -677,294 +704,345 @@ local function get_tip(context, wrong_name)
    end
 end
 
-local function plural(x)
-   if x == 1 then
-      return ""
-   end
+local ElementState = class({
+   invocations = 0
+})
 
-   return "s"
+function ElementState:__call(state, element)
+   self.state = state
+   self.result = state.result
+   self.element = element
+   self.target = element._target or element:_get_default_target()
+   self.action, self.result[self.target] = element:_get_action()
+   return self
 end
 
--- Compatibility with strict.lua and other checkers:
-local default_cmdline = rawget(_G, "arg") or {}
+function ElementState:error(fmt, ...)
+   self.state:error(fmt, ...)
+end
 
-function Parser:_parse(args, errhandler)
-   args = args or default_cmdline
-   local parser
-   local charset
-   local options = {}
-   local arguments = {}
-   local commands
-   local option_mutexes = {}
-   local used_mutexes = {}
-   local opt_context = {}
-   local com_context
-   local result = {}
-   local invocations = {}
-   local passed = {}
-   local cur_option
-   local cur_arg_i = 1
-   local cur_arg
-   local targets = {}
-   local handle_options = true
+function ElementState:convert(argument)
+   local converter = self.element._convert
 
-   local function error_(fmt, ...)
-      return errhandler(parser, fmt:format(...))
-   end
-
-   local function assert_(assertion, ...)
-      return assertion or error_(...)
-   end
-
-   local function convert(element, data)
-      if element._convert then
+   if converter then
       local ok, err
 
-         if type(element._convert) == "function" then
-            ok, err = element._convert(data)
+      if type(converter) == "function" then
+         ok, err = converter(argument)
       else
-            ok = element._convert[data]
+         ok = converter[argument]
       end
 
-         assert_(ok ~= nil, "%s", err or "malformed argument '" .. data .. "'")
-         data = ok
+      if ok == nil then
+         self:error(err and "%s" or "malformed argument '%s'", err or argument)
       end
 
-      return data
+      argument = ok
    end
 
-   local invoke, pass, close
+   return argument
+end
 
-   function invoke(element)
-      local overwrite = false
+function ElementState:default(mode)
+   return self.element._defmode:find(mode) and self.element._default
+end
 
-      if invocations[element] == element._maxcount then
-         if element._overwrite then
-            overwrite = true
+local function bound(noun, min, max, is_max)
+   local res = ""
+
+   if min ~= max then
+      res = "at " .. (is_max and "most" or "least") .. " "
+   end
+
+   local number = is_max and max or min
+   return res .. tostring(number) .. " " .. noun ..  (number == 1 and "" or "s")
+end
+
+function ElementState:invoke(alias)
+   self.open = true
+   self.name = ("%s '%s'"):format(alias and "option" or "argument", alias or self.element._name)
+   self.overwrite = false
+
+   if self.invocations >= self.element._maxcount then
+      if self.element._overwrite then
+         self.overwrite = true
       else
-            error_("option '%s' must be used at most %d time%s", element._name, element._maxcount, plural(element._maxcount))
+         self:error("%s must be used %s", self.name, bound("time", self.element._mincount, self.element._maxcount, true))
       end
    else
-         invocations[element] = invocations[element]+1
+      self.invocations = self.invocations + 1
    end
 
-      passed[element] = 0
-      local type_ = element:_get_type()
-      local target = targets[element]
+   self.args = {}
 
-      if type_ == "flag" then
-         result[target] = true
-      elseif type_ == "multiarg" then
-         result[target] = {}
-      elseif type_ == "counter" then
-         if not overwrite then
-            result[target] = result[target]+1
-         end
-      elseif type_ == "multicount" then
-         if overwrite then
-            table.remove(result[target], 1)
-         end
-      elseif type_ == "twodimensional" then
-         table.insert(result[target], {})
-
-         if overwrite then
-            table.remove(result[target], 1)
-         end
+   if self.element._maxargs <= 0 then
+      self:close()
    end
 
-      if element._maxargs == 0 then
-         close(element)
-      end
+   return self.open
+end
+
+function ElementState:pass(argument)
+   argument = self:convert(argument)
+   table.insert(self.args, argument)
+
+   if #self.args >= self.element._maxargs then
+      self:close()
    end
 
