iter/sequence.mli

(*
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(** {1 Simple and Efficient Iterators} *)

(** The iterators are designed to allow easy transfer (mappings) between data
    structures, without defining [n^2] conversions between the [n] types. The
    implementation relies on the assumption that a sequence can be iterated
    on as many times as needed; this choice allows for high performance
    of many combinators. However, for transient iterators, the {!persistent}
    function is provided, storing elements of a transient iterator
    in memory; the iterator can then be used several times (See further).

    Note that some combinators also return sequences (e.g. {!group}). The
    transformation is computed on the fly every time one iterates over
    the resulting sequence. If a transformation performs heavy computation,
    {!persistent} can also be used as intermediate storage.

    Most functions are {b lazy}, i.e. they do not actually use their arguments
    until their result is iterated on. For instance, if one calls {!map}
    on a sequence, one gets a new sequence, but nothing else happens until
    this new sequence is used (by folding or iterating on it).

    If a sequence is built from an iteration function that is {b repeatable}
    (i.e. calling it several times always iterates on the same set of
    elements, for instance List.iter or Map.iter), then
    the resulting {!t} object is also repeatable. For {b one-time iter functions}
    such as iteration on a file descriptor or a {!Stream},
    the {!persistent} function can be used to iterate and store elements in
    a memory structure; the result is a sequence that iterates on the elements
    of this memory structure, cheaply and repeatably. *)

type +'a t = ('a -> unit) -> unit
  (** A sequence of values of type ['a]. If you give it a function ['a -> unit]
      it will be applied to every element of the sequence successively. *)

type +'a sequence = 'a t

type (+'a, +'b) t2 = ('a -> 'b -> unit) -> unit
  (** Sequence of pairs of values of type ['a] and ['b]. *)

(** {2 Build a sequence} *)

val from_iter : (('a -> unit) -> unit) -> 'a t
  (** Build a sequence from a iter function *)

val from_fun : (unit -> 'a option) -> 'a t
  (** Call the function repeatedly until it returns None. This
      sequence is transient, use {!persistent} if needed! *)

val empty : 'a t
  (** Empty sequence. It contains no element. *)

val singleton : 'a -> 'a t
  (** Singleton sequence, with exactly one element. *)

val doubleton : 'a -> 'a -> 'a t
  (** Sequence with exactly two elements *)

val cons : 'a -> 'a t -> 'a t
  (** [cons x l] yields [x], then yields from [l].
      Same as [append (singleton x) l] *)

val snoc : 'a t -> 'a -> 'a t
  (** Same as {!cons} but yields the element after iterating on [l] *)

val return : 'a -> 'a t
  (** Synonym to {!singleton} *)

val pure : 'a -> 'a t
  (** Synonym to {!singleton} *)

val repeat : 'a -> 'a t
  (** Infinite sequence of the same element. You may want to look
      at {!take} and the likes if you iterate on it. *)

val iterate : ('a -> 'a) -> 'a -> 'a t
  (** [iterate f x] is the infinite sequence [x, f(x), f(f(x)), ...] *)

val forever : (unit -> 'b) -> 'b t
  (** Sequence that calls the given function to produce elements.
      The sequence may be transient (depending on the function), and definitely
      is infinite. You may want to use {!take} and {!persistent}. *)

val cycle : 'a t -> 'a t
  (** Cycle forever through the given sequence. Assume the given sequence can
      be traversed any amount of times (not transient).  This yields an
      infinite sequence, you should use something like {!take} not to loop
      forever. *)

(** {2 Consume a sequence} *)

val iter : ('a -> unit) -> 'a t -> unit
  (** Consume the sequence, passing all its arguments to the function.
      Basically [iter f seq] is just [seq f]. *)

val iteri : (int -> 'a -> unit) -> 'a t -> unit
  (** Iterate on elements and their index in the sequence *)

val fold : ('a -> 'b -> 'a) -> 'a -> 'b t -> 'a
  (** Fold over elements of the sequence, consuming it *)

val foldi : ('a -> int -> 'b -> 'a) -> 'a -> 'b t -> 'a
  (** Fold over elements of the sequence and their index, consuming it *)

val map : ('a -> 'b) -> 'a t -> 'b t
  (** Map objects of the sequence into other elements, lazily *)

val mapi : (int -> 'a -> 'b) -> 'a t -> 'b t
  (** Map objects, along with their index in the sequence *)

val for_all : ('a -> bool) -> 'a t -> bool
  (** Do all elements satisfy the predicate? *)

val exists : ('a -> bool) -> 'a t -> bool
  (** Exists there some element satisfying the predicate? *)

val mem : ?eq:('a -> 'a -> bool) -> 'a -> 'a t -> bool
  (** Is the value a member of the sequence?
      @param eq the equality predicate to use (default [(=)])
      @since 0.5 *)

val find : ('a -> 'b option) -> 'a t -> 'b option
  (** Find the first element on which the function doesn't return [None]
      @since 0.5 *)

val length : 'a t -> int
  (** How long is the sequence? Forces the sequence. *)

val is_empty : 'a t -> bool
  (** Is the sequence empty? Forces the sequence. *)

