Module BatStream

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 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.

Stream builders

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 : Bytes.t -> char t
Return the stream of the characters of the bytes parameter.
Since 2.3.0
val of_channel : Pervasives.in_channel -> char t
Return the stream of the characters read from the input channel.

Other Stream builders

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.

Stream iterator

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
    = false
means the last addition is invalid and should be revert.
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 determin 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.

Predefined parsers

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.

Useful functions

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.

Conversion functions

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) Pervasives.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

Stream consumers

val on_output : 'a BatIO.output -> char t -> unit
Convert an output to a stream.

Computation over 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
.

Streams pair arithmetic

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.

Stream arithmetic

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.

Predefined parsers

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