alias _dont        ""
alias _do          "$*"
                  
set _ifstack       ""
alias #            "$_ifstack $*"

alias #ifeq        "set _ifnew_$1 _dont; set _ifnew_$2 _do; _ifeq_2 _ifnew_$1"
alias #ifneq       "set _ifnew_$1 _do; set _ifnew_$2 _dont; _ifeq_2 _ifnew_$1"
alias _ifeq_2      "set _ifstack \"${$1} $_ifstack\""
alias #else        "_else_2$_ifstack"
alias _else_2_do   "set _ifstack \"_dont ${* q?}\""
alias _else_2_dont "set _ifstack \"_do ${* q?}\""
alias #endif       "_endif_2 $_ifstack"
alias _endif_2     "set _ifstack \"${2- q?}\""

alias #ifdef       "#ifneq \"${$1 ?}\" \"\""
alias #ifndef      "#ifeq \"${$1 ?}\" \"\""

alias #include     "# exec $*"
alias #define      "# set $*"
alias #undef       "# unset $*"
alias #error       "# echo ERROR: $*; # quit"
alias #warning     "# echo WARNING: $*"

// EXAMPLE:
//	#ifeq "$a" "$b"
//	#ifeq "$a" "$c"
//	#	echo "a == b == c"
//	#else
//	#	echo "a == b != c"
//	#endif
//	#else
//	#ifeq "$a" "$c"
//	#	echo "a == c != b"
//	#else
//	#ifeq "$b" "$c"
//	#	echo "b == c != a"
//	#else
//	#	echo "a != b != c != a"
//	#endif
//	#endif
//	#endif