# Module BatPervasives

    module BatPervasives: sig .. end

###### Additional functions.

Author(s): Xavier Leroy (Base module), Nicolas Cannasse, David Teller, Zheng Li

The initially opened module.

This module provides the basic operations over the built-in types (numbers, booleans, strings, exceptions, references, lists, arrays, input-output channels, ...)

This module is automatically opened at the beginning of each compilation. All components of this module can therefore be referred by their short name, without prefixing them by `BatPervasives`.

###### String operations

More string operations are provided in module `BatString`.

    val uppercase : string -> string

Return a copy of the argument, with all lowercase letters translated to uppercase, including accented letters of the ISO Latin-1 (8859-1) character set.

    val lowercase : string -> string

Return a copy of the argument, with all uppercase letters translated to lowercase, including accented letters of the ISO Latin-1 (8859-1) character set.

###### String conversion functions

These are the most common string conversion functions. For additional string conversion functions, see in the corresponding module (e.g. for conversion between `int32` and `string`, see module `Int32`).

    val string_of_char : char -> string

creates a string from a char.

    val dump : 'a -> string

Attempt to convert a value to a string.

Since types are lost at compile time, the representation might not match your type. For example, None will be printed 0 since they share the same runtime representation.

###### List operations

More list operations are provided in module `List`.

    val (@) : 'a list -> 'a list -> 'a list

List concatenation.

###### Input/output

This section only contains the most common input/output operations. More operations may be found in modules `BatIO` and `File`.

    val stdin : BatIO.input

Standard input, as per Unix/Windows conventions (by default, keyboard).

Use this input to read what the user is writing on the keyboard.

    val stdout : unit BatIO.output

Standard output, as per Unix/Windows conventions (by default, console).

Use this output to display regular messages.

    val stderr : unit BatIO.output

Standard error output, as per Unix/Windows conventions.

Use this output to display warnings and error messages.

    val stdnull : unit BatIO.output

An output which discards everything written to it.

Use this output to ignore messages.

    val flush_all : unit -> unit

Write all pending data to output channels, ignore all errors.

It is normally not necessary to call this function, as all pending data is written when an output channel is closed or when the program itself terminates, either normally or because of an uncaught exception. However, this function is useful for debugging, as it forces pending data to be written immediately.

Output functions on standard output

    val print_bool : bool -> unit

Print a boolean on standard output.

    val print_guess : 'a BatIO.output -> 'b -> unit

Attempt to print the representation of a runtime value on the standard output. See remarks for `BatPervasives.dump`. This function is useful mostly for debugging. As a general rule, it should not be used in production code.

    val print_all : BatIO.input -> unit

Print the contents of an input to the standard output.
Output functions on standard error

    val prerr_bool : bool -> unit

Print a boolean to stderr.

    val prerr_guess : 'a -> unit

Attempt to print the representation of a runtime value on the error output. See remarks for `BatPervasives.dump`. This function is useful mostly for debugging.

    val prerr_all : BatIO.input -> unit

Print the contents of an input to the error output.
General output functions

    val open_out : ?mode:BatFile.open_out_flag list ->
           ?perm:BatFile.permission -> string -> unit BatIO.output

Open the named file for writing, and return a new output channel on that file. You will need to close the file once you have finished using it.

You may use optional argument `mode` to decide whether the output will overwrite the contents of the file (by default) or to add things at the end of the file, whether the file should be created if it does not exist yet (the default) or not, whether this operation should proceed if the file exists already (the default) or not, whether the file should be opened as text (the default) or as binary, and whether the file should be opened for non-blocking operations.

You may use optional argument `perm` to specify the permissions of the file, as per Unix conventions. By default, files are created with default permissions (which depend on your setup).

