def iter_macroexpand(env, source_obj, position=None):
if env:
compiler = env.get("__compiler__") or current()
elif env is None:
compiler = current()
if compiler:
env = compiler.env
if env is None:
raise CompilerException("macroexpand requires non-None env when"
" no compiler is active")
if position is None and is_pair(source_obj):
position = source_obj.get_position()
# expander = env_get_expander(env, source_obj)
expander = compiler.find_expander(source_obj, env)
while expander:
expanded = expander()
yield expanded
# expander = env_get_expander(env, expanded)
expander = compiler.find_expander(expanded, env)
if is_pair(expanded):
fill_position(expanded, position)
def iter_macroexpand(env, source_obj, position=None):
if env:
compiler = env.get("__compiler__") or current()
elif env is None:
compiler = current()
if compiler:
env = compiler.env
if env is None:
raise CompilerException("macroexpand requires non-None env when"
" no compiler is active")
if position is None and is_pair(source_obj):
position = source_obj.get_position()
# expander = env_get_expander(env, source_obj)
expander = compiler.find_expander(source_obj, env)
while expander:
expanded = expander()
yield expanded
# expander = env_get_expander(env, expanded)
expander = compiler.find_expander(expanded, env)
if is_pair(expanded):
fill_position(expanded, position)
def error(self, message, source):
"""
Create a CompilerSyntaxError based on the message and source
object. Will attempt to find position and line text based
on the compiler's state.
"""
text = None
pos = None
if is_pair(source) and source is not nil:
pos = source.get_position()
if pos and exists(self.filename):
with open(self.filename, "rt") as fin:
for text, _lineno in zip(fin, range(0, pos[0])):
# print(" ...", text)
pass
if not text:
text = str(source)
if pos:
pos = (pos[0], 0)
return CompilerSyntaxError(message, pos, text=text,
filename=self.filename)
def test_nil(self):
# singleton nil check
Nil = type(nil)
self.assertEqual(id(nil), id(Nil()))
self.assertEqual(id(Nil()), id(Nil()))
self.assertTrue(nil is Nil())
# behavior
self.assertIsInstance(nil, pair)
self.assertTrue(is_pair(nil))
self.assertTrue(is_nil(nil))
self.assertTrue(is_proper(nil))
self.assertFalse(nil)
self.assertTrue(not nil)
self.assertEqual(str(nil), "nil")
self.assertEqual(repr(nil), "nil")
self.assertEqual(nil, nil)
self.assertNotEqual(nil, cons(1, nil))
self.assertNotEqual(cons(1, nil), nil)
with self.assertRaises(TypeError):
car(nil)
with self.assertRaises(TypeError):
cdr(nil)
self.assertEqual(list(nil), list())
self.assertEqual(tuple(nil), tuple())
def compile(self, source_obj, tc, cont):
"""
Compile a supported source object into an expression.
pair, symbol, keyword, and the pythonic constant types are
valid source obj types.
"""
self.require_active()
tc = self.tco_enabled and tc
if is_pair(source_obj):
dispatch = self.compile_pair
elif is_symbol(source_obj) or is_lazygensym(source_obj):
dispatch = self.compile_symbol
elif is_keyword(source_obj):
dispatch = self.compile_keyword
elif isinstance(source_obj, CONST_TYPES):
dispatch = self.compile_constant
else:
msg = "Unsupported source object %r" % source_obj
raise CompilerException(msg)
try:
return dispatch(source_obj, tc, cont or self._compile_cont)
except (CompilerException, SibilantSyntaxError):
# these two should be propogated unchanged
raise
except Exception as ex:
raise UncaughtCompilerException(ex, source_obj)
def error(self, message, source):
"""
Create a CompilerSyntaxError based on the message and source
object. Will attempt to find position and line text based
on the compiler's state.
