`module Standard: ``Extlib.ExtPervasives.Pervasives`

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 `Standard`

.

Automatically opened module.

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

`val raise : ``exn -> 'a`

Raise the given exception value

`val invalid_arg : ``string -> 'a`

Raise exception

`Invalid_argument`

with the given string.`val failwith : ``string -> 'a`

Raise exception

`Failure`

with the given string.
**Note** This function is provided as a simple technique for
exiting a function or a program with an error message. It is
however considered a bad practice to define a library which makes
use of this function. So don't use it except for quick experiments
and for teaching.

`val exit : ``int -> 'a`

Terminate the process, returning the given status code
to the operating system: usually 0 to indicate no errors,
and a small positive integer to indicate failure.
All open output channels are flushed with

`flush_all`

.
An implicit `exit 0`

is performed each time a program
terminates normally. An implicit `exit 2`

is performed if the program
terminates early because of an uncaught exception.`val at_exit : ``(unit -> unit) -> unit`

Register the given function to be called at program
termination time. The functions registered with

`at_exit`

will be called when the program executes `Standard.exit`

,
or terminates, either normally or because of an uncaught exception.
The functions are called in ``last in, first out'' order:
the function most recently added with `at_exit`

is called first.`val (=) : ``'a -> 'a -> bool`

`e1 = e2`

tests for structural equality of `e1`

and `e2`

.
Mutable structures (e.g. references and arrays) are equal
if and only if their current contents are structurally equal,
even if the two mutable objects are not the same physical object.
Equality between functional values raises `Invalid_argument`

.
Equality between cyclic data structures does not terminate.`val (<>) : ``'a -> 'a -> bool`

Negation of

`Standard.(=)`

.`val (<) : ``'a -> 'a -> bool`

See

`Standard.(>=)`

.`val (>) : ``'a -> 'a -> bool`

See

`Standard.(>=)`

.`val (<=) : ``'a -> 'a -> bool`

See

`Standard.(>=)`

.`val (>=) : ``'a -> 'a -> bool`

Structural ordering functions. These functions coincide with
the usual orderings over integers, characters, strings
and floating-point numbers, and extend them to a
total ordering over all types.
The ordering is compatible with

`(=)`

. As in the case
of `(=)`

, mutable structures are compared by contents.
Comparison between functional values raises `Invalid_argument`

.
Comparison between cyclic structures does not terminate.`val compare : ``'a -> 'a -> int`

`compare x y`

returns `0`

if `x`

is equal to `y`

,
a negative integer if `x`

is less than `y`

, and a positive integer
if `x`

is greater than `y`

. The ordering implemented by `compare`

is compatible with the comparison predicates `=`

, `<`

and `>`

defined above, with one difference on the treatment of the float value
`Standard.nan`

. Namely, the comparison predicates treat `nan`

as different from any other float value, including itself;
while `compare`

treats `nan`

as equal to itself and less than any
other float value. This treatment of `nan`

ensures that `compare`

defines a total ordering relation.
`compare`

applied to functional values may raise `Invalid_argument`

.
`compare`

applied to cyclic structures may not terminate.

The `compare`

function can be used as the comparison function
required by the `Set.Make`

and `Map.Make`

functors, as well as
the `List.sort`

and `Array.sort`

functions.

`val min : ``'a -> 'a -> 'a`

Return the smaller of the two arguments.

`val max : ``'a -> 'a -> 'a`

Return the greater of the two arguments.

`val (==) : ``'a -> 'a -> bool`

`e1 == e2`

tests for physical equality of `e1`

and `e2`

.
On integers and characters, physical equality is identical to structural
equality. On mutable structures, `e1 == e2`

is true if and only if
physical modification of `e1`

also affects `e2`

.
On non-mutable structures, the behavior of `(==)`

is
implementation-dependent; however, it is guaranteed that
`e1 == e2`

implies `compare e1 e2 = 0`

.`val (!=) : ``'a -> 'a -> bool`

Negation of

`Standard.(==)`

.`val not : ``bool -> bool`

The boolean negation.