Raise `Sys_error` if the file could not be opened.

    val open_out_bin : string -> unit BatIO.output

Same as `BatPervasives.open_out`, but the file is opened in binary mode, so that no translation takes place during writes. On operating systems that do not distinguish between text mode and binary mode, this function behaves like `BatPervasives.open_out` without any `mode` or `perm`.

    val open_out_gen : Pervasives.open_flag list -> int -> string -> unit BatIO.output

Deprecated.Use `open_out instead`
`open_out_gen mode perm filename` opens the named file for writing, as described above. The extra argument `mode` specifies the opening mode. The extra argument `perm` specifies the file permissions, in case the file must be created.

    val flush : unit BatIO.output -> unit

Flush the buffer associated with the given output, performing all pending writes on that channel. Interactive programs must be careful about flushing standard output and standard error at the right time.

    val output_char : unit BatIO.output -> char -> unit

Write the character on the given output channel.

    val output_string : unit BatIO.output -> string -> unit

Write the string on the given output channel.

    val output_rope : unit BatIO.output -> BatRope.t -> unit

Write the rope on the given output channel.

    val output : unit BatIO.output -> string -> int -> int -> unit

`output oc buf pos len` writes `len` characters from string `buf`, starting at offset `pos`, to the given output channel `oc`. Raise `Invalid_argument "output"` if `pos` and `len` do not designate a valid substring of `buf`.

    val output_byte : unit BatIO.output -> int -> unit

Write one 8-bit integer (as the single character with that code) on the given output channel. The given integer is taken modulo 256.

    val output_binary_int : unit BatIO.output -> int -> unit

Write one integer in binary format (4 bytes, big-endian) on the given output channel. The given integer is taken modulo 232. The only reliable way to read it back is through the `Pervasives.input_binary_int` function. The format is compatible across all machines for a given version of Objective Caml.

    val output_binary_float : unit BatIO.output -> float -> unit

Write one float in binary format (8 bytes, IEEE 754 double format) on the given output channel. The only reliable way to read it back is through the `Pervasives.input_binary_float` function. The format is compatible across all machines for a given version of Objective Caml.

    val output_value : unit BatIO.output -> 'a -> unit

Write the representation of a structured value of any type to a channel. Circularities and sharing inside the value are detected and preserved. The object can be read back, by the function `BatPervasives.input_value`. See the description of module `Marshal` for more information. `BatPervasives.output_value` is equivalent to `Marshal.output` with an empty list of flags.

    val close_out : unit BatIO.output -> unit

Close the given channel, flushing all buffered write operations. Output functions raise a `Sys_error` exception when they are applied to a closed output channel, except `close_out` and `flush`, which do nothing when applied to an already closed channel. Note that `close_out` may raise `Sys_error` if the operating system signals an error when flushing or closing.

    val close_out_noerr : unit BatIO.output -> unit

Same as `close_out`, but ignore all errors.
General input functions

    val open_in : ?mode:BatFile.open_in_flag list ->
           ?perm:BatFile.permission -> string -> BatIO.input

Open the named file for reading. You will need to close the file once you have finished using it.

You may use optional argument `mode` to decide whether the opening should fail if the file doesn't exist yet (by default) or whether the file should be created if it doesn't exist yet, whether the opening should fail if the file already exists or not (by default), whether the file should be read as binary (by default) or as text, and whether reading should be non-blocking.

You may use optional argument `perm` to specify the permissions of the file, should it be created, as per Unix conventions. By default, files are created with default permissions (which depend on your setup).

Raise `Sys_error` if the file could not be opened.

    val open_in_bin : string -> BatIO.input

Same as `Pervasives.open_in`, but the file is opened in binary mode, so that no translation takes place during reads. On operating systems that do not distinguish between text mode and binary mode, this function behaves like `Pervasives.open_in`.

    val open_in_gen : Pervasives.open_flag list -> int -> string -> BatIO.input

Deprecated.Use `open_in instead`
`open_in mode perm filename` opens the named file for reading, as described above. The extra arguments `mode` and `perm` specify the opening mode and file permissions. `Pervasives.open_in` and `Pervasives.open_in_bin` are special cases of this function.

    val input_char : BatIO.input -> char

Read one character from the given input channel. Raise `End_of_file` if there are no more characters to read.

    val input_line : BatIO.input -> string

Read characters from the given input channel, until a newline character is encountered. Return the string of all characters read, without the newline character at the end. Raise `End_of_file` if the end of the file is reached at the beginning of line.