"""
text = None
pos = None
if is_pair(source) and source is not nil:
pos = source.get_position()
if pos and exists(self.filename):
with open(self.filename, "rt") as fin:
for text, _lineno in zip(fin, range(0, pos[0])):
# print(" ...", text)
pass
if not text:
text = str(source)
if pos:
pos = (pos[0], 0)
return CompilerSyntaxError(message,
pos,
text=text,
filename=self.filename)
def test_recursive_cons(self):
a = cons(1, 2, 3, recursive=True)
self.assertTrue(a.is_proper())
self.assertTrue(a.is_recursive())
self.assertTrue(is_pair(a))
self.assertTrue(is_proper(a))
self.assertEqual(a.length(), 3)
self.assertEqual(car(a), car(cdr(cdr(cdr(a)))))
self.assertEqual(str(a), "(1 2 3 ...)")
self.assertEqual(repr(a), "cons(1, 2, 3, recursive=True)")
b = pair(0, a)
c = pair(0, a)
self.assertEqual(b, c)
self.assertNotEqual(a, b)
self.assertNotEqual(a, c)
z = cons(1, cons(2, cons(3, nil)))
setcdr(cdr(cdr(z)), z)
self.assertEqual(a, z)
self.assertEqual(z, a)
def test_nil(self):
# singleton nil check
Nil = type(nil)
self.assertEqual(id(nil), id(Nil()))
self.assertEqual(id(Nil()), id(Nil()))
self.assertTrue(nil is Nil())
# behavior
self.assertIsInstance(nil, pair)
self.assertTrue(is_pair(nil))
self.assertTrue(is_nil(nil))
self.assertTrue(is_proper(nil))
self.assertFalse(nil)
self.assertTrue(not nil)
self.assertEqual(str(nil), "nil")
self.assertEqual(repr(nil), "nil")
self.assertEqual(nil, nil)
self.assertNotEqual(nil, cons(1, nil))
self.assertNotEqual(cons(1, nil), nil)
with self.assertRaises(TypeError):
car(nil)
with self.assertRaises(TypeError):
cdr(nil)
self.assertEqual(list(nil), list())
self.assertEqual(tuple(nil), tuple())
def test_recursive_cons(self):
a = cons(1, 2, 3, recursive=True)
self.assertTrue(a.is_proper())
self.assertTrue(a.is_recursive())
self.assertTrue(is_pair(a))
self.assertTrue(is_proper(a))
self.assertEqual(a.length(), 3)
self.assertEqual(car(a), car(cdr(cdr(cdr(a)))))
self.assertEqual(str(a), "(1 2 3 ...)")
self.assertEqual(repr(a), "cons(1, 2, 3, recursive=True)")
b = pair(0, a)
c = pair(0, a)
self.assertEqual(b, c)
self.assertNotEqual(a, b)
self.assertNotEqual(a, c)
z = cons(1, cons(2, cons(3, nil)))
setcdr(cdr(cdr(z)), z)
self.assertEqual(a, z)
self.assertEqual(z, a)
def compile(self, compiler, source_obj, tc, cont):
expanded = self.expand()
expanded = _symbol_None if expanded is None else expanded
if is_pair(source_obj):
called_by, source = source_obj
res = cons(expanded, source)
fill_position(res, source_obj.get_position())
expanded = res
return tcf(cont, expanded, tc)
def compile(self, compiler, source_obj, tc, cont):
expanded = self.expand()
expanded = _symbol_None if expanded is None else expanded
if is_pair(source_obj):
called_by, source = source_obj
res = cons(expanded, source)
fill_position(res, source_obj.get_position())
expanded = res
return tcf(cont, expanded, tc)
def compile_apply(self, source_obj: pair, tc, cont):
"""
Compile a runtime function apply expression.
"""
tc = tc and self.tco_enabled and not self.generator
head, tail = source_obj
if tc and self.self_ref and \
is_symbol(head) and (str(head) == self.name):
return tcf(self.compile_tcr_apply, source_obj, tc, cont)
pos = source_obj.get_position()
if is_pair(head):
# @trampoline
def ccp(new_head, tc):
# Continue Compiling Pair. This is how we finish
# compiling a function invocation after first
# compiling the head
if new_head is None:
# the original head pair compiled down to a None,
# which means it pushed bytecode and left a value
# on the stack. Complete the apply based on that.
return tcf(self.complete_apply, tail, pos, tc, cont)
else:
# the original head pair was transformed, so now
# we need to start over in a new compile_pair call
# using a newly assembled expression.
expr = pair(new_head, tail)
expr.set_position(pos)
return tcf(self.compile_pair, expr, tc, cont)
# we need to compile the head first, to figure out if it
# expands into a symbolic reference or something. We'll
# use ccp as a temporary continuation. Note that the
# evaluation of the head of the pair is never a tailcall
# itself, even if it would be a tailcall to apply it as a
# function afterwards.
return tcf(self.compile_pair, head, False, ccp)
elif tc:
self.declare_tailcall()
self.pseudop_get_global(_symbol_tailcall_full)
return tcf(self.complete_apply, source_obj, pos, False, cont)
else:
self.add_expression(head)
return tcf(self.complete_apply, tail, pos, tc, cont)
def compile_apply(self, source_obj: pair, tc, cont):
"""
Compile a runtime function apply expression.