-   function pass(element, data)
-      passed[element] = passed[element]+1
-      data = convert(element, data)
-      local type_ = element:_get_type()
-      local target = targets[element]
+   return self.open
+end
 
-      if type_ == "arg" then
-         result[target] = data
-      elseif type_ == "multiarg" or type_ == "multicount" then
-         table.insert(result[target], data)
-      elseif type_ == "twodimensional" then
-         table.insert(result[target][#result[target]], data)
+function ElementState:complete_invocation()
+   while #self.args < self.element._minargs do
+      self:pass(self.element._default)
    end
+end
 
-      if passed[element] == element._maxargs then
-         close(element)
-      end
-   end
+function ElementState:close()
+   if self.open then
+      self.open = false
 
-   local function complete_invocation(element)
-      while passed[element] < element._minargs do
-         pass(element, element._default)
-      end
-   end
-
-   function close(element)
-      if passed[element] < element._minargs then
-         if element._default and element._defmode:find "a" then
-            complete_invocation(element)
+      if #self.args < self.element._minargs then
+         if self:default("a") then
+            self:complete_invocation()
          else
-            error_("too few arguments")
-         end
-      else
-         if element == cur_option then
-            cur_option = nil
-         elseif element == cur_arg then
-            cur_arg_i = cur_arg_i+1
-            cur_arg = arguments[cur_arg_i]
-         end
+            if #self.args == 0 then
+               if getmetatable(self.element) == Argument then
+                  self:error("%s is required", self.name)
+               elseif self.element._maxargs == 1 then
+                  self:error("%s requires an argument", self.name)
                end
             end
 
-   local function switch(p)
-      parser = p
+            self:error("%s requires %s", self.name, bound("argument", self.element._minargs, self.element._maxargs))
+         end
+      end
+
+      local args = self.args
+
+      if self.element._maxargs <= 1 then
+         args = args[1]
+      end
+
+      if self.element._maxargs == 1 and self.element._minargs == 0 and self.element._mincount ~= self.element._maxcount then
+         args = self.args
+      end
+
+      self.action(self.result, self.target, args, self.overwrite)
+   end
+end
+
+local ParseState = class({
+   result = {},
+   options = {},
+   arguments = {},
+   argument_i = 1,
+   element_to_mutexes = {},
+   mutex_to_used_option = {}
+})
+
+function ParseState:__call(parser, error_handler)
+   self.parser = parser
+   self.error_handler = error_handler
+   self.charset = parser:_update_charset()
+   self:switch(parser)
+   return self
+end
+
+function ParseState:error(fmt, ...)
+   self.error_handler(self.parser, fmt:format(...))
+end
+
+function ParseState:switch(parser)
+   self.parser = parser
 
    for _, option in ipairs(parser._options) do
-         table.insert(options, option)
+      option = ElementState(self, option)
+      table.insert(self.options, option)
 
-         for _, alias in ipairs(option._aliases) do
-            opt_context[alias] = option
+      for _, alias in ipairs(option.element._aliases) do
+         self.options[alias] = option
       end
-
-         local type_ = option:_get_type()
-         targets[option] = option._target or option:_get_default_target()
-
-         if type_ == "counter" then
-            result[targets[option]] = 0
-         elseif type_ == "multicount" or type_ == "twodimensional" then
-            result[targets[option]] = {}
-         end
-
-         invocations[option] = 0
    end
 
    for _, mutex in ipairs(parser._mutexes) do
       for _, option in ipairs(mutex) do
-            if not option_mutexes[option] then
-               option_mutexes[option] = {mutex}
-            else
-               table.insert(option_mutexes[option], mutex)
+         if not self.element_to_mutexes[option] then
+            self.element_to_mutexes[option] = {}
          end
+
+         table.insert(self.element_to_mutexes[option], mutex)
       end
    end
 
    for _, argument in ipairs(parser._arguments) do
-         table.insert(arguments, argument)
-         invocations[argument] = 0
-         targets[argument] = argument._target or argument._name
-         invoke(argument)
+      argument = ElementState(self, argument)
+      table.insert(self.arguments, argument)
+      argument:invoke()
    end
 
-      handle_options = parser._handle_options
-      cur_arg = arguments[cur_arg_i]
-      commands = parser._commands
-      com_context = {}
-
-      for _, command in ipairs(commands) do
-         targets[command] = command._target or command._name
+   self.handle_options = parser._handle_options
+   self.argument = self.arguments[self.argument_i]
+   self.commands = parser._commands
 