`val (&&) : ``bool -> bool -> bool`

The boolean ``and''. Evaluation is sequential, left-to-right:
in

`e1 && e2`

, `e1`

is evaluated first, and if it returns `false`

,
`e2`

is not evaluated at all.`val (&) : ``bool -> bool -> bool`

`val (||) : ``bool -> bool -> bool`

The boolean ``or''. Evaluation is sequential, left-to-right:
in

`e1 || e2`

, `e1`

is evaluated first, and if it returns `true`

,
`e2`

is not evaluated at all.
Integers are 31 bits wide (or 63 bits on 64-bit processors).
All operations are taken modulo 2^{31} (or 2^{63}).

**Note** These operations do not fail on overflow. In other words,
although `Standard.max_int`

is the largest possible integer, addition
`max_int + 1`

will succeed. However, the result if this addition
is `min_int`

. If you wish your operations to fail on overflow,
open module `Data.Numeric.SafeInt`

.

More operations on integers are defined in `Int`

, `SafeInt`

,
`Int32`

, `Int64`

and `Native_int`

.

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

Unary negation. You can also write

`-e`

instead of `~-e`

.`val succ : ``int -> int`

`succ x`

is `x+1`

.`val pred : ``int -> int`

`pred x`

is `x-1`

.`val (+) : ``int -> int -> int`

Integer addition.

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

Integer subtraction.

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

Integer multiplication.

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

Integer division.
Raise

`Division_by_zero`

if the second argument is 0.
Integer division rounds the real quotient of its arguments towards zero.
More precisely, if `x >= 0`

and `y > 0`

, `x / y`

is the greatest integer
less than or equal to the real quotient of `x`

by `y`

. Moreover,
`(-x) / y = x / (-y) = -(x / y)`

.`val mod : ``int -> int -> int`

Integer remainder. If

`y`

is not zero, the result
of `x mod y`

satisfies the following properties:
`x = (x / y) * y + x mod y`

and
`abs(x mod y) <= abs(y)-1`

.
If `y = 0`

, `x mod y`

raises `Division_by_zero`

.
Notice that `x mod y`

is nonpositive if and only if `x < 0`

.
Raise `Division_by_zero`

if `y`

is zero.`val abs : ``int -> int`

Return the absolute value of the argument. Note that this may be
negative if the argument is

`min_int`

.`val max_int : ``int`

The greatest representable integer.

`val min_int : ``int`

The smallest representable integer.

Bitwise operations

`val land : ``int -> int -> int`

Bitwise logical and.

`val lor : ``int -> int -> int`

Bitwise logical or.

`val lxor : ``int -> int -> int`

Bitwise logical exclusive or.

`val lnot : ``int -> int`

Bitwise logical negation.

`val lsl : ``int -> int -> int`

`n lsl m`

shifts `n`

to the left by `m`

bits.
The result is unspecified if `m < 0`

or `m >= bitsize`

,
where `bitsize`

is `32`

on a 32-bit platform and
`64`

on a 64-bit platform.`val lsr : ``int -> int -> int`

`n lsr m`

shifts `n`

to the right by `m`

bits.
This is a logical shift: zeroes are inserted regardless of
the sign of `n`

.
The result is unspecified if `m < 0`

or `m >= bitsize`

.`val asr : ``int -> int -> int`

`n asr m`

shifts `n`

to the right by `m`

bits.
This is an arithmetic shift: the sign bit of `n`

is replicated.
The result is unspecified if `m < 0`

or `m >= bitsize`

.
Caml's floating-point numbers follow the
IEEE 754 standard, using double precision (64 bits) numbers.
Floating-point operations never raise an exception on overflow,
underflow, division by zero, etc. Instead, special IEEE numbers
are returned as appropriate, such as `infinity`

for `1.0 /. 0.0`

,
`neg_infinity`

for `-1.0 /. 0.0`

, and `nan`

(``not a number'')
for `0.0 /. 0.0`

. These special numbers then propagate through
floating-point computations as expected: for instance,
`1.0 /. infinity`

is `0.0`

, and any operation with `nan`

as
argument returns `nan`

as result.

