1Seq(3)                           OCaml library                          Seq(3)
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NAME

6       Seq -  Functional Iterators
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Module

9       Module   Seq
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Documentation

12       Module Seq
13        : sig end
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17   Functional Iterators
18       The  type  'a t is a delayed list, i.e. a list where some evaluation is
19       needed to access the next element. This makes it possible to build  in‐
20       finite sequences, to build sequences as we traverse them, and to trans‐
21       form them in a lazy fashion rather than upfront.
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23       type 'a t = unit -> 'a node
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26       The type of delayed lists containing elements of type 'a .   Note  that
27       the  concrete  list node 'a node is delayed under a closure, not a lazy
28       block, which means it might be recomputed every time we access it.
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31       type 'a node =
32        | Nil
33        | Cons of 'a * 'a t
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36       A fully-evaluated list node, either empty or containing an element  and
37       a delayed tail.
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41       val empty : 'a t
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43       The empty sequence, containing no elements.
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47       val return : 'a -> 'a t
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49       The singleton sequence containing only the given element.
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53       val cons : 'a -> 'a t -> 'a t
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56       cons  x xs is the sequence containing the element x followed by the se‐
57       quence xs
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61       Since 4.11
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65       val append : 'a t -> 'a t -> 'a t
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68       append xs ys is the sequence xs followed by the sequence ys
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72       Since 4.11
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76       val map : ('a -> 'b) -> 'a t -> 'b t
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79       map f seq returns a new sequence whose elements are the elements of seq
80       , transformed by f .  This transformation is lazy, it only applies when
81       the result is traversed.
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83       If seq = [1;2;3] , then map f seq = [f 1; f 2; f 3] .
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87       val filter : ('a -> bool) -> 'a t -> 'a t
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89       Remove from the sequence the elements that do  not  satisfy  the  given
90       predicate.   This  transformation is lazy, it only applies when the re‐
91       sult is traversed.
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95       val filter_map : ('a -> 'b option) -> 'a t -> 'b t
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97       Apply the function to every element; if f x = None then x  is  dropped;
98       if  f  x  = Some y then y is returned.  This transformation is lazy, it
99       only applies when the result is traversed.
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103       val flat_map : ('a -> 'b t) -> 'a t -> 'b t
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105       Map each element to a subsequence, then return  each  element  of  this
106       sub-sequence  in  turn.   This  transformation is lazy, it only applies
107       when the result is traversed.
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111       val fold_left : ('a -> 'b -> 'a) -> 'a -> 'b t -> 'a
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113       Traverse the sequence from left to right, combining each  element  with
114       the  accumulator using the given function.  The traversal happens imme‐
115       diately and will not terminate on infinite sequences.
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117       Also see List.fold_left
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122       val iter : ('a -> unit) -> 'a t -> unit
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124       Iterate on the sequence, calling the (imperative) function on every el‐
125       ement.  The traversal happens immediately and will not terminate on in‐
126       finite sequences.
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130       val unfold : ('b -> ('a * 'b) option) -> 'b -> 'a t
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132       Build a sequence from a step function and an initial value.  unfold f u
133       returns  empty  if f u returns None , or fun () -> Cons (x, unfold f y)
134       if f u returns Some (x, y) .
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136       For example, unfold (function [] -> None | h::t ->  Some  (h,t))  l  is
137       equivalent to List.to_seq l .
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140       Since 4.11
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146OCamldoc                          2021-01-26                            Seq(3)