val fmt_list:
    (Format.formatter -> 'a -> unit) -> Format.formatter -> 'a list -> unit

val fmt_var: Format.formatter -> Atom.atom -> unit
val fmt_vars: Format.formatter -> Atom.atom list -> unit

val fmt_op: Format.formatter -> Tail.binop -> unit

val fmt_val: Format.formatter -> Tail.value -> unit
val fmt_vals: Format.formatter -> Tail.value list -> unit

val fmt_self: Format.formatter -> Tail.self -> unit