More floating-point operations are defined in `Float`

.

`val (~-.) : ``float -> float`

Unary negation. You can also write

`-.e`

instead of `~-.e`

.`val (+.) : ``float -> float -> float`

Floating-point addition

`val (-.) : ``float -> float -> float`

Floating-point subtraction

`val (*.) : ``float -> float -> float`

Floating-point multiplication

`val (/.) : ``float -> float -> float`

Floating-point division.

`val (**) : ``float -> float -> float`

Exponentiation

`val sqrt : ``float -> float`

Square root

`val exp : ``float -> float`

Exponential.

`val log : ``float -> float`

Natural logarithm.

`val log10 : ``float -> float`

Base 10 logarithm.

`val cos : ``float -> float`

See

`Standard.atan2`

.`val sin : ``float -> float`

See

`Standard.atan2`

.`val tan : ``float -> float`

See

`Standard.atan2`

.`val acos : ``float -> float`

See

`Standard.atan2`

.`val asin : ``float -> float`

See

`Standard.atan2`

.`val atan : ``float -> float`

See

`Standard.atan2`

.`val atan2 : ``float -> float -> float`

The usual trigonometric functions.

`val cosh : ``float -> float`

See

`Standard.tanh`

.`val sinh : ``float -> float`

See

`Standard.tanh`

.`val tanh : ``float -> float`

The usual hyperbolic trigonometric functions.

`val ceil : ``float -> float`

See

`Standard.floor`

.`val floor : ``float -> float`

Round the given float to an integer value.

`floor f`

returns the greatest integer value less than or
equal to `f`

.
`ceil f`

returns the least integer value greater than or
equal to `f`

.`val abs_float : ``float -> float`

Return the absolute value of the argument.

`val mod_float : ``float -> float -> float`

`mod_float a b`

returns the remainder of `a`

with respect to
`b`

. The returned value is `a -. n *. b`

, where `n`

is the quotient `a /. b`

rounded towards zero to an integer.`val frexp : ``float -> float * int`

`frexp f`

returns the pair of the significant
and the exponent of `f`

. When `f`

is zero, the
significant `x`

and the exponent `n`

of `f`

are equal to
zero. When `f`

is non-zero, they are defined by
`f = x *. 2 ** n`

and `0.5 <= x < 1.0`

.`val ldexp : ``float -> int -> float`

`ldexp x n`

returns `x *. 2 ** n`

.`val modf : ``float -> float * float`

`modf f`

returns the pair of the fractional and integral
part of `f`

.`val float : ``int -> float`

Same as

`Standard.float_of_int`

.`val float_of_int : ``int -> float`

Convert an integer to floating-point.

`val truncate : ``float -> int`

Same as

`Standard.int_of_float`

.`val int_of_float : ``float -> int`

Truncate the given floating-point number to an integer.
The result is unspecified if the argument is

`nan`

or falls outside the
range of representable integers.`val infinity : ``float`

Positive infinity.

`val neg_infinity : ``float`

Negative infinity.

`val nan : ``float`

A special floating-point value denoting the result of an
undefined operation such as

`0.0 /. 0.0`

. Stands for
``not a number''. Any floating-point operation with `nan`

as
argument returns `nan`

as result. As for floating-point comparisons,
`=`

, `<`

, `<=`

, `>`

and `>=`

return `false`

and `<>`

returns `true`

if one or both of their arguments is `nan`

.
More string operations are provided in module `String`

.

`val (^) : ``string -> string -> string`

String concatenation.

`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.

