&say = Seq(
	Param('$string') :: undef,
	App(
		Sym('&print') :: undef,
		Sym('$*OUT') :: undef,
		App(
			Sym('&infix:<~>') :: undef,
			Sym('$string') ::undef,
			Val("\n") :: undef,
		) :: undef,
	) :: undef,
) ::undef,

&say = Seq(
	Param('$string') :: undef,
	App(
		Val(
			Prim(
				...
			) :: (handle, str -> int)
		) :: undef,
		Val(
			\*STDOUT :: ??,
		) :: undef,
		App(
			Val(
				Prim(
					...
				) :: (str, str -> str)
			) :: undef,
			Sym('$string') ::undef,
			Val("\n") :: undef,
		) :: undef,
	) :: undef,
) ::undef,

&say = Seq(
	Param('$string') :: undef,
	App(
		Val(
			Prim(
				...
			) :: (handle, str -> int)
		) :: (handle, str -> int),
		Val(
			\*STDOUT :: handle,
		) :: handle,
		App(
			Val(
				Prim(
					...
				) :: (str, str -> str)
			) :: (str, str -> str),
			Sym('$string') ::undef,
			Val("\n") :: undef,
		) :: undef,
	) :: undef,
) ::undef,

# type propagation
&say = Seq(
	Param('$string') :: str, # enforced by Sym('$string') below
	App(
		Val(
			Prim(
				...
			) :: (handle, str -> int)
		) :: (handle, str -> int),
		Val(
			\*STDOUT :: handle,
		) :: (x -> handle) handle,
		App(
			Val(
				Prim(
					...
				) :: (str, str -> str)
			) :: (str, str -> str),
			Sym('$string') :: str,
			Val("\n") :: (x -> str) undef,
		) :: (x -> str) str, # from -> of the first arg
	) :: (undef -> int),
) :: (undef -> int),

# type unification
&say = Seq(
	Param('$string') :: str,
	App(
		Val(
			Prim(
				...
			) :: (handle, str -> int)
		) :: (handle, str -> int),
		Val(
			\*STDOUT :: handle,
		) :: (x -> handle) handle,
		App(
			Val(
				Prim(
					...
				) :: (str, str -> str)
			) :: (str, str -> str),
			Sym('$string') :: str,
			Val("\n") :: (x -> str) undef,
		) :: str
	) :: int,
) :: (str -> int),