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type 'a buffer =
| B0
| B1 of 'a
| B2 of 'a * 'a
| B3 of 'a * 'a * 'a
let empty =
B0
let[@inline] length b =
match b with
| B0 -> 0
| B1 _ -> 1
| B2 _ -> 2
| B3 _ -> 3
let[@inline] is_empty b =
match b with
| B0 -> true
| _ -> false
let[@inline] push x0 b =
match b with
| B0 ->
B1 x0
| B1 x1 ->
B2 (x0, x1)
| B2 (x1, x2) ->
B3 (x0, x1, x2)
| B3 _ ->
assert false
let[@inline] pop b =
match b with
| B0 ->
assert false
| B1 x0 ->
x0, B0
| B2 (x0, x1) ->
x0, B1 x1
| B3 (x0, x1, x2) ->
x0, B2 (x1, x2)
let[@inline] first b =
match b with
| B0 ->
assert false
| B1 x0 ->
x0
| B2 (x0, _) ->
x0
| B3 (x0, _, _) ->
x0
let[@inline] inject b x0 =
match b with
| B0 ->
B1 x0
| B1 x1 ->
B2 (x1, x0)
| B2 (x2, x1) ->
B3 (x2, x1, x0)
| B3 _ ->
assert false
let[@inline] eject b =
match b with
| B0 ->
assert false
| B1 (x0) ->
B0, x0
| B2 (x0, x1) ->
B1 (x0), x1
| B3 (x0, x1, x2) ->
B2 (x0, x1), x2
let[@inline] last b =
match b with
| B0 ->
assert false
| B1 (x0) ->
x0
| B2 (_, x1) ->
x1
| B3 (_, _, x2) ->
x2
let[@inline] pop2 b =
match b with
| B3 (x0, x1, x2) ->
x0, x1, B1 x2
| _ ->
assert false
let[@inline] eject2 b =
match b with
| B3 (x0, x1, x2) ->
B1 x0, x1, x2
| _ ->
assert false
let[@inline] map f b =
match b with
| B0 ->
B0
| B1 (x0) ->
B1 (f x0)
| B2 (x0, x1) ->
B2 (f x0, f x1)
| B3 (x0, x1, x2) ->
B3 (f x0, f x1, f x2)
let[@inline] fold_left f accu b =
match b with
| B0 ->
accu
| B1 (x0) ->
let accu = f accu x0 in
accu
| B2 (x0, x1) ->
let accu = f accu x0 in
let accu = f accu x1 in
accu
| B3 (x0, x1, x2) ->
let accu = f accu x0 in
let accu = f accu x1 in
let accu = f accu x2 in
accu
let[@inline] fold_right f b accu =
match b with
| B0 ->
accu
| B1 (x0) ->
let accu = f x0 accu in
accu
| B2 (x0, x1) ->
let accu = f x1 accu in
let accu = f x0 accu in
accu
| B3 (x0, x1, x2) ->
let accu = f x2 accu in
let accu = f x1 accu in
let accu = f x0 accu in
accu