"""
tc = tc and self.tco_enabled and not self.generator
head, tail = source_obj
if tc and self.self_ref and \
is_symbol(head) and (str(head) == self.name):
return tcf(self.compile_tcr_apply, source_obj, tc, cont)
pos = source_obj.get_position()
if is_pair(head):
# @trampoline
def ccp(new_head, tc):
# Continue Compiling Pair. This is how we finish
# compiling a function invocation after first
# compiling the head
if new_head is None:
# the original head pair compiled down to a None,
# which means it pushed bytecode and left a value
# on the stack. Complete the apply based on that.
return tcf(self.complete_apply, tail, pos, tc, cont)
else:
# the original head pair was transformed, so now
# we need to start over in a new compile_pair call
# using a newly assembled expression.
expr = pair(new_head, tail)
expr.set_position(pos)
return tcf(self.compile_pair, expr, tc, cont)
# we need to compile the head first, to figure out if it
# expands into a symbolic reference or something. We'll
# use ccp as a temporary continuation. Note that the
# evaluation of the head of the pair is never a tailcall
# itself, even if it would be a tailcall to apply it as a
# function afterwards.
return tcf(self.compile_pair, head, False, ccp)
elif tc:
self.declare_tailcall()
self.pseudop_get_global(_symbol_tailcall_full)
return tcf(self.complete_apply, source_obj, pos, False, cont)
else:
self.add_expression(head)
return tcf(self.complete_apply, tail, pos, tc, cont)
def test_improper_cons(self):
z = cons(1, 2)
self.assertEqual(z.length(), 2)
self.assertFalse(z.is_proper())
self.assertEqual(car(z), 1)
self.assertEqual(cdr(z), 2)
self.assertEqual(str(z), "(1 . 2)")
self.assertEqual(repr(z), "cons(1, 2)")
self.assertTrue(is_pair(z))
self.assertFalse(is_proper(z))
self.assertNotEqual(z, None)
self.assertNotEqual(z, nil)
self.assertNotEqual(z, cons(1, nil))
self.assertNotEqual(z, cons(1, 3))
self.assertNotEqual(z, cons(1, 3, nil))
def test_improper_cons(self):
z = cons(1, 2)
self.assertEqual(z.length(), 2)
self.assertFalse(z.is_proper())
self.assertEqual(car(z), 1)
self.assertEqual(cdr(z), 2)
self.assertEqual(str(z), "(1 . 2)")
self.assertEqual(repr(z), "cons(1, 2)")
self.assertTrue(is_pair(z))
self.assertFalse(is_proper(z))
self.assertNotEqual(z, None)
self.assertNotEqual(z, nil)
self.assertNotEqual(z, cons(1, nil))
self.assertNotEqual(z, cons(1, 3))
self.assertNotEqual(z, cons(1, 3, nil))
def compile_pair(self, source_obj: pair, tc, cont):
"""
Compile a pair expression. This will become either a literal nil,
a macro expansion, a special invocation, or a runtime function
application.
"""
if is_nil(source_obj):
return tcf(self.compile_nil, source_obj, tc, cont)
if not is_proper(source_obj):
# print("** WUT", self, source_obj, tc, cont)
msg = "cannot evaluate improper lists as expressions"
raise self.error(msg, source_obj)
self.pseudop_position_of(source_obj)
head, tail = source_obj
if is_symbol(head) or is_lazygensym(head):
comp = self.find_compiled(head)
if comp:
# the head of the pair is a symbolic reference which
# resolved to a compile-time object. Invoke that.
return tcf(comp.compile, self, source_obj, tc, cont)
else:
return tcf(self.compile_apply, source_obj, tc, cont)
elif is_pair(head):
return tcf(self.compile_apply, source_obj, tc, cont)
else:
# TODO: should this be a compile-time error? If we have
# something that isn't a symbolic reference or isn't a
# pair, then WTF else would it be? Let's just let it break
# at runtime, for now.
return tcf(self.compile_apply, source_obj, tc, cont)
def compile_pair(self, source_obj: pair, tc, cont):
"""
Compile a pair expression. This will become either a literal nil,
a macro expansion, a special invocation, or a runtime function
application.
