#### containers

Library

Module

Module type

Parameter

Class

Class type

## Generators

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

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 get_exn : 'a t -> 'a`

Get the next value, or fails

`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.

Like `fold`

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

`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

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

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

n-th element, or Not_found

`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`

Filter out elements that do not satisfy the predicate.

Maps some elements to 'b, drop the other ones

`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.

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

`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

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

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

Fold the common prefix of the two iterators

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

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

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

### 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`

.

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

Merge two sorted sequences into a sorted sequence

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.

`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.

Put the separator element between all elements of the given enum

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

Group equal consecutive elements together.

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

.

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

Sort and remove duplicates. The enum must be finite.

`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`

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]]`

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

### 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 (>>=) : '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`

### Utils

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.

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).