(** {2 Transform a sequence} *)

val filter : ('a -> bool) -> 'a t -> 'a t
  (** Filter on elements of the sequence *)

val append : 'a t -> 'a t -> 'a t
  (** Append two sequences. Iterating on the result is like iterating
      on the first, then on the second. *)

val concat : 'a t t -> 'a t
  (** Concatenate a sequence of sequences into one sequence. *)

val flatten : 'a t t -> 'a t
  (** Alias for {!concat} *)

val flatMap : ('a -> 'b t) -> 'a t -> 'b t
  (** @deprecated use {!flat_map} since NEXT_RELEASE *)

val flat_map : ('a -> 'b t) -> 'a t -> 'b t
  (** Monadic bind. Intuitively, it applies the function to every element of the
      initial sequence, and calls {!concat}.
      @since 0.5 *)

val fmap : ('a -> 'b option) -> 'a t -> 'b t
  (** @deprecated use {!filter_map} since NEXT_RELEASE *)

val filter_map : ('a -> 'b option) -> 'a t -> 'b t
  (** Map and only keep non-[None] elements
      @since 0.5 *)

val intersperse : 'a -> 'a t -> 'a t
  (** Insert the single element between every element of the sequence *)

(** {2 Caching} *)

val persistent : 'a t -> 'a t
  (** Iterate on the sequence, storing elements in an efficient internal structure..
      The resulting sequence can be iterated on as many times as needed.
      {b Note}: calling persistent on an already persistent sequence
      will still make a new copy of the sequence! *)

val persistent_lazy : 'a t -> 'a t
  (** Lazy version of {!persistent}. When calling [persistent_lazy s],
      a new sequence [s'] is immediately returned (without actually consuming
      [s]) in constant time; the first time [s'] is iterated on,
      it also consumes [s] and caches its content into a inner data
      structure that will back [s'] for future iterations.

      {b warning}: on the first traversal of [s'], if the traversal
      is interrupted prematurely ({!take}, etc.) then [s'] will not be
      memorized, and the next call to [s'] will traverse [s] again. *)

(** {2 Misc} *)

val sort : ?cmp:('a -> 'a -> int) -> 'a t -> 'a t
  (** Sort the sequence. Eager, O(n) ram and O(n ln(n)) time.
      It iterates on elements of the argument sequence immediately,
      before it sorts them. *)

val sort_uniq : ?cmp:('a -> 'a -> int) -> 'a t -> 'a t
  (** Sort the sequence and remove duplicates. Eager, same as [sort] *)

val group : ?eq:('a -> 'a -> bool) -> 'a t -> 'a list t
  (** Group equal consecutive elements.
      @deprecated use {!group_succ_by} *)

val group_succ_by : ?eq:('a -> 'a -> bool) -> 'a t -> 'a list t
  (** Group equal consecutive elements.
      Synonym to {!group}.
      @since NEXT_RELEASE *)

val group_by : ?hash:('a -> int) -> ?eq:('a -> 'a -> bool) ->
               'a t -> 'a list t
  (** Group equal elements, disregarding their order of appearance.
      The result sequence is traversable as many times as required.
      @since NEXT_RELEASE *)

val uniq : ?eq:('a -> 'a -> bool) -> 'a t -> 'a t
  (** Remove consecutive duplicate elements. Basically this is
      like [fun seq -> map List.hd (group seq)]. *)

val product : 'a t -> 'b t -> ('a * 'b) t
  (** Cartesian product of the sequences. When calling [product a b],
      the caller {b MUST} ensure that [b] can be traversed as many times
      as required (several times), possibly by calling {!persistent} on it
      beforehand. *)

val product2 : 'a t -> 'b t -> ('a, 'b) t2
  (** Binary version of {!product}. Same requirements.
      @since 0.5 *)

val join : join_row:('a -> 'b -> 'c option) -> 'a t -> 'b t -> 'c t
  (** [join ~join_row a b] combines every element of [a] with every
      element of [b] using [join_row]. If [join_row] returns None, then
      the two elements do not combine. Assume that [b] allows for multiple
      iterations. *)

