#testmode:repl

1 2 3
1 (2) 3
1 (2,) 3
1 (2 3) 4

(1 2 3)
(1 (2) 3)
(1 (2,) 3)
(1 (2 3) 4)

1 'a' 2 3 | null
1 ('a' 2) 3 | null
1 'a' 2 3 | null
1 ('a' 2) 3 | null
1 (2 'a' 3) 4 | null
1 (2 'b' 3) 4 | null

(1 'a' 2 3) | null
(1 ('a' 2) 3) | null
(1 (2 'a' 3) 4) | null
(1 (2 'b' 3) 4) | null

#---
#a
#---

#(1, 2, 3)
#(1, 2, 3)
#(1, (2, ), 3)
#(1, (2, 3), 4)

#(1, 2, 3)
#(1, 2, 3)
#(1, (2, ), 3)
#(1, (2, 3), 4)

#(1, 2, 3)
#(1, 2, 3)
#(1, 2, 3)
#(1, 2, 3)
#(1, (2, 3), 4)
#null

#(1, 2, 3)
#(1, 2, 3)
#(1, (2, 3), 4)
#null