    val input : BatIO.input -> string -> int -> int -> int

`input ic buf pos len` reads up to `len` characters from the given channel `ic`, storing them in string `buf`, starting at character number `pos`. It returns the actual number of characters read, between 0 and `len` (inclusive). A return value of 0 means that the end of file was reached. A return value between 0 and `len` exclusive means that not all requested `len` characters were read, either because no more characters were available at that time, or because the implementation found it convenient to do a partial read; `input` must be called again to read the remaining characters, if desired. (See also `Pervasives.really_input` for reading exactly `len` characters.) Exception `Invalid_argument "input"` is raised if `pos` and `len` do not designate a valid substring of `buf`.

    val really_input : BatIO.input -> string -> int -> int -> unit

`really_input ic buf pos len` reads `len` characters from channel `ic`, storing them in string `buf`, starting at character number `pos`. Raise `End_of_file` if the end of file is reached before `len` characters have been read. Raise `Invalid_argument "really_input"` if `pos` and `len` do not designate a valid substring of `buf`.

    val input_byte : BatIO.input -> int

Same as `Pervasives.input_char`, but return the 8-bit integer representing the character. Raise `End_of_file` if an end of file was reached.

    val input_binary_int : BatIO.input -> int

Read an integer encoded in binary format (4 bytes, big-endian) from the given input channel. See `Pervasives.output_binary_int`. Raise `End_of_file` if an end of file was reached while reading the integer.

    val input_binary_float : BatIO.input -> float

Read a float encoded in binary format (8 bytes, IEEE 754 double format) from the given input channel. See `Pervasives.output_binary_float`. Raise `End_of_file` if an end of file was reached while reading the float.

    val input_value : BatIO.input -> 'a

Read the representation of a structured value, as produced by `BatPervasives.output_value`, and return the corresponding value. This function is identical to `Marshal.input`; see the description of module `Marshal` for more information, in particular concerning the lack of type safety.

    val close_in : BatIO.input -> unit

Close the given channel. Input functions raise a `Sys_error` exception when they are applied to a closed input channel, except `close_in`, which does nothing when applied to an already closed channel. Note that `close_in` may raise `Sys_error` if the operating system signals an error.

    val close_in_noerr : BatIO.input -> unit

Same as `close_in`, but ignore all errors.

###### Fundamental functions and operators

    val identity : 'a -> 'a

The identity function.

    val undefined : ?message:string -> 'a -> 'b

The undefined function.

Evaluating `undefined x` always fails and raises an exception "Undefined". Optional argument `message` permits the customization of the error message.

    val (|>) : 'a -> ('a -> 'b) -> 'b

Function application. `x |> f` is equivalent to `f x`.

This operator is commonly used to write a function composition by order of evaluation (the order used in object-oriented programming) rather than by inverse order (the order typically used in functional programming).

For instance, `g (f x)` means "apply `f` to `x`, then apply `g` to the result." The corresponding notation in most object-oriented programming languages would be somewhere along the lines of `x.f.g ()`, or "starting from `x`, apply `f`, then apply `g`." In OCaml, operator ( |> ) this latest notation maps to `x |> f |> g`, or

This operator may also be useful for composing sequences of function calls without too many parenthesis.

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

Function application. `f **> x` is equivalent to `f x`.

This operators may be useful for composing sequences of function calls without too many parenthesis.

Note The name of this operator is not written in stone. It is bound to change soon.

    val (|-) : ('a -> 'b) -> ('b -> 'c) -> 'a -> 'c

Function composition. `f |- g` is `fun x -> g (f x)`. This is also equivalent to applying `<**` twice.

    val (-|) : ('a -> 'b) -> ('c -> 'a) -> 'c -> 'b

Function composition. `f -| g` is `fun x -> f (g x)`. Mathematically, this is operator o.

    val flip : ('a -> 'b -> 'c) -> 'b -> 'a -> 'c

Argument flipping.

`flip f x y` is `f y x`. Don't abuse this function, it may shorten considerably your code but it also has the nasty habit of making it harder to read.

    val ( *** ) : ('a -> 'b) -> ('c -> 'd) -> 'a * 'c -> 'b * 'd

Function pairing.

`f *** g` is `fun (x,y) -> (f x, g y)`.

    val (&&&) : ('a -> 'b) -> ('a -> 'c) -> 'a -> 'b * 'c

Applying two functions to the same argument.

`f &&& g` is `fun x -> (f x, g x)`.

    val first : ('a -> 'b) -> 'a * 'c -> 'b * 'c

Apply a function to the first element of a pair.