More character operations are provided in module `Char`

.

`val int_of_char : ``char -> int`

Return the ASCII code of the argument.

`val char_of_int : ``int -> char`

Return the character with the given ASCII code.
Raise

`Invalid_argument "char_of_int"`

if the argument is
outside the range 0--255.
More unit operations are provided in module `Unit`

`val ignore : ``'a -> unit`

Discard the value of its argument and return

`()`

.
For instance, `ignore(f x)`

discards the result of
the side-effecting function `f`

. It is equivalent to
`f x; ()`

, except that the latter may generate a
compiler warning; writing `ignore(f x)`

instead
avoids the warning.
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 string_of_bool : ``bool -> string`

Return the string representation of a boolean.

`val bool_of_string : ``string -> bool`

Convert the given string to a boolean.
Raise

`Invalid_argument "bool_of_string"`

if the string is not
`"true"`

or `"false"`

.`val string_of_int : ``int -> string`

Return the string representation of an integer, in decimal.

`val int_of_string : ``string -> int`

Convert the given string to an integer.
The string is read in decimal (by default) or in hexadecimal (if it
begins with

`0x`

or `0X`

), octal (if it begins with `0o`

or `0O`

),
or binary (if it begins with `0b`

or `0B`

).
Raise `Failure "int_of_string"`

if the given string is not
a valid representation of an integer, or if the integer represented
exceeds the range of integers representable in type `int`

.`val string_of_float : ``float -> string`

Return the string representation of a floating-point number.

`val float_of_string : ``string -> float`

Convert the given string to a float. Raise

`Failure "float_of_string"`

if the given string is not a valid representation of a float.`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.

More list operations are provided in module `List`

.

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

List concatenation.

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

and `File`

.

`val stdin : ``IO.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 IO.output`

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

Use this output to display regular messages.

`val stderr : ``unit IO.output`

Standard error output, as per Unix/Windows conventions.

Use this output to display warnings and error messages.

`val stdnull : ``unit IO.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_char : ``char -> unit`

Print a character on standard output.

`val print_string : ``string -> unit`

Print a string on standard output.

`val print_int : ``int -> unit`

Print an integer, in decimal, on standard output.

`val print_float : ``float -> unit`

Print a floating-point number, in decimal, on standard output.

`val print_endline : ``string -> unit`

Print a string, followed by a newline character, on
standard output and flush standard output.

`val print_newline : ``unit -> unit`

Print a newline character on standard output, and flush
standard output. This can be used to simulate line
buffering of standard output.

`val print_guess : ``'a -> unit`

Attempt to print the representation of a runtime value on the
standard output. See remarks for

`Standard.dump`

. This function is
useful mostly for debugging. As a general rule, it should not be
used in production code.`val print_all : ``IO.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_char : ``char -> unit`

Print a character on standard error.

`val prerr_string : ``string -> unit`

Print a string on standard error.

`val prerr_int : ``int -> unit`

Print an integer, in decimal, on standard error.

`val prerr_float : ``float -> unit`

Print a floating-point number, in decimal, on standard error.

`val prerr_endline : ``string -> unit`

Print a string, followed by a newline character on standard error
and flush standard error.

`val prerr_newline : ``unit -> unit`

Print a newline character on standard error, and flush
standard error.

`val prerr_guess : ``'a -> unit`

Attempt to print the representation of a runtime value on the
error output. See remarks for

`Standard.dump`

. This function is
useful mostly for debugging.`val prerr_all : ``IO.input -> unit`

Print the contents of an input to the error output.

Input functions on standard input

`val read_line : ``unit -> string`

Flush standard output, then read characters from standard input
until a newline character is encountered. Return the string of
all characters read, without the newline character at the end.

`val read_int : ``unit -> int`

Flush standard output, then read one line from standard input
and convert it to an integer. Raise

`Failure "int_of_string"`

if the line read is not a valid representation of an integer.`val read_float : ``unit -> float`

Flush standard output, then read one line from standard input
and convert it to a floating-point number.
The result is unspecified if the line read is not a valid
representation of a floating-point number.