+   for _, command in ipairs(self.commands) do
       for _, alias in ipairs(command._aliases) do
-            com_context[alias] = command
-         end
+         self.commands[alias] = command
       end
    end
+end
 
-   local function get_option(name)
-      return assert_(opt_context[name], "unknown option '%s'%s", name, get_tip(opt_context, name))
-   end
+function ParseState:get_option(name)
+   local option = self.options[name]
 
-   local function do_action(element)
-      if element._action then
-         element._action()
-      end
-   end
-
-   local function handle_argument(data)
-      if cur_option then
-         pass(cur_option, data)
-      elseif cur_arg then
-         pass(cur_arg, data)
+   if not option then
+      self:error("unknown option '%s'%s", name, get_tip(self.options, name))
    else
-         local com = com_context[data]
+      return option
+   end
+end
 
-         if not com then
-            if #commands > 0 then
-               error_("unknown command '%s'%s", data, get_tip(com_context, data))
+function ParseState:get_command(name)
+   local command = self.commands[name]
+
+   if not command then
+      if #self.commands > 0 then
+         self:error("unknown command '%s'%s", name, get_tip(self.commands, name))
       else
-               error_("too many arguments")
+         self:error("too many arguments")
       end
    else
-            result[targets[com]] = true
-            do_action(com)
-            switch(com)
-         end
-      end
+      return command
    end
+end
 
-   local function handle_option(data)
-      if cur_option then
-         close(cur_option)
-      end
+function ParseState:invoke(option, name)
+   self:close()
 
-      cur_option = opt_context[data]
+   if self.element_to_mutexes[option.element] then
+      for _, mutex in ipairs(self.element_to_mutexes[option.element]) do
+         local used_option = self.mutex_to_used_option[mutex]
 
-      if option_mutexes[cur_option] then
-         for _, mutex in ipairs(option_mutexes[cur_option]) do
-            if used_mutexes[mutex] and used_mutexes[mutex] ~= cur_option then
-               error_("option '%s' can not be used together with option '%s'", data, used_mutexes[mutex]._name)
+         if used_option and used_option ~= option then
+            self:error("option '%s' can not be used together with %s", name, used_option.name)
          else
-               used_mutexes[mutex] = cur_option
+            self.mutex_to_used_option[mutex] = option
          end
       end
    end
 
-      do_action(cur_option)
-      invoke(cur_option)
+   if option:invoke(name) then
+      self.option = option
+   end
+end
+
+function ParseState:pass(arg)
+   if self.option then
+      if not self.option:pass(arg) then
+         self.option = nil
+      end
+   elseif self.argument then
+      if not self.argument:pass(arg) then
+         self.argument_i = self.argument_i + 1
+         self.argument = self.arguments[self.argument_i]
+      end
+   else
+      local command = self:get_command(arg)
+      self.result[command._target or command._name] = true
+      self:switch(command)
+   end
+end
+
+function ParseState:close()
+   if self.option then
+      self.option:close()
+      self.option = nil
+   end
+end
+
+function ParseState:finalize()
+   self:close()
+
+   for i = self.argument_i, #self.arguments do
+      local argument = self.arguments[i]
+      if #argument.args == 0 and argument:default("u") then
+         argument:complete_invocation()
+      else
+         argument:close()
+      end
    end
 
-   local function mainloop()
+   if self.parser._require_command and #self.commands > 0 then
+      self:error("a command is required")
+   end
 
-      for _, data in ipairs(args) do
+   for _, option in ipairs(self.options) do
+      local name = option.name or ("option '%s'"):format(option.element._name)
+
+      if option.invocations == 0 then
+         if option:default("u") then
+            option:invoke(name)
+            option:complete_invocation()
+            option:close()
+         end
+      end
+
+      local mincount = option.element._mincount
+
+      if option.invocations < mincount then
+         if option:default("a") then
+            while option.invocations < mincount do
+               option:invoke(name)
+               option:close()
+            end
+         else
+            self:error("%s must be used %s", name, bound("time", mincount, option.element._maxcount))
+         end
+      end
+   end
+end
+
+function ParseState:parse(args)
+   for _, arg in ipairs(args) do
       local plain = true
-         local first, name, option
 