`first f (x, y)` is `(f x, y)`

    val second : ('a -> 'b) -> 'c * 'a -> 'c * 'b

Apply a function to the second element of a pair.

`second f (x, y)` is `(x, f y)`

    val curry : ('a * 'b -> 'c) -> 'a -> 'b -> 'c

Convert a function which accepts a pair of arguments into a function which accepts two arguments.

`curry f` is `fun x y -> f (x,y)`

    val uncurry : ('a -> 'b -> 'c) -> 'a * 'b -> 'c

Convert a function which accepts a two arguments into a function which accepts a pair of arguments.

`uncurry f` is `fun (x, y) -> f x y`

    val const : 'a -> 'b -> 'a

Ignore its second argument.

`const x` is the function which always returns `x`.

    val unique : unit -> int

Returns an unique identifier every time it is called.

Note This is thread-safe.

    val tap : ('a -> unit) -> 'a -> 'a

Allows application of a function in the middle of a pipe sequence without disturbing the sequence. `x |> tap f` evaluates to `x`, but has the side effect of `f x`. Useful for debugging.

    val finally : (unit -> unit) -> ('a -> 'b) -> 'a -> 'b

`finally fend f x` calls `f x` and then `fend()` even if `f x` raised an exception.

    val with_dispose : dispose:('a -> unit) -> ('a -> 'b) -> 'a -> 'b

`with_dispose dispose f x` invokes `f` on `x`, calling `dispose x` when `f` terminates (either with a return value or an exception).

    val args : unit -> string BatEnum.t

An enumeration of the arguments passed to this program through the command line.

`args ()` is given by the elements of `Sys.argv`, minus the first element.

    val exe : string

The name of the current executable.

`exe` is given by the first argument of `Sys.argv`

###### Enumerations

In OCaml Batteries Included, all data structures are enumerable, which means that they support a number of standard operations, transformations, etc. The general manner of enumerating the contents of a data structure is to invoke the `enum` function of your data structure.

For instance, you may use the `BatPervasives.foreach` loop to apply a function `f` to all the consecutive elements of a string `s`. For this purpose, you may write either `foreach (String.enum s) f` or `open String in foreach (enum s) f`. Either possibility states that you are enumerating through a character string `s`. Should you prefer your enumeration to proceed from the end of the string to the beginning, you may replace `String.enum` with `String.backwards`. Therefore, either `foreach (String.backwards s) f` or `open String in foreach (backwards s) f` will apply `f` to all the consecutive elements of string `s`, from the last to the first.

Similarly, you may use `List.enum` instead of `String.enum` to visit the elements of a list in the usual order, or `List.backwards` instead of `String.backwards` to visit them in the opposite order, or `Hashtbl.enum` for hash tables, etc.

More operations on enumerations are defined in module `BatEnum`, including the necessary constructors to make your own structures enumerable.

The various kinds of loops are detailed further in this documentation.

    val foreach : 'a BatEnum.t -> ('a -> unit) -> unit

Imperative loop on an enumeration.

`foreach e f` applies function `f` to each successive element of `e`. For instance, `foreach (1 -- 10) print_int` invokes function `print_int` on `1`, `2`, ..., `10`, printing `12345678910`.

Note This function is one of the many loops available on enumerations. Other commonly used loops are `BatPervasives.iter` (same usage scenario as `foreach`, but with different notations), `BatPervasives.map` (convert an enumeration to another enumeration) or `BatPervasives.fold` (flatten an enumeration by applying an operation to each element).

General-purpose loops

The following functions are the three main general-purpose loops available in OCaml. By opposition to the loops available in imperative languages, OCaml loops are regular functions, which may be passed, composed, currified, etc. In particular, each of these loops may be considered either as a manner of applying a function to a data structure or as transforming a function into another function which will act on a whole data structure.

For instance, if `f` is a function operating on one value, you may lift this function to operate on all values of an enumeration (and consequently on all values of any data structure of OCaml Batteries Included) by applying `BatPervasives.iter`, `BatPervasives.map` or `BatPervasives.fold` to this function.

    val iter : ('a -> unit) -> 'a BatEnum.t -> unit

Imperative loop on an enumeration. This loop is typically used to lift a function with an effect but no meaningful result and get it to work on enumerations.