"""
if is_nil(source_obj):
return tcf(self.compile_nil, source_obj, tc, cont)
if not is_proper(source_obj):
# print("** WUT", self, source_obj, tc, cont)
msg = "cannot evaluate improper lists as expressions"
raise self.error(msg, source_obj)
self.pseudop_position_of(source_obj)
head, tail = source_obj
if is_symbol(head) or is_lazygensym(head):
comp = self.find_compiled(head)
if comp:
# the head of the pair is a symbolic reference which
# resolved to a compile-time object. Invoke that.
return tcf(comp.compile, self, source_obj, tc, cont)
else:
return tcf(self.compile_apply, source_obj, tc, cont)
elif is_pair(head):
return tcf(self.compile_apply, source_obj, tc, cont)
else:
# TODO: should this be a compile-time error? If we have
# something that isn't a symbolic reference or isn't a
# pair, then WTF else would it be? Let's just let it break
# at runtime, for now.
return tcf(self.compile_apply, source_obj, tc, cont)
def compile(self, source_obj, tc, cont):
"""
Compile a supported source object into an expression.
pair, symbol, keyword, and the pythonic constant types are
valid source obj types.
"""
tc = self.tco_enabled and tc
if is_pair(source_obj):
dispatch = self.compile_pair
elif is_symbol(source_obj) or is_lazygensym(source_obj):
dispatch = self.compile_symbol
elif is_keyword(source_obj):
dispatch = self.compile_keyword
elif isinstance(source_obj, CONST_TYPES):
dispatch = self.compile_constant
else:
msg = "Unsupported source object %r" % source_obj
raise self.error(msg, source_obj)
return tcf(dispatch, source_obj, tc, cont or self._compile_cont)
def gather_formals(args, declared_at=None, filename=None):
"""
parses formals pair args into five values:
(positional, keywords, defaults, stararg, starstararg)
- positional is a list of symbols defining positional arguments
- defaults is a list of keywords and expr pairs defining keyword
arguments and their default value expression
- kwonly is a list of keywords and expr pairs which are
keyword-only arguments and theid default value expression
- stararg is a symbol for variadic positional arguments
- starstararg is a symbol for variadic keyword arguments
"""
undefined = object()
err = partial(SibilantSyntaxError, location=declared_at, filename=filename)
if is_symbol(args):
return ((), (), (), args, None)
elif isinstance(args, (list, tuple)):
improper = False
args = cons(*args, nil)
elif is_proper(args):
improper = False
elif is_pair(args):
improper = True
else:
raise err("formals must be symbol or pair, not %r" % args)
positional = []
iargs = iter(args.unpack())
for arg in iargs:
if is_keyword(arg):
if improper:
raise err("cannot mix improper formal with keywords")
else:
break
elif is_symbol(arg) or is_lazygensym(arg):
positional.append(arg)
else:
raise err("positional formals must be symbols, not %r" % arg)
else:
# handled all of args, done deal.
if improper:
return (positional[:-1], (), (), positional[-1], None)
else:
return (positional, (), (), None, None)
defaults = []
kwonly = []
while arg not in (_keyword_star, _keyword_starstar):
value = next(iargs, undefined)
if value is undefined:
raise err("missing value for keyword formal %s" % args)
else:
defaults.append((arg, value))
arg = next(iargs, undefined)
if arg is undefined:
break
elif is_keyword(arg):
continue
else:
raise err("keyword formals must be alternating keywords and"
" values, not %r" % arg)
star = None
starstar = None
if arg is undefined:
return (positional, defaults, kwonly, None, None)
if arg is _keyword_star:
star = next(iargs, undefined)
if star is undefined:
raise err("* keyword requires symbol binding")
elif star is nil:
