package containers

  1. Overview
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Values of type 'a Gen.t represent a possibly infinite sequence of values of type 'a. One can only iterate once on the sequence, as it is consumed by iteration/deconstruction/access. None is returned when the generator is exhausted. Most functions consume elements.

The submodule Restart provides utilities to work with restartable generators, that is, functions unit -> 'a Gen.t that allow to build as many generators from the same source as needed.

Global type declarations

type 'a t = unit -> 'a option

A generator may be called several times, yielding the next value each time. It returns None when no elements remain

type 'a gen = 'a t
module type S = Gen_intf.S

NOTE: version informations ("@since" annotations) in CCGen_intf will not be reliable, for they will represent versions of Gen rather than containers.

Transient generators

val get : 'a t -> 'a option

Get the next value

val next : 'a t -> 'a option

Synonym for get

val get_exn : 'a t -> 'a

Get the next value, or fails

  • raises Invalid_argument

    if no element remains

val junk : 'a t -> unit

Drop the next value, discarding it.

val repeatedly : (unit -> 'a) -> 'a t

Call the same function an infinite number of times (useful for instance if the function is a random generator).

Operations on transient generators

include S with type 'a t := 'a gen
val empty : 'a gen

Empty generator, with no elements

val singleton : 'a -> 'a gen

One-element generator

val repeat : 'a -> 'a gen

Repeat same element endlessly

val iterate : 'a -> ('a -> 'a) -> 'a gen

iterate x f is [x; f x; f (f x); f (f (f x)); ...]

val unfold : ('b -> ('a * 'b) option) -> 'b -> 'a gen

Dual of fold, with a deconstructing operation. It keeps on unfolding the 'b value into a new 'b, and a 'a which is yielded, until None is returned.

val init : ?limit:int -> (int -> 'a) -> 'a gen

Calls the function, starting from 0, on increasing indices. If limit is provided and is a positive int, iteration will stop at the limit (excluded). For instance init ~limit:4 id will yield 0, 1, 2, and 3.

Basic combinators

val is_empty : _ gen -> bool

Check whether the enum is empty. Pops an element, if any

val fold : ('b -> 'a -> 'b) -> 'b -> 'a gen -> 'b

Fold on the generator, tail-recursively. Consumes the generator.

val reduce : ('a -> 'a -> 'a) -> 'a gen -> 'a

Fold on non-empty sequences. Consumes the generator.

  • raises Invalid_argument

    on an empty gen

val scan : ('b -> 'a -> 'b) -> 'b -> 'a gen -> 'b gen

Like fold, but keeping successive values of the accumulator. Consumes the generator.

val unfold_scan : ('b -> 'a -> 'b * 'c) -> 'b -> 'a gen -> 'c gen

A mix of unfold and scan. The current state is combined with the current element to produce a new state, and an output value of type 'c.

  • since 0.2.2
val iter : ('a -> unit) -> 'a gen -> unit

Iterate on the enum, consumes it.

val iteri : (int -> 'a -> unit) -> 'a gen -> unit

Iterate on elements with their index in the enum, from 0, consuming it.

val length : _ gen -> int

Length of an enum (linear time), consuming it

val map : ('a -> 'b) -> 'a gen -> 'b gen

Lazy map. No iteration is performed now, the function will be called when the result is traversed.

val append : 'a gen -> 'a gen -> 'a gen

Append the two enums; the result contains the elements of the first, then the elements of the second enum.

val flatten : 'a Gen_intf.gen gen -> 'a gen

Flatten the enumeration of generators

val flat_map : ('a -> 'b Gen_intf.gen) -> 'a gen -> 'b gen

Monadic bind; each element is transformed to a sub-enum which is then iterated on, before the next element is processed, and so on.

val mem : ?eq:('a -> 'a -> bool) -> 'a -> 'a gen -> bool

Is the given element, member of the enum?

