#### gen

Library

Module

Module type

Parameter

Class

Class type

## Generators

Label version of `Gen`

### 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 = GenLabels_intf.S`

### 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

**Note**: those combinators, applied to generators (not restartable generators) *consume* their argument. Sometimes they consume it lazily, sometimes eagerly, but in any case once `f gen`

has been called (with `f`

a combinator), `gen`

shouldn't be used anymore.

`val is_empty : _ gen -> bool`

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

`val fold : f:( 'b -> 'a -> 'b ) -> init:'b -> 'a gen -> 'b`

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

`val reduce : f:( '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 : f:( 'a -> unit ) -> 'a gen -> unit`

Iterate on the gen, consumes it.

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

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

`val length : _ gen -> int`

Length of an gen (linear time), consuming it

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

Lazy map with indexing starting from 0. No iteration is performed now, the function will be called when the result is traversed.

Lazy fold and map. No iteration is performed now, the function will be called when the result is traversed. The result is an iterator over the successive states of the fold.

Append the two gens; the result contains the elements of the first, then the elements of the second gen.

`val flatten : 'a GenLabels_intf.gen gen -> 'a gen`

Flatten the generator of generators

`val flat_map : f:( 'a -> 'b GenLabels_intf.gen ) -> 'a gen -> 'b gen`

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

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

Is the given element, member of the gen?

`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.

Take elements while they satisfy the predicate. The initial generator itself is not to be used anymore after this.

```
val fold_while :
f:( 'a -> 'b -> 'a * [ `Stop | `Continue ] ) ->
init:'a ->
'b gen ->
'a
```

Fold elements until (`'a, `Stop`

) is indicated by the accumulator.

Drop elements while they satisfy the predicate. The initial generator itself should not be used anymore, only the result of `drop_while`

.

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 : f:( 'a -> bool ) -> 'a gen -> bool`

Is the predicate true for all elements?

`val exists : f:( '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 : f:( '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 gens (stops when one is exhausted)

### Complex combinators

`val merge : 'a GenLabels_intf.gen gen -> 'a gen`

Pick elements fairly in each sub-generator. The merge of gens `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 GenLabels_intf.gen list`

Duplicate the gen into `n`

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

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

Split the gen into `n`

generators in a fair way. Elements with `index = k mod n`

with go to the k-th gen. `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 gen

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 gen must be finite.

Sort and remove duplicates. The gen 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 gen (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 gen 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 of_string : ?start:int -> ?len:int -> string -> char gen`

Iterate on bytes of the string

`val to_string : char gen -> string`

Convert into a string

`val rand_int : int -> int gen`

Random ints in the given range.

`val int_range : ?step:int -> int -> int -> int gen`

`int_range ~step a b`

generates integers between `a`

and `b`

, included, with steps of length `step`

(1 if omitted). `a`

is assumed to be smaller than `b`

. `step`

must not be null, but it can be negative for decreasing integers.

`module Infix : sig ... end`

`val (--) : int -> int -> int gen`

Synonym for ` int_range ~by:1`

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

`val to_iter : 'a gen -> 'a GenLabels_intf.iter`

### 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). Optional parameters: see `GenMList.of_gen_lazy`

.

`peek g`

transforms the generator `g`

into a generator of `x, Some next`

if `x`

was followed by `next`

in `g`

, or `x, None`

if `x`

was the last element of `g`

`peek_n ~n g`

iterates on `g`

, returning along with each element the array of the (at most) `n`

elements that follow it immediately

Create a new transient generator. `start gen`

is the same as `gen ()`

but is included for readability.

### Basic IO

Very basic interface to manipulate files as sequence of chunks/lines.

`module IO : sig ... end`