General output functions

`val open_out : ``?mode:File.open_out_flag list ->`

?perm:File.permission -> string -> unit IO.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 IO.output`

Same as

`Standard.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 `Standard.open_out`

without any
`mode`

or `perm`

.`val open_out_gen : ``open_flag list -> int -> string -> unit IO.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 IO.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 IO.output -> char -> unit`

Write the character on the given output channel.

`val output_string : ``unit IO.output -> string -> unit`

Write the string on the given output channel.

`val output_rope : ``unit IO.output -> Rope.t -> unit`

Write the rope on the given output channel.

`val output : ``unit IO.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 IO.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 IO.output -> int -> unit`

Write one integer in binary format (4 bytes, big-endian)
on the given output channel.
The given integer is taken modulo 2^{32}.
The only reliable way to read it back is through the

`Standard.input_binary_int`

function. The format is compatible across
all machines for a given version of Objective Caml.`val output_value : ``unit IO.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

`Standard.input_value`

. See the description of module
`Marshal`

for more information. `Standard.output_value`

is equivalent
to `Marshal.output`

with an empty list of flags.`val close_out : ``unit IO.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 IO.output -> unit`

Same as

`close_out`

, but ignore all errors.General input functions

`val open_in : ``?mode:File.open_in_flag list ->`

?perm:File.permission -> string -> IO.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 -> IO.input`

Same as

`Standard.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 `Standard.open_in`

.`val open_in_gen : ``open_flag list -> int -> string -> IO.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.
`Standard.open_in`

and `Standard.open_in_bin`

are special
cases of this function.`val input_char : ``IO.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 : ``IO.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 : ``IO.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 `Standard.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 : ``IO.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 : ``IO.input -> int`

Same as

`Standard.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 : ``IO.input -> int`

Read an integer encoded in binary format (4 bytes, big-endian)
from the given input channel. See

`Standard.output_binary_int`

.
Raise `End_of_file`

if an end of file was reached while reading the
integer.`val input_value : ``IO.input -> 'a`

Read the representation of a structured value, as produced
by

`Standard.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 : ``IO.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 : ``IO.input -> unit`

Same as

`close_in`

, but ignore all errors.
More operations on references are defined in module `Ref`

.

`val ref : ``'a -> 'a ref`

Return a fresh reference containing the given value.

`val (!) : ``'a ref -> 'a`

`!r`

returns the current contents of reference `r`

.
Equivalent to `fun r -> r.contents`

.`val (:=) : ``'a ref -> 'a -> unit`

`r := a`

stores the value of `a`

in reference `r`

.
Equivalent to `fun r v -> r.contents <- v`

.`val incr : ``int ref -> unit`

Increment the integer contained in the given reference.
Equivalent to

`fun r -> r := succ !r`

.`val decr : ``int ref -> unit`

Decrement the integer contained in the given reference.
Equivalent to

`fun r -> r := pred !r`

.type`('a, 'b, 'c, 'd)`

format4 =`('a, 'b, 'c, 'c, 'c, 'd) format6`

type`('a, 'b, 'c)`

format =`('a, 'b, 'c, 'c) format4`

Simplified type for format strings, included for backward compatibility
with earlier releases of Objective Caml.

`'a`

is the type of the parameters of the format,
`'c`

is the result type for the "printf"-style function,
and `'b`

is the type of the first argument given to
`%a`

and `%t`

printing functions.`val string_of_format : ``('a, 'b, 'c, 'd, 'e, 'f) format6 -> string`

Converts a format string into a string.