val take : int -> 'a gen -> 'a gen

Take at most n elements

val drop : int -> 'a gen -> 'a gen

Drop n elements

val nth : int -> 'a gen -> 'a

n-th element, or Not_found

  • raises Not_found

    if the generator contains less than n arguments

val take_nth : int -> 'a gen -> 'a gen

take_nth n g returns every element of g whose index is a multiple of n. For instance take_nth 2 (1--10) |> to_list will return 1;3;5;7;9

val filter : ('a -> bool) -> 'a gen -> 'a gen

Filter out elements that do not satisfy the predicate.

val take_while : ('a -> bool) -> 'a gen -> 'a gen

Take elements while they satisfy the predicate

val drop_while : ('a -> bool) -> 'a gen -> 'a gen

Drop elements while they satisfy the predicate

val filter_map : ('a -> 'b option) -> 'a gen -> 'b gen

Maps some elements to 'b, drop the other ones

val zip_index : 'a gen -> (int * 'a) gen

Zip elements with their index in the enum

val unzip : ('a * 'b) gen -> 'a gen * 'b gen

Unzip into two sequences, splitting each pair

val partition : ('a -> bool) -> 'a gen -> 'a gen * 'a gen

partition p l returns the elements that satisfy p, and the elements that do not satisfy p

val for_all : ('a -> bool) -> 'a gen -> bool

Is the predicate true for all elements?

val exists : ('a -> bool) -> 'a gen -> bool

Is the predicate true for at least one element?

val min : ?lt:('a -> 'a -> bool) -> 'a gen -> 'a

Minimum element, according to the given comparison function.

  • raises Invalid_argument

    if the generator is empty

val max : ?lt:('a -> 'a -> bool) -> 'a gen -> 'a

Maximum element, see min

  • raises Invalid_argument

    if the generator is empty

val eq : ?eq:('a -> 'a -> bool) -> 'a gen -> 'a gen -> bool

Equality of generators.

val lexico : ?cmp:('a -> 'a -> int) -> 'a gen -> 'a gen -> int

Lexicographic comparison of generators. If a generator is a prefix of the other one, it is considered smaller.

val compare : ?cmp:('a -> 'a -> int) -> 'a gen -> 'a gen -> int

Synonym for lexico

val find : ('a -> bool) -> 'a gen -> 'a option

find p e returns the first element of e to satisfy p, or None.

val sum : int gen -> int

Sum of all elements

Multiple iterators

val map2 : ('a -> 'b -> 'c) -> 'a gen -> 'b gen -> 'c gen

Map on the two sequences. Stops once one of them is exhausted.

val iter2 : ('a -> 'b -> unit) -> 'a gen -> 'b gen -> unit

Iterate on the two sequences. Stops once one of them is exhausted.

val fold2 : ('acc -> 'a -> 'b -> 'acc) -> 'acc -> 'a gen -> 'b gen -> 'acc

Fold the common prefix of the two iterators

val for_all2 : ('a -> 'b -> bool) -> 'a gen -> 'b gen -> bool

Succeeds if all pairs of elements satisfy the predicate. Ignores elements of an iterator if the other runs dry.

val exists2 : ('a -> 'b -> bool) -> 'a gen -> 'b gen -> bool

Succeeds if some pair of elements satisfy the predicate. Ignores elements of an iterator if the other runs dry.

val zip_with : ('a -> 'b -> 'c) -> 'a gen -> 'b gen -> 'c gen

Combine common part of the enums (stops when one is exhausted)

val zip : 'a gen -> 'b gen -> ('a * 'b) gen

Zip together the common part of the enums

Complex combinators

val merge : 'a Gen_intf.gen gen -> 'a gen

Pick elements fairly in each sub-generator. The merge of enums e1, e2, ... picks elements in e1, e2, in e3, e1, e2 .... Once a generator is empty, it is skipped; when they are all empty, and none remains in the input, their merge is also empty. For instance, merge [1;3;5] [2;4;6] will be, in disorder, 1;2;3;4;5;6.