-         if handle_options then
-            first = data:sub(1, 1)
-            if charset[first] then
-               if #data > 1 then
+      if self.handle_options then
+         local first = arg:sub(1, 1)
+
+         if self.charset[first] then
+            if #arg > 1 then
                plain = false
-                  if data:sub(2, 2) == first then
-                     if #data == 2 then
-                        if cur_option then
-                           close(cur_option)
+
+               if arg:sub(2, 2) == first then
+                  if #arg == 2 then
+                     self:close()
+                     self.handle_options = false
+                  else
+                     local equals = arg:find "="
+                     if equals then
+                        local name = arg:sub(1, equals - 1)
+                        local option = self:get_option(name)
+
+                        if option.element._maxargs <= 0 then
+                           self:error("option '%s' does not take arguments", name)
                         end
 
-                        handle_options = false
+                        self:invoke(option, name)
+                        self:pass(arg:sub(equals + 1))
                      else
-                        local equal = data:find "="
-                        if equal then
-                           name = data:sub(1, equal-1)
-                           option = get_option(name)
-                           assert_(option._maxargs > 0, "option '%s' does not take arguments", name)
-
-                           handle_option(data:sub(1, equal-1))
-                           handle_argument(data:sub(equal+1))
-                        else
-                           get_option(data)
-                           handle_option(data)
+                        local option = self:get_option(arg)
+                        self:invoke(option, arg)
                      end
                   end
                else
-                     for i = 2, #data do
-                        name = first .. data:sub(i, i)
-                        option = get_option(name)
-                        handle_option(name)
+                  for i = 2, #arg do
+                     local name = first .. arg:sub(i, i)
+                     local option = self:get_option(name)
+                     self:invoke(option, name)
 
-                        if i ~= #data and option._minargs > 0 then
-                           handle_argument(data:sub(i+1))
+                     if i ~= #arg and option.element._minargs > 0 and option.element._maxargs > 0 then
+                        self:pass(arg:sub(i + 1))
                         break
                      end
                   end
@@ -974,53 +1052,12 @@ function Parser:_parse(args, errhandler)
       end
 
       if plain then
-            handle_argument(data)
-         end
-      end
-   end
-
-   switch(self)
-   charset = parser:_update_charset()
-   mainloop()
-
-   if cur_option then
-      close(cur_option)
-   end
-
-   while cur_arg do
-      if passed[cur_arg] == 0 and cur_arg._default and cur_arg._defmode:find "u" then
-         complete_invocation(cur_arg)
-      else
-         close(cur_arg)
+         self:pass(arg)
       end
    end
 
-   if parser._require_command and #commands > 0 then
-      error_("a command is required")
-   end
-
-   for _, option in ipairs(options) do
-      if invocations[option] == 0 then
-         if option._default and option._defmode:find "u" then
-            invoke(option)
-            complete_invocation(option)
-            close(option)
-         end
-      end
-
-      if invocations[option] < option._mincount then
-         if option._default and option._defmode:find "a" then
-            while invocations[option] < option._mincount do
-               invoke(option)
-               close(option)
-            end
-         else
-            error_("option '%s' must be used at least %d time%s", option._name, option._mincount, plural(option._mincount))
-         end
-      end
-   end
-
-   return result
+   self:finalize()
+   return self.result
 end
 
 function Parser:error(msg)
@@ -1028,24 +1065,37 @@ function Parser:error(msg)
    os.exit(1)
 end
 
+-- Compatibility with strict.lua and other checkers:
+local default_cmdline = rawget(_G, "arg") or {}
+
+function Parser:_parse(args, error_handler)
+   return ParseState(self, error_handler):parse(args or default_cmdline)
+end
+
 function Parser:parse(args)
-   return self:_parse(args, Parser.error)
+   return self:_parse(args, self.error)
+end
+
+local function xpcall_error_handler(err)
+   return tostring(err) .. "\noriginal " .. debug.traceback("", 2):sub(2)
 end
 
 function Parser:pparse(args)
-   local errmsg
-   local ok, result = pcall(function()
+   local parse_error
+
+   local ok, result = xpcall(function()
       return self:_parse(args, function(_, err)
-         errmsg = err
-         return error()
-      end)
+         parse_error = err
+         error(err, 0)
       end)
+   end, xpcall_error_handler)
 
    if ok then
       return true, result
+   elseif not parse_error then
+      error(result, 0)
    else
-      assert(errmsg, result)
-      return false, errmsg
+      return false, parse_error
    end
 end