val unfoldr : ('b -> ('a * 'b) option) -> 'b -> 'a t
  (** [unfoldr f b] will apply [f] to [b]. If it
      yields [Some (x,b')] then [x] is returned
      and unfoldr recurses with [b']. *)

val scan : ('b -> 'a -> 'b) -> 'b -> 'a t -> 'b t
  (** Sequence of intermediate results *)

val max : ?lt:('a -> 'a -> bool) -> 'a t -> 'a option
  (** Max element of the sequence, using the given comparison function.
      @return None if the sequence is empty, Some [m] where [m] is the maximal
      element otherwise *)

val min : ?lt:('a -> 'a -> bool) -> 'a t -> 'a option
  (** Min element of the sequence, using the given comparison function.
      see {!max} for more details. *)

val head : 'a t -> 'a option
  (** First element, if any, otherwise [None]
      @since 0.5.1 *)

val head_exn : 'a t -> 'a
  (** First element, if any, fails
      @raise Invalid_argument if the sequence is empty
      @since 0.5.1 *)

val take : int -> 'a t -> 'a t
  (** Take at most [n] elements from the sequence. Works on infinite
      sequences. *)

val take_while : ('a -> bool) -> 'a t -> 'a t
  (** Take elements while they satisfy the predicate, then stops iterating.
      Will work on an infinite sequence [s] if the predicate is false for at
      least one element of [s]. *)

val fold_while : ('a -> 'b -> 'a * [`Stop | `Continue]) -> 'a -> 'b t -> 'a
  (** Folds over elements of the sequence, stopping early if the accumulator
      returns [('a, `Stop)]
      @since 0.5.5 *)

val drop : int -> 'a t -> 'a t
  (** Drop the [n] first elements of the sequence. Lazy. *)

val drop_while : ('a -> bool) -> 'a t -> 'a t
  (** Predicate version of {!drop} *)

val rev : 'a t -> 'a t
  (** Reverse the sequence. O(n) memory and time, needs the
      sequence to be finite. The result is persistent and does
      not depend on the input being repeatable. *)

(** {2 Binary sequences} *)

val empty2 : ('a, 'b) t2

val is_empty2 : (_, _) t2 -> bool

val length2 : (_, _) t2 -> int

val zip : ('a, 'b) t2 -> ('a * 'b) t

val unzip : ('a * 'b) t -> ('a, 'b) t2

val zip_i : 'a t -> (int, 'a) t2
  (** Zip elements of the sequence with their index in the sequence *)

val fold2 : ('c -> 'a -> 'b -> 'c) -> 'c -> ('a, 'b) t2 -> 'c

val iter2 : ('a -> 'b -> unit) -> ('a, 'b) t2 -> unit

val map2 : ('a -> 'b -> 'c) -> ('a, 'b) t2 -> 'c t

val map2_2 : ('a -> 'b -> 'c) -> ('a -> 'b -> 'd) -> ('a, 'b) t2 -> ('c, 'd) t2
  (** [map2_2 f g seq2] maps each [x, y] of seq2 into [f x y, g x y] *)

(** {2 Basic data structures converters} *)

val to_list : 'a t -> 'a list
  (** Convert the sequence into a list. Preserves order of elements.
      This function is tail-recursive, but consumes 2*n memory.
      If order doesn't matter to you, consider {!to_rev_list}. *)

val to_rev_list : 'a t -> 'a list
  (** Get the list of the reversed sequence (more efficient than {!to_list}) *)

val of_list : 'a list -> 'a t

val on_list : ('a t -> 'b t) -> 'a list -> 'b list
(** [on_list f l] is equivalent to [to_list @@ f @@ of_list l].
    @since 0.5.2
*)

val to_opt : 'a t -> 'a option
  (** Alias to {!head}
      @since 0.5.1 *)

val to_array : 'a t -> 'a array
  (** Convert to an array. Currently not very efficient because
      an intermediate list is used. *)

val of_array : 'a array -> 'a t

val of_array_i : 'a array -> (int * 'a) t
  (** Elements of the array, with their index *)

val of_array2 : 'a array -> (int, 'a) t2

val array_slice : 'a array -> int -> int -> 'a t
  (** [array_slice a i j] Sequence of elements whose indexes range
      from [i] to [j] *)

val of_opt : 'a option -> 'a t
  (** Iterate on 0 or 1 values.
      @since 0.5.1 *)

val of_stream : 'a Stream.t -> 'a t
  (** Sequence of elements of a stream (usable only once) *)