If `f` is a function `iter f` is a function which behaves as `f` but acts upon enumerations rather than individual elements. As indicated in the type of `iter`, `f` must produce values of type `unit` (i.e. `f` has no meaningful result) the resulting function produces no meaningful result either.

In other words, `iter f` is a function which, when applied upon an enumeration `e`, calls `f` with each element of `e` in turn.

For instance, `iter f (1 -- 10)` invokes function `f` on `1`, `2`, ..., `10` and produces value `()`.

    val map : ('a -> 'b) -> 'a BatEnum.t -> 'b BatEnum.t

Transformation loop on an enumeration, used to build an enumeration from another enumeration. This loop is typically used to transform an enumeration into another enumeration with the same number of elements, in the same order.

If `f` is a function, `map f e` is a function which behaves as `f` but acts upon enumerations rather than individual elements -- and builds a new enumeration from the results of each application.

In other words, `map f` is a function which, when applied upon an enumeration containing elements `e0`, `e1`, ..., produces enumeration `f e0`, `f e1`, ...

For instance, if `odd` is the function which returns `true` when applied to an odd number or `false` when applied to an even number, `map odd (1 -- 10)` produces enumeration `true`, `false`, `true`, ..., `false`.

Similarly, if `square` is the function `fun x -> x * x`, `map square (1 -- 10)` produces the enumeration of the square numbers of all numbers between `1` and `10`.

    val filter_map : ('a -> 'b option) -> 'a BatEnum.t -> 'b BatEnum.t

Similar to a map, except that you can skip over some items of the incoming enumeration by returning None instead of Some value. Think of it as a `BatPervasives.filter` combined with a `BatPervasives.map`.

    val reduce : ('a -> 'a -> 'a) -> 'a BatEnum.t -> 'a

Transformation loop on an enumeration, used to build a single value from an enumeration.

If `f` is a function and `e` is an enumeration, `reduce f e` applies function `f` to the first two elements of `e`, then to the result of this expression and to the third element of `e`, then to the result of this new expression and to the fourth element of `e`...

In other words, `reduce f e` returns `a0` if `e` contains only one element `a0`, otherwise `f (... (f (f a0) a1) ...) aN` where `a0,a1..aN` are the elements of `e`.

    val fold : ('a -> 'b -> 'a) -> 'a -> 'b BatEnum.t -> 'a

Transformation loop on an enumeration, used to build a single value from an enumeration. This is the most powerful general-purpose loop and also the most complex.

If `f` is a function, `fold f v e` applies `f v` to the first element of `e`, then, calling `acc_1` the result of this operation, applies `f acc_1` to the second element of `e`, then, calling `acc_2` the result of this operation, applies `f acc_2` to the third element of `e`...

In other words, `fold f v e` returns `v` if `e` is empty, otherwise `f (... (f (f v a0) a1) ...) aN` where a0,a1..aN are the elements of `e`.

For instance, if `add` is the function `fun x y -> x + y`, `fold add 0` is the function which computes the sum of the elements of an enumeration. Therefore, `fold add 0 (1 -- 10)` produces result `55`.

    val scanl : ('a -> 'b -> 'a) -> 'a -> 'b BatEnum.t -> 'a BatEnum.t

Functional loop on an enumeration, used to build an enumeration from both an enumeration and an initial value. This function may be seen as a variant of `BatPervasives.fold` which returns not only the final result of `BatPervasives.fold` but the enumeration of all the intermediate results of `BatPervasives.fold`.

If `f` is a function, `scanl f v e` is applies `f v` to the first element of `e`, then, calling `acc_1` the result of this operation, applies `f acc_1` to the second element of `e`, then, calling `acc_2` the result of this operation, applies `f acc_2` to the third element of `e`...

For instance, if `add` is the function `fun x y -> x + y`, `scanl add 0` is the function which computes the sum of the elements of an enumeration. Therefore, `scanl add 0 (1 -- 10)` produces result the enumeration with elements `0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55`.

    val (/@) : 'a BatEnum.t -> ('a -> 'b) -> 'b BatEnum.t

    val (@/) : ('a -> 'b) -> 'a BatEnum.t -> 'b BatEnum.t

Mapping operators.