# nil means an ignored star arg, this is allowed.
pass
elif not (is_symbol(star) or is_lazygensym(star)):
raise err("* keyword requires symbol binding, not %r" % star)
arg = next(iargs, undefined)
if arg is undefined:
return (positional, defaults, kwonly, star, starstar)
# while is_symbol(arg):
# kwonly.append(arg)
# arg = next(iargs, undefined)
#
# if arg is undefined:
# return (positional, defaults, kwonly, star, starstar)
if not is_keyword(arg):
raise err("expected keyword in formals, got %r" % arg)
# keyword formals after *: are considered keyword-only
while arg not in (_keyword_star, _keyword_starstar):
value = next(iargs, undefined)
if value is undefined:
raise err("missing value for keyword-only formal %s" % arg)
else:
kwonly.append((arg, value))
arg = next(iargs, undefined)
if arg is undefined:
break
elif is_keyword(arg):
continue
else:
raise err("keyword-only formals must be alternating keywords"
" and values, not %r" % arg)
if arg is _keyword_starstar:
starstar = next(iargs, undefined)
if starstar is undefined:
raise err("** keyword requires symbol binding")
elif not (is_symbol(starstar) or is_lazygensym(starstar)):
raise err("** keyword requires symbol binding, not %r" % star)
arg = next(iargs, undefined)
if arg is not undefined:
raise err("leftover formals %r" % arg)
return (positional, defaults, kwonly, star, starstar)
def gather_parameters(args, declared_at=None, filename=None):
"""
parses parameter args into five values:
(positional, keywords, values, stararg, starstararg)
- positional is a list of expressions for positional arguments
- keywords is a list of keywords defining keyword arguments
- values is a list of expressions defining values for keywords
- stararg is a symbol for variadic positional expression
- starstararg is a symbol for variadic keyword expression
"""
undefined = object()
def err(msg):
return SibilantSyntaxError(msg, location=declared_at,
filename=filename)
if is_symbol(args) or is_lazygensym(args):
return ((), (), (), args, None)
elif isinstance(args, (list, tuple)):
improper = False
args = cons(*args, nil) if args else nil
elif is_proper(args):
improper = False
elif is_pair(args):
improper = True
else:
raise err("parameters must be symbol or pair, not %r" % args)
positional = []
iargs = iter(args.unpack())
for arg in iargs:
if is_keyword(arg):
break
else:
positional.append(arg)
else:
# handled all of args, done deal.
if improper:
return (positional[:-1], (), (), positional[-1], None)
else:
return (positional, (), (), None, None)
keywords = []
defaults = []
while arg not in (_keyword_star, _keyword_starstar):
keywords.append(arg)
value = next(iargs, undefined)
if value is undefined:
raise err("missing value for keyword parameter %s" % arg)
else:
defaults.append(value)
arg = next(iargs, undefined)
if arg is undefined:
break
elif is_keyword(arg):
continue
else:
raise err("keyword parameters must be alternating keywords and"
" values, not %r" % arg)
star = None
starstar = None
if arg is undefined:
return (positional, keywords, defaults, None, None)
if arg is _keyword_star:
star = next(iargs, undefined)
if star is undefined:
raise err("* keyword parameter needs value")
arg = next(iargs, undefined)
if arg is _keyword_starstar:
starstar = next(iargs, undefined)
if starstar is undefined:
raise err("** keyword parameter needs value")
arg = next(iargs, undefined)
if arg is not undefined:
raise err("leftover parameters %r" % arg)
return (positional, keywords, defaults, star, starstar)
def gather_formals(args, declared_at=None, filename=None):
"""
parses formals pair args into five values:
(positional, keywords, defaults, stararg, starstararg)
- positional is a list of symbols defining positional arguments
- defaults is a list of keywords and expr pairs defining keyword
arguments and their default value expression
- kwonly is a list of keywords and expr pairs which are
keyword-only arguments and theid default value expression
- stararg is a symbol for variadic positional arguments
- starstararg is a symbol for variadic keyword arguments
"""
undefined = object()
err = partial(SibilantSyntaxError,
location=declared_at,
filename=filename)
if is_symbol(args):
return ((), (), (), args, None)
elif isinstance(args, (list, tuple)):
improper = False
args = cons(*args, nil)
elif is_proper(args):
improper = False
elif is_pair(args):
improper = True
else:
raise err("formals must be symbol or pair, not %r" % args)
positional = []
iargs = iter(args.unpack())
for arg in iargs:
if is_keyword(arg):
if improper:
raise err("cannot mix improper formal with keywords")
else:
break
elif is_symbol(arg) or is_lazygensym(arg):
positional.append(arg)
else:
raise err("positional formals must be symbols, nor %r" % arg)
else:
