module BatStream:`sig`

..`end`

Streams and stream parsers

Streams are a read-and-forget data structure, comparable to enumerations.
In Batteries Included, streams are deprecated in favor of enumerations,
defined in module `BatEnum`

.

**Note** This module is provided essentially for backwards-compatibility.
If you feel like using `Stream.t`

, please take a look at `BatEnum`

or `LazyList`

.

This module is based on Zheng Li's SDFlow

This module replaces Stdlib's Stream module.

**Author(s):**Zheng Li (SDFlow), David Teller

type`'a`

t =`'a Stdlib.Stream.t`

`include BatEnum.Enumerable`

`include BatInterfaces.Mappable`

The type of streams holding values of type `'a`

.

`exception Failure`

Raised by parsers when none of the first components of the stream patterns is accepted.

`exception Error of ``string`

Raised by parsers when the first component of a stream pattern is accepted, but one of the following components is rejected.

`val from : ``(int -> 'a option) -> 'a t`

`Stream.from f`

returns a stream built from the function `f`

.
To create a new stream element, the function `f`

is called with
the current stream count. The user function `f`

must return either
`Some <value>`

for a value or `None`

to specify the end of the
stream.

`val of_list : ``'a list -> 'a t`

Return the stream holding the elements of the list in the same order.

`val of_string : ``string -> char t`

Return the stream of the characters of the string parameter.

`val of_bytes : ``Stdlib.Bytes.t -> char t`

Return the stream of the characters of the bytes parameter.

**Since**2.3.0

`val of_channel : ``Stdlib.in_channel -> char t`

Return the stream of the characters read from the input channel.

Warning: these functions create streams with fast access; it is illegal
to mix them with streams built with `[< >]`

; would raise `Failure`

when accessing such mixed streams.

`val of_fun : ``(unit -> 'a) -> 'a t`

`Stream.of_fun f`

returns a stream built from the function `f`

.
To create a new stream element, the function `f`

is called with
the current stream count. The user function `f`

must return either
`Some <value>`

for a value or `None`

to specify the end of the
stream.

`val iter : ``('a -> unit) -> 'a t -> unit`

`Stream.iter f s`

scans the whole stream s, applying function `f`

in turn to each stream element encountered.

`val foldl : ``('a -> 'b -> 'a * bool option) -> 'a -> 'b t -> 'a`

`foldl f init stream`

is a lazy fold_left. `f accu elt`

should return
`(new_accu, state)`

where `new_accu`

is normal accumulation result, and
`state`

is a flag representing whether the computation should continue
and whether the last operation is valid: `None`

means continue, `Some b`

means stop where `b = true`

means the last addition is still valid and `b`

means the last addition is invalid and should be revert.

= false

`val foldr : ``('a -> 'b lazy_t -> 'b) -> 'b -> 'a t -> 'b`

`foldr f init stream`

is a lazy fold_right. Unlike the normal fold_right,
the accumulation parameter of `f elt accu`

is lazy, hence it can decide
not to force the evaluation of `accu`

if the current element `elt`

can
determine the result by itself.

`val fold : ``('a -> 'a -> 'a * bool option) -> 'a t -> 'a`

`fold`

is `foldl`

without initialization value, where the first
element of stream is taken as `init`

. It raises `End_of_stream`

exception
when the input stream is empty.

`val filter : ``('a -> bool) -> 'a t -> 'a t`

`filter test stream`

picks all the elements satisfying `test`

from `stream`

and return the results in the same order as a stream.

`val next : ``'a t -> 'a`

Return the first element of the stream and remove it from the stream.

**Raises**`Stream.Failure`

if the stream is empty.

`val empty : ``'a t -> unit`

Return `()`

if the stream is empty, else raise `Stream.Failure`

.

`val peek : ``'a t -> 'a option`

Return `Some`

of "the first element" of the stream, or `None`

if
the stream is empty.

`val junk : ``'a t -> unit`

Remove the first element of the stream, possibly unfreezing it before.

`val count : ``'a t -> int`

Return the current count of the stream elements, i.e. the number of the stream elements discarded.

`val npeek : ``int -> 'a t -> 'a list`

`npeek n`

returns the list of the `n`

first elements of
the stream, or all its remaining elements if less than `n`

elements are available.

`val enum : ``'a t -> 'a BatEnum.t`

Convert a stream to an enumeration. Reading the resulting enumeration will consume elements from the stream. This is the preferred manner of converting from a stream to any other data structure.

`val of_enum : ``'a BatEnum.t -> 'a t`

Convert an enumeration to a stream. Reading the resulting stream will consume elements from the enumeration. This is the preferred manner of creating a stream.

`val of_input : ``BatIO.input -> char t`

Convert an `input`

to a stream.