These operators have the same meaning as function `BatPervasives.map` but are sometimes more readable than this function, when chaining several transformations in a row.

    val (//@) : 'a BatEnum.t -> ('a -> 'b option) -> 'b BatEnum.t

    val (@//) : ('a -> 'b option) -> 'a BatEnum.t -> 'b BatEnum.t

Map combined with filter. Same as `BatPervasives.filter_map`.
Other operations on enumerations

    val exists : ('a -> bool) -> 'a BatEnum.t -> bool

`exists f e` returns `true` if there is some `x` in `e` such that `f x`

    val for_all : ('a -> bool) -> 'a BatEnum.t -> bool

`exists f e` returns `true` if for every `x` in `e`, `f x` is true

    val find : ('a -> bool) -> 'a BatEnum.t -> 'a

`find f e` returns the first element `x` of `e` such that `f x` returns `true`, consuming the enumeration up to and including the found element, or, raises `Not_found` if no such element exists in the enumeration, consuming the whole enumeration in the search.

Since `find` consumes a prefix of the enumeration, it can be used several times on the same enumeration to find the next element.

    val peek : 'a BatEnum.t -> 'a option

`peek e` returns `None` if `e` is empty or `Some x` where `x` is the next element of `e`. The element is not removed from the enumeration.

    val get : 'a BatEnum.t -> 'a option

`get e` returns `None` if `e` is empty or `Some x` where `x` is the next element of `e`, in which case the element is removed from the enumeration.

    val push : 'a BatEnum.t -> 'a -> unit

`push e x` will add `x` at the beginning of `e`.

    val junk : 'a BatEnum.t -> unit

`junk e` removes the first element from the enumeration, if any.

    val filter : ('a -> bool) -> 'a BatEnum.t -> 'a BatEnum.t

`filter f e` returns an enumeration over all elements `x` of `e` such as `f x` returns `true`.

    val (//) : 'a BatEnum.t -> ('a -> bool) -> 'a BatEnum.t

Filtering (pronounce this operator name "such that").

For instance, `(1 -- 37) // odd` is the enumeration of all odd numbers between 1 and 37.

    val concat : 'a BatEnum.t BatEnum.t -> 'a BatEnum.t

`concat e` returns an enumeration over all elements of all enumerations of `e`.

    val (--) : int -> int -> int BatEnum.t

Enumerate numbers.

`5 -- 10` is the enumeration 5,6,7,8,9,10. `10 -- 5` is the empty enumeration

    val (--^) : int -> int -> int BatEnum.t

Enumerate numbers, without the right endpoint

`5 -- 10` is the enumeration 5,6,7,8,9.

    val (--.) : float * float -> float -> float BatEnum.t

`(a, step) --. b)` creates a float enumeration from `a` to `b` with an increment of `step` between elements.

`(5.0, 1.0) --. 10.0` is the enumeration 5.0,6.0,7.0,8.0,9.0,10.0. `(10.0, -1.0) --. 5.0` is the enumeration 10.0,9.0,8.0,7.0,6.0,5.0. `(10.0, 1.0) --. 1.0` is the empty enumeration.

    val (---) : int -> int -> int BatEnum.t

As `--`, but accepts enumerations in reverse order.

`5 --- 10` is the enumeration 5,6,7,8,9,10. `10 --- 5` is the enumeration 10,9,8,7,6,5.

    val (--~) : char -> char -> char BatEnum.t

As ( -- ), but for characters.

    val print : ?first:string ->
           ?last:string ->
           ?sep:string ->
           ('a BatInnerIO.output -> 'b -> unit) ->
           'a BatInnerIO.output -> 'b BatEnum.t -> unit

Print and consume the contents of an enumeration.

###### Results

    type ('a, 'b) result = ('a, 'b) BatStd.result =

`|` | `Ok of `'a``
`|` | `Bad of `'b``

###### Thread-safety internals

Unless you are attempting to adapt Batteries Included to a new model of concurrency, you probably won't need this.

    val lock : BatConcurrent.lock Pervasives.ref

A lock used to synchronize internal operations.

By default, this is `BatConcurrent.nolock`. However, if you're using a version of Batteries compiled in threaded mode, this uses `BatMutex`. If you're attempting to use Batteries with another concurrency model, set the lock appropriately.