# handled all of args, done deal.
if improper:
return (positional[:-1], (), (), positional[-1], None)
else:
return (positional, (), (), None, None)
defaults = []
kwonly = []
while arg not in (_keyword_star, _keyword_starstar):
value = next(iargs, undefined)
if value is undefined:
raise err("missing value for keyword formal %s" % args)
else:
defaults.append((arg, value))
arg = next(iargs, undefined)
if arg is undefined:
break
elif is_keyword(arg):
continue
else:
raise err("keyword formals must be alternating keywords and"
" values, not %r" % arg)
star = None
starstar = None
if arg is undefined:
return (positional, defaults, kwonly, None, None)
if arg is _keyword_star:
star = next(iargs, undefined)
if star is undefined:
raise err("* keyword requires symbol binding")
elif star is nil:
# nil means an ignored star arg, this is allowed.
pass
elif not (is_symbol(star) or is_lazygensym(star)):
raise err("* keyword requires symbol binding, not %r" % star)
arg = next(iargs, undefined)
if arg is undefined:
return (positional, defaults, kwonly, star, starstar)
# while is_symbol(arg):
# kwonly.append(arg)
# arg = next(iargs, undefined)
#
# if arg is undefined:
# return (positional, defaults, kwonly, star, starstar)
if not is_keyword(arg):
raise err("expected keyword in formals, got %r" % arg)
# keyword formals after *: are considered keyword-only
while arg not in (_keyword_star, _keyword_starstar):
value = next(iargs, undefined)
if value is undefined:
raise err("missing value for keyword-only formal %s" % arg)
else:
kwonly.append((arg, value))
arg = next(iargs, undefined)
if arg is undefined:
break
elif is_keyword(arg):
continue
else:
raise err("keyword-only formals must be alternating keywords"
" and values, not %r" % arg)
if arg is _keyword_starstar:
starstar = next(iargs, undefined)
if starstar is undefined:
raise err("** keyword requires symbol binding")
elif not (is_symbol(starstar) or is_lazygensym(starstar)):
raise err("** keyword requires symbol binding, not %r" % star)
arg = next(iargs, undefined)
if arg is not undefined:
raise err("leftover formals %r" % arg)
return (positional, defaults, kwonly, star, starstar)
def gather_parameters(args, declared_at=None, filename=None):
"""
parses parameter args into five values:
(positional, keywords, values, stararg, starstararg)
- positional is a list of expressions for positional arguments
- keywords is a list of keywords defining keyword arguments
- values is a list of expressions defining values for keywords
- stararg is a symbol for variadic positional expression
- starstararg is a symbol for variadic keyword expression
"""
undefined = object()
def err(msg):
return SibilantSyntaxError(msg,
location=declared_at,
filename=filename)
if is_symbol(args) or is_lazygensym(args):
return ((), (), (), args, None)
elif isinstance(args, (list, tuple)):
improper = False
args = cons(*args, nil) if args else nil
elif is_proper(args):
improper = False
elif is_pair(args):
improper = True
else:
raise err("parameters must be symbol or pair, not %r" % args)
positional = []
iargs = iter(args.unpack())
for arg in iargs:
if is_keyword(arg):
break
else:
positional.append(arg)
else:
# handled all of args, done deal.
if improper:
return (positional[:-1], (), (), positional[-1], None)
else:
return (positional, (), (), None, None)
keywords = []
defaults = []
while arg not in (_keyword_star, _keyword_starstar):
keywords.append(arg)
value = next(iargs, undefined)
if value is undefined:
raise err("missing value for keyword parameter %s" % arg)
else:
defaults.append(value)
arg = next(iargs, undefined)
if arg is undefined:
break
elif is_keyword(arg):
continue
else:
raise err("keyword parameters must be alternating keywords and"
" values, not %r" % arg)
star = None
starstar = None
if arg is undefined:
return (positional, keywords, defaults, None, None)
if arg is _keyword_star:
star = next(iargs, undefined)
if star is undefined:
raise err("* keyword parameter needs value")
arg = next(iargs, undefined)
if arg is _keyword_starstar:
starstar = next(iargs, undefined)
if starstar is undefined:
raise err("** keyword parameter needs value")
arg = next(iargs, undefined)
if arg is not undefined:
raise err("leftover parameters %r" % arg)
return (positional, keywords, defaults, star, starstar)
