# Module Pervasives

    module Pervasives = struct ... end

The initially opened module.
This module provides the built-in types (numbers, booleans, strings, exceptions, references, lists, arrays, input-output channels, ...) and the basic operations over these types.
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 `Pervasives`.

Predefined types

These are predefined types :

     type int

The type of integer numbers.

     type char

The type of characters.

     type string

The type of character strings.

     type float

The type of floating-point numbers.

     type bool

The type of booleans (truth values).

     type unit = ()

The type of the unit value.

     type exn

The type of exception values.

     type 'a array

The type of arrays whose elements have type `'a`.

     type 'a list = [] | :: of 'a * 'a list

The type of lists whose elements have type `'a`.

    type 'a option = None | Some of 'a

The type of optional values.

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

The type of format strings. `'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 (see module `Printf`).

Exceptions

    val raise : exn -> 'a

Raise the given exception value
These are predefined exceptions :

    exception Match_failure of (string * int * int)

Exception raised when none of the cases of a pattern-matching apply. The arguments are the location of the pattern-matching in the source code (file name, position of first character, position of last character).

    exception Assert_failure of (string * int * int)

Exception raised when an assertion fails. The arguments are the location of the pattern-matching in the source code (file name, position of first character, position of last character).

    exception Invalid_argument of string

Exception raised by library functions to signal that the given arguments do not make sense.

    exception Failure of string

Exception raised by library functions to signal that they are undefined on the given arguments.

    exception Not_found

Exception raised by search functions when the desired object could not be found.

    exception Out_of_memory

Exception raised by the garbage collector when there is insufficient memory to complete the computation.

    exception Stack_overflow

Exception raised by the bytecode interpreter when the evaluation stack reaches its maximal size. This often indicates infinite or excessively deep recursion in the user's program.

    exception Sys_error of string

Exception raised by the input/output functions to report an operating system error.

    exception End_of_file

Exception raised by input functions to signal that the end of file has been reached.

    exception Division_by_zero

Exception raised by division and remainder operations when their second argument is null.

    exception Sys_blocked_io

A special case of `Sys_error` raised when no I/O is possible on a non-blocking I/O channel.

    exception Exit

The `Exit` exception is not raised by any library function. It is provided for use in your programs.

    val invalid_arg : string -> 'a

Raise exception `Invalid_argument` with the given string.

    val failwith : string -> 'a

Raise exception `Failure` with the given string.

Comparisons

    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 may not terminate.

    val <> : 'a -> 'a -> bool

Negation of `Pervasives.=`.

    val < : 'a -> 'a -> bool

See `Pervasives.>=`.

    val > : 'a -> 'a -> bool

See `Pervasives.>=`.

    val <= : 'a -> 'a -> bool

See `Pervasives.>=`.

    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 may not terminate.

    val compare : 'a -> 'a -> int

`compare x y` returns `0` if `x=y`, a negative integer if `x<y`, and a positive integer if `x>y`. The same restrictions as for `=` apply. `compare` can be used as the comparison function required by the `Set` and `Map` modules.

    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, it is the same as 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, except that `e1 == e2` implies `e1 = e2`.

    val != : 'a -> 'a -> bool

Negation of `Pervasives.==`.

Boolean operations

    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

Deprecated ! `Pervasives.&&` should be used instead.

    val || : bool -> bool -> bool

See `Pervasives.or`.

    val or : 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.

Integer arithmetic

Integers are 31 bits wide (or 63 bits on 64-bit processors). All operations are taken modulo 231 (or 263). They do not fail on overflow.

    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)`. If `y = 0`, `x mod y` raises `Division_by_zero`. Notice that `x mod y` is negative if `x < 0`.

    val abs : int -> int

Return the absolute value of the argument.

    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`.

Floating-point arithmetic

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.

    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 `Pervasives.atan2`.

    val sin : float -> float

See `Pervasives.atan2`.

    val tan : float -> float

See `Pervasives.atan2`.

    val acos : float -> float

See `Pervasives.atan2`.

    val asin : float -> float

See `Pervasives.atan2`.

    val atan : float -> float

See `Pervasives.atan2`.

    val atan2 : float -> float -> float

The usual trigonometric functions.

    val cosh : float -> float

See `Pervasives.tanh`.

    val sinh : float -> float

See `Pervasives.tanh`.

    val tanh : float -> float

The usual hyperbolic trigonometric functions.

    val ceil : float -> float

See `Pervasives.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 `Pervasives.float_of_int`.

    val float_of_int : int -> float

Convert an integer to floating-point.

    val truncate : float -> int

Same as `Pervasives.int_of_float`.

    val int_of_float : float -> int

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

    val max_float : float

The largest positive finite value of type `float`.

    val min_float : float

The smallest positive, non-zero, non-denormalized value of type `float`.

    val epsilon_float : float

The smallest positive float `x` such that `1.0 +. x <> 1.0`.
`type fpclass =
`

`| FP_normal` | `(* Normal number, none of the below *)`
`| FP_subnormal` | `(* Number very close to 0.0, has reduced precision *)`
`| FP_zero` | `(* Number is 0.0 or -0.0 *)`
`| FP_infinite` | `(* Number is positive or negative infinity *)`
`| FP_nan` | `(* Not a number: result of an undefined operation *)`

The five classes of floating-point numbers, as determined by the `Pervasives.classify_float` function.

    val classify_float : float -> fpclass

Return the class of the given floating-point number: normal, subnormal, zero, infinite, or not a number.

