====================
conditional modifier
====================

foo if bar
return if false
return true if foo
return nil if foo

---

(program
  (if_modifier (identifier) (identifier))
  (if_modifier (return) (false))
  (if_modifier (return (argument_list (true))) (identifier))
  (if_modifier (return (argument_list (nil))) (identifier)))

==============
while modifier
==============

foo while bar

---

(program (while_modifier (identifier) (identifier)))

===============
unless modifier
===============

foo unless bar

---

(program (unless_modifier (identifier) (identifier)))

==============
until modifier
==============

foo until bar

---

(program (until_modifier (identifier) (identifier)))

========
alias
========

alias :foo :bar
alias foo bar
alias $FOO $&
alias foo +

---

(program
  (alias (symbol) (symbol))
  (alias (identifier) (identifier))
  (alias (global_variable) (global_variable))
  (alias (identifier) (operator)))

========
undef
========

undef :foo
undef foo
undef +
undef :foo, :bar

---

(program
  (undef (symbol))
  (undef (identifier))
  (undef (operator))
  (undef (symbol) (symbol)))