`val to_list : ``'a t -> 'a list`

Convert a stream to a list

`val to_string : ``char t -> string`

convert stream of chars to string, using buffer

`val to_string_fmt : ``('a -> string, unit, string) Stdlib.format -> 'a t -> string`

convert stream to string, using Printf with given format

`val to_string_fun : ``('a -> string) -> 'a t -> string`

convert stream to string, using given conversion function

`val on_output : ``'a BatIO.output -> char t -> unit`

Convert an `output`

to a stream.

All the functions in this part are lazy.

`val map : ``('a -> 'b) -> 'a t -> 'b t`

`map f stream`

applies `f`

in turn to elements from `stream`

and return the
results as a stream in the same order.

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

`map2 f streama streamb`

applies `f`

in turn to elements of corresponding
positions from `streama`

and `streamb`

. The results are constructed in the
same order as a stream. If one stream is short, excess elements of the longer
stream are ignored.

`val scanl : ``('a -> 'b -> 'a) -> 'a -> 'b t -> 'a t`

`scanl f init stream`

returns a stream of successive reduced
values from the left: `scanl f init [< 'e0; 'e1; ... >]`

is
equivalent to
`[< 'init; '(f init e0); '(f (f init e0) e1); ... >]`

`val scan : ``('a -> 'a -> 'a) -> 'a t -> 'a t`

`scan`

is similar to `scanl`

but without the `init`

value:
`scanl f init [< 'e0; 'e1; 'e2; ... >]`

is equivalent to
`[< 'e0; '(f e0 e1); '(f (f e0 e1) e2); ... >]`

`val concat : ``'a t t -> 'a t`

concatenate a stream of streams

`val concat_map : ``('a -> 'b t) -> 'a t -> 'b t`

Composition of `BatStream.concat`

and `BatStream.map`

.
`concat_map f e`

is the same as `concat (map f e)`

.

**Since**2.3.0

`val take : ``int -> 'a t -> 'a t`

`take n stream`

returns the prefix of `stream`

of length `n`

, or `stream`

itself if `n`

is greater than the length of `stream`

`val drop : ``int -> 'a t -> 'a t`

`drop n stream`

returns the suffix of `stream`

after the first `n`

elements,
or a empty stream if `n`

is greater than the length of `stream`

`val take_while : ``('a -> bool) -> 'a t -> 'a t`

`take_while test stream`

returns the longest (possibly empty) prefix of
`stream`

of elements that satisfy `test`

.

`val drop_while : ``('a -> bool) -> 'a t -> 'a t`

`drop_while test stream`

returns the remaining suffix of `take_while test`

.

stream

All the functions in this part are lazy.

`val dup : ``'a t -> 'a t * 'a t`

`dup stream`

returns a pair of streams which are identical to `stream`

. Note
that stream is a destructive data structure, the point of `dup`

is to
return two streams can be used independently.

NOT IMPLEMENTED CORRECTLY - WILL RAISE Failure UNTIL CORRECT IMPLEMENTATION FOUND

`val comb : ``'a t * 'b t -> ('a * 'b) t`

`comb`

transform a pair of stream into a stream of pairs of corresponding
elements. If one stream is short, excess elements of the longer stream are
ignored.

`val split : ``('a * 'b) t -> 'a t * 'b t`

`split`

is the opposite of `comb`

`val merge : ``(bool -> 'a -> bool) -> 'a t * 'a t -> 'a t`

`merge test (streama, streamb)`

merge the elements from `streama`

and
`streamb`

into a single stream. The `bool`

type here represents the id of the
two input streams where `true`

is the first and `false`

represents the
second. The `test`

function is applied to each element of the output stream
together with the id of the input stream from which it was extracted, to
decide which stream should the next element come from. The first element is
always taken from `streama`

. When a stream runs out of elements, the merge
process will continue to take elements from the other stream until both
streams reach their ends.

`val switch : ``('a -> bool) -> 'a t -> 'a t * 'a t`

`switch test stream`

split `stream`

into two streams, where the first stream have
all the elements satisfying `test`

, the second stream is opposite. The
order of elements in the source stream is preserved.

All the functions in this part are lazy.

`val cons : ``'a -> 'a t -> 'a t`

`cons x stream`

equals `[<'x; stream>]`

.

`val apnd : ``'a t -> 'a t -> 'a t`

`apnd fla flb`

equals `[<fla;flb>]`

.

`val is_empty : ``'a t -> bool`

`is_empty stream`

tests whether `stream`

is empty. But note that it forces
the evaluation of the head element if any.

`val next : ``'a t -> 'a`

Return the first element of the stream and remove it from the stream.

**Raises**`Stream.Failure`

if the stream is empty.

module StreamLabels:`sig`

..`end`