val intersection : ?cmp:('a -> 'a -> int) -> 'a gen -> 'a gen -> 'a gen

Intersection of two sorted sequences. Only elements that occur in both inputs appear in the output

val sorted_merge : ?cmp:('a -> 'a -> int) -> 'a gen -> 'a gen -> 'a gen

Merge two sorted sequences into a sorted sequence

val sorted_merge_n : ?cmp:('a -> 'a -> int) -> 'a gen list -> 'a gen

Sorted merge of multiple sorted sequences

val tee : ?n:int -> 'a gen -> 'a Gen_intf.gen list

Duplicate the enum into n generators (default 2). The generators share the same underlying instance of the enum, so the optimal case is when they are consumed evenly

val round_robin : ?n:int -> 'a gen -> 'a Gen_intf.gen list

Split the enum into n generators in a fair way. Elements with index = k mod n with go to the k-th enum. n default value is 2.

val interleave : 'a gen -> 'a gen -> 'a gen

interleave a b yields an element of a, then an element of b, and so on. When a generator is exhausted, this behaves like the other generator.

val intersperse : 'a -> 'a gen -> 'a gen

Put the separator element between all elements of the given enum

val product : 'a gen -> 'b gen -> ('a * 'b) gen

Cartesian product, in no predictable order. Works even if some of the arguments are infinite.

val group : ?eq:('a -> 'a -> bool) -> 'a gen -> 'a list gen

Group equal consecutive elements together.

val uniq : ?eq:('a -> 'a -> bool) -> 'a gen -> 'a gen

Remove consecutive duplicate elements. Basically this is like fun e -> map List.hd (group e).

val sort : ?cmp:('a -> 'a -> int) -> 'a gen -> 'a gen

Sort according to the given comparison function. The enum must be finite.

val sort_uniq : ?cmp:('a -> 'a -> int) -> 'a gen -> 'a gen

Sort and remove duplicates. The enum must be finite.

val chunks : int -> 'a gen -> 'a array gen

chunks n e returns a generator of arrays of length n, composed of successive elements of e. The last array may be smaller than n

val permutations : 'a gen -> 'a list gen

Permutations of the enum.

  • since 0.2.2
val combinations : int -> 'a gen -> 'a list gen

Combinations of given length. The ordering of the elements within each combination is unspecified. Example (ignoring ordering): combinations 2 (1--3) |> to_list = [[1;2]; [1;3]; [2;3]]

  • since 0.2.2
val power_set : 'a gen -> 'a list gen

All subsets of the enum (in no particular order). The ordering of the elements within each subset is unspecified.

  • since 0.2.2

Basic conversion functions

val of_list : 'a list -> 'a gen

Enumerate elements of the list

val to_list : 'a gen -> 'a list

non tail-call trasnformation to list, in the same order

val to_rev_list : 'a gen -> 'a list

Tail call conversion to list, in reverse order (more efficient)

val to_array : 'a gen -> 'a array

Convert the enum to an array (not very efficient)

val of_array : ?start:int -> ?len:int -> 'a array -> 'a gen

Iterate on (a slice of) the given array

val rand_int : int -> int gen

Random ints in the given range.

val int_range : int -> int -> int gen

int_range a b enumerates integers between a and b, included. a is assumed to be smaller than b.

module Infix : sig ... end
val (--) : int -> int -> int gen

Synonym for int_range

val (>>=) : 'a gen -> ('a -> 'b Gen_intf.gen) -> 'b gen

Monadic bind operator

val pp : ?start:string -> ?stop:string -> ?sep:string -> ?horizontal:bool -> (Format.formatter -> 'a -> unit) -> Format.formatter -> 'a gen -> unit

Pretty print the content of the generator on a formatter.

Restartable generators

module Restart : sig ... end


val persistent : 'a t -> 'a Restart.t

Store content of the transient generator in memory, to be able to iterate on it several times later. If possible, consider using combinators from Restart directly instead.

val persistent_lazy : 'a t -> 'a Restart.t

Same as persistent, but consumes the generator on demand (by chunks). This allows to make a restartable generator out of an ephemeral one, without paying a big cost upfront (nor even consuming it fully).

  • since 0.6.1
val start : 'a Restart.t -> 'a t

Create a new transient generator. start gen is the same as gen () but is included for readability.


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