`val format_of_string : ``('a, 'b, 'c, 'd, 'e, 'f) format6 -> ('a, 'b, 'c, 'd, 'e, 'f) format6`

`format_of_string s`

returns a format string read from the string
literal `s`

.`val (^^) : ``('a, 'b, 'c, 'd, 'e, 'f) format6 ->`

('f, 'b, 'c, 'e, 'g, 'h) format6 -> ('a, 'b, 'c, 'd, 'g, 'h) format6

`f1 ^^ f2`

catenates formats `f1`

and `f2`

. The result is a format
that accepts arguments from `f1`

, then arguments from `f2`

.`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 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 args : ``unit -> string Enum.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`

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 `Standard.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 `Enum`

,
including the necessary constructors to make your own structures
enumerable.

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

`val foreach : ``'a Enum.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 `Standard.iter`

(same usage
scenario as `foreach`

, but with different notations), `Standard.map`

(convert an enumeration to another enumeration) or `Standard.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 `Standard.iter`

, `Standard.map`

or `Standard.fold`

to this function.

`val iter : ``('a -> unit) -> 'a Enum.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 Enum.t -> 'b Enum.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 `e1`

, `e2`

, ...,
produces enumeration `f e1`

, `f e2`

, ...

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 reduce : ``('a -> 'a -> 'a) -> 'a Enum.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, `fold f e`

returns `a_1`

if `e`

contains only
one element, otherwise `f (... (f (f a1) a2) ...) aN`

where
a1..N are the elements of `e`

.

`val fold : ``('a -> 'b -> 'a) -> 'a -> 'b Enum.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 a1) a2) ...) aN`

where a1..N 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 Enum.t -> 'a Enum.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

`Standard.fold`

which returns not only the final
result of `Standard.fold`

but the enumeration of all the intermediate
results of `Standard.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 Enum.t -> ('a -> 'b) -> 'b Enum.t`

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

Mapping operators.

These operators have the same meaning as function `Standard.map`

but are
sometimes more readable than this function, when chaining
several transformations in a row.

Other operations on enumerations

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

`exists f e`

returns `true`

if there is some `x`

in `e`

such
that `f x`

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

`exists f e`

returns `true`

if for every `x`

in `e`

, `f x`

is true`val find : ``('a -> bool) -> 'a Enum.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 Enum.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 Enum.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 Enum.t -> 'a -> unit`

`push e x`

will add `x`

at the beginning of `e`

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

`junk e`

removes the first element from the enumeration, if any.`val filter : ``('a -> bool) -> 'a Enum.t -> 'a Enum.t`

`filter f e`

returns an enumeration over all elements `x`

of `e`

such
as `f x`

returns `true`

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

`concat e`

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

.`val (--) : ``int -> int -> int Enum.t`

Enumerate numbers.

`5 -- 10`

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

is the empty enumeration

`val (--.) : ``float * float -> float -> float Enum.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 Enum.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 Enum.t`

As ( -- ), but for characters.

`val print : ``?first:string ->`

?last:string ->

?sep:string ->

('a Extlib.InnerIO.output -> 'b -> unit) ->

'a Extlib.InnerIO.output -> 'b Enum.t -> unit

Print and consume the contents of an enumeration.

type`('a, 'b)`

result =`('a, 'b) Extlib.Std.result`

=

`|` |
`Ok of ` |

`|` |
`Bad of ` |

`val sexp_of_result : ``('a -> Sexplib.Sexp.t) ->`

('b -> Sexplib.Sexp.t) ->

('a, 'b) result -> Sexplib.Sexp.t

`val result_of_sexp : ``(Sexplib.Sexp.t -> 'a) ->`

(Sexplib.Sexp.t -> 'b) ->

Sexplib.Sexp.t -> ('a, 'b) result

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

`val lock : ``Concurrency.lock ref`

A lock used to synchronize internal operations.

By default, this is `Concurrency.nolock`

. However, if you're using a version
of Batteries compiled in threaded mode, this uses `Threads.Mutex`

. If you're attempting
to use Batteries with another concurrency model, set the lock appropriately.