val to_stream : 'a t -> 'a Stream.t
  (** Convert to a stream. linear in memory and time (a copy is made in memory) *)

val to_stack : 'a Stack.t -> 'a t -> unit
  (** Push elements of the sequence on the stack *)

val of_stack : 'a Stack.t -> 'a t
  (** Sequence of elements of the stack (same order as [Stack.iter]) *)

val to_queue : 'a Queue.t -> 'a t -> unit
  (** Push elements of the sequence into the queue *)

val of_queue : 'a Queue.t -> 'a t
  (** Sequence of elements contained in the queue, FIFO order *)

val hashtbl_add : ('a, 'b) Hashtbl.t -> ('a * 'b) t -> unit
  (** Add elements of the sequence to the hashtable, with
      Hashtbl.add *)

val hashtbl_replace : ('a, 'b) Hashtbl.t -> ('a * 'b) t -> unit
  (** Add elements of the sequence to the hashtable, with
      Hashtbl.replace (erases conflicting bindings) *)

val to_hashtbl : ('a * 'b) t -> ('a, 'b) Hashtbl.t
  (** Build a hashtable from a sequence of key/value pairs *)

val to_hashtbl2 : ('a, 'b) t2 -> ('a, 'b) Hashtbl.t
  (** Build a hashtable from a sequence of key/value pairs *)

val of_hashtbl : ('a, 'b) Hashtbl.t -> ('a * 'b) t
  (** Sequence of key/value pairs from the hashtable *)

val of_hashtbl2 : ('a, 'b) Hashtbl.t -> ('a, 'b) t2
  (** Sequence of key/value pairs from the hashtable *)

val hashtbl_keys : ('a, 'b) Hashtbl.t -> 'a t
val hashtbl_values : ('a, 'b) Hashtbl.t -> 'b t

val of_str : string -> char t
val to_str :  char t -> string

val concat_str : string t -> string
  (** Concatenate strings together, eagerly.
      Also see {!intersperse} to add a separator.
      @since 0.5 *)

exception OneShotSequence
  (** Raised when the user tries to iterate several times on
      a transient iterator *)

val of_in_channel : in_channel -> char t
  (** Iterates on characters of the input (can block when one
      iterates over the sequence). If you need to iterate
      several times on this sequence, use {!persistent}.
      @raise OneShotSequence when used more than once. *)

val to_buffer : char t -> Buffer.t -> unit
  (** Copy content of the sequence into the buffer *)

val int_range : start:int -> stop:int -> int t
  (** Iterator on integers in [start...stop] by steps 1. Also see
      {!(--)} for an infix version. *)

val int_range_dec : start:int -> stop:int -> int t
  (** Iterator on decreasing integers in [stop...start] by steps -1.
      See {!(--^)} for an infix version *)

val bools : bool t
  (** Iterates on [true] and [false]
      @since NEXT_RELEASE *)

val of_set : (module Set.S with type elt = 'a and type t = 'b) -> 'b -> 'a t
  (** Convert the given set to a sequence. The set module must be provided. *)

val to_set : (module Set.S with type elt = 'a and type t = 'b) -> 'a t -> 'b
  (** Convert the sequence to a set, given the proper set module *)

type 'a gen = unit -> 'a option
type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]

val of_gen : 'a gen -> 'a t
  (** Traverse eagerly the generator and build a sequence from it *)

val to_gen : 'a t -> 'a gen
  (** Make the sequence persistent (O(n)) and then iterate on it. Eager. *)

val of_klist : 'a klist -> 'a t
  (** Iterate on the lazy list *)

val to_klist : 'a t -> 'a klist
  (** Make the sequence persistent and then iterate on it. Eager. *)

(** {2 Functorial conversions between sets and sequences} *)

module Set : sig
  module type S = sig
    include Set.S
    val of_seq : elt sequence -> t
    val to_seq : t -> elt sequence
    val to_list : t -> elt list
    val of_list : elt list -> t
  end

  (** Create an enriched Set module from the given one *)
  module Adapt(X : Set.S) : S with type elt = X.elt and type t = X.t

  (** Functor to build an extended Set module from an ordered type *)
  module Make(X : Set.OrderedType) : S with type elt = X.t
end

(** {2 Conversion between maps and sequences.} *)

module Map : sig
  module type S = sig
    include Map.S
    val to_seq : 'a t -> (key * 'a) sequence
    val of_seq : (key * 'a) sequence -> 'a t
    val keys : 'a t -> key sequence
    val values : 'a t -> 'a sequence
    val to_list : 'a t -> (key * 'a) list
    val of_list : (key * 'a) list -> 'a t
  end