String operations

More string operations are provided in module `String`.

    val ^ : string -> string -> string

String concatenation.

Character operations

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.

Unit operations

    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.

String conversion functions

    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, octal or binary if the string begins with `0x`, `0o` or `0b` respectively. Raise `Failure "int_of_string"` if the given string is not a valid representation of an integer.

    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.

Pair operations

    val fst : 'a * 'b -> 'a

Return the first component of a pair.

    val snd : 'a * 'b -> 'b

Return the second component of a pair.

List operations

More list operations are provided in module `List`.

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

List concatenation.

Input/output

`type in_channel`
The type of input channel.
`type out_channel`
The type of output channel.

    val stdin : in_channel

The standard input for the process.

    val stdout : out_channel

The standard output for the process.

    val stderr : out_channel

The standard error ouput for the process.

Output functions 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.

    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.

Output functions on standard error

    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.

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

`type open_flag =
`

`| Open_rdonly` | `(* open for reading. *)`
`| Open_wronly` | `(* open for writing. *)`
`| Open_append` | `(* open for appending. always write at end of file (needs `Open_wronly`. *)`
`| Open_creat` | `(* create the file if it does not exist. *)`
`| Open_trunc` | `(* empty the file if it already exists. *)`
`| Open_excl` | `(* fail if the file already exists. *)`
`| Open_binary` | `(* open in binary mode (no conversion). *)`
`| Open_text` | `(* open in text mode (may perform conversions). *)`
`| Open_nonblock` | `(* open in non-blocking mode. *)`

Opening modes for `Pervasives.open_out_gen` and `Pervasives.open_in_gen`.

    val open_out : string -> out_channel

Open the named file for writing, and return a new output channel on that file, positionned at the beginning of the file. The file is truncated to zero length if it already exists. It is created if it does not already exists. Raise `Sys_error` if the file could not be opened.

    val open_out_bin : string -> out_channel

Same as `Pervasives.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 `Pervasives.open_out`.

    val open_out_gen : open_flag list -> int -> string -> out_channel

Open the named file for writing, as above. The extra argument `mode` specify the opening mode. The extra argument `perm` specifies the file permissions, in case the file must be created. `Pervasives.open_out` and `Pervasives.open_out_bin` are special cases of this function.

    val flush : out_channel -> unit

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

    val flush_all : unit -> unit

Flush all opened output channels.

    val output_char : out_channel -> char -> unit

Write the character on the given output channel.

    val output_string : out_channel -> string -> unit

Write the string on the given output channel.

    val output : out_channel -> string -> int -> int -> unit

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

    val output_byte : out_channel -> 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 : out_channel -> int -> unit

Write one integer in binary format on the given output channel. 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_value : out_channel -> '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 `Pervasives.input_value`. See the description of module `Marshal` for more information. `Pervasives.output_value` is equivalent to `Marshal.to_channel` with an empty list of flags.

    val seek_out : out_channel -> int -> unit

`seek_out chan pos` sets the current writing position to `pos` for channel `chan`. This works only for regular files. On files of other kinds (such as terminals, pipes and sockets), the behavior is unspecified.

    val pos_out : out_channel -> int

Return the current writing position for the given channel.

    val out_channel_length : out_channel -> int

Return the total length (number of characters) of the given channel. This works only for regular files. On files of other kinds, the result is meaningless.

    val close_out : out_channel -> unit

Close the given channel, flushing all buffered write operations. A `Sys_error` exception is raised if any of the functions above is called on a closed channel.

    val set_binary_mode_out : out_channel -> bool -> unit

`set_binary_mode_out oc true` sets the channel `oc` to binary mode: no translations take place during output. `set_binary_mode_out oc false` sets the channel `oc` to text mode: depending on the operating system, some translations may take place during output. For instance, under Windows, end-of-lines will be translated from `\n` to `\r\n`. This function has no effect under operating systems that do not distinguish between text mode and binary mode.

General input functions

    val open_in : string -> in_channel

Open the named file for reading, and return a new input channel on that file, positionned at the beginning of the file. Raise `Sys_error` if the file could not be opened.

    val open_in_bin : string -> in_channel

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 : open_flag list -> int -> string -> in_channel

Open the named file for reading, as 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 : in_channel -> char

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

    val input_line : in_channel -> 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 : in_channel -> string -> int -> int -> int

Read up to `len` characters from the given channel, 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 : in_channel -> string -> int -> int -> unit

Read `len` characters from the given channel, 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 : in_channel -> 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 : in_channel -> int

Read an integer encoded in binary format