  (** Adapt a pre-existing Map module to make it sequence-aware *)
  module Adapt(M : Map.S) : S with type key = M.key and type 'a t = 'a M.t

  (** Create an enriched Map module, with sequence-aware functions *)
  module Make(V : Map.OrderedType) : S with type key = V.t
end

(** {2 Infinite sequences of random values} *)

val random_int : int -> int t
  (** Infinite sequence of random integers between 0 and
      the given higher bound (see Random.int) *)

val random_bool : bool t
  (** Infinite sequence of random bool values *)

val random_float : float -> float t

val random_array : 'a array -> 'a t
  (** Sequence of choices of an element in the array *)

val random_list : 'a list -> 'a t
  (** Infinite sequence of random elements of the list. Basically the
      same as {!random_array}. *)

(** {2 Infix functions} *)

module Infix : sig
  val (--) : int -> int -> int t
    (** [a -- b] is the range of integers from [a] to [b], both included,
        in increasing order. It will therefore be empty if [a > b]. *)

  val (--^) : int -> int -> int t
    (** [a --^ b] is the range of integers from [b] to [a], both included,
        in decreasing order (starts from [a]).
        It will therefore be empty if [a < b]. *)

  val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
    (** Monadic bind (infix version of {!flat_map}
        @since 0.5 *)

  val (>|=) : 'a t -> ('a -> 'b) -> 'b t
    (** Infix version of {!map}
        @since 0.5 *)

  val (<*>) : ('a -> 'b) t -> 'a t -> 'b t
    (** Applicative operator (product+application)
        @since 0.5 *)

  val (<+>) : 'a t -> 'a t -> 'a t
    (** Concatenation of sequences
        @since 0.5 *)
end

include module type of Infix

(** {2 Pretty printing of sequences} *)

val pp_seq : ?sep:string -> (Format.formatter -> 'a -> unit) ->
             Format.formatter -> 'a t -> unit
  (** Pretty print a sequence of ['a], using the given pretty printer
      to print each elements. An optional separator string can be provided. *)

val pp_buf : ?sep:string -> (Buffer.t -> 'a -> unit) ->
             Buffer.t -> 'a t -> unit
  (** Print into a buffer *)

val to_string : ?sep:string -> ('a -> string) -> 'a t -> string
  (** Print into a string *)

(** {2 Basic IO}

Very basic interface to manipulate files as sequence of chunks/lines. The
sequences take care of opening and closing files properly; every time
one iterates over a sequence, the file is opened/closed again.

Example: copy a file ["a"] into file ["b"], removing blank lines:

{[
  Sequence.(IO.lines_of "a" |> filter (fun l-> l<> "") |> IO.write_lines "b");;
]}

By chunks of [4096] bytes:

{[
  Sequence.IO.(chunks_of ~size:4096 "a" |> write_to "b");;
]}

Read the lines of a file into a list:

{[
  Sequence.IO.lines "a" |> Sequence.to_list
]}

@since 0.5.1 *)

module IO : sig
  val lines_of : ?mode:int -> ?flags:open_flag list ->
                string -> string t
  (** [lines_of filename] reads all lines of the given file. It raises the
      same exception as would opening the file and read from it, except
      from [End_of_file] (which is caught). The file is {b always} properly
      closed.
      Every time the sequence is iterated on, the file is opened again, so
      different iterations might return different results
      @param mode default [0o644]
      @param flags default: [[Open_rdonly]] *)

  val chunks_of : ?mode:int -> ?flags:open_flag list -> ?size:int ->
                  string -> string t
  (** Read chunks of the given [size] from the file. The last chunk might be
      smaller. Behaves like {!lines_of} regarding errors and options.
      Every time the sequence is iterated on, the file is opened again, so
      different iterations might return different results *)

  val write_to : ?mode:int -> ?flags:open_flag list ->
                     string -> string t -> unit
  (** [write_to filename seq] writes all strings from [seq] into the given
      file. It takes care of opening and closing the file.
      @param mode default [0o644]
      @param flags used by [open_out_gen]. Default: [[Open_creat;Open_wronly]]. *)

  val write_bytes_to : ?mode:int -> ?flags:open_flag list ->
                       string -> Bytes.t t -> unit
  (** @since 0.5.4 *)

  val write_lines : ?mode:int -> ?flags:open_flag list ->
                        string -> string t -> unit
  (** Same as {!write_to}, but intercales ['\n'] between each string *)

  val write_bytes_lines : ?mode:int -> ?flags:open_flag list ->
                    string -> Bytes.t t -> unit
  (** @since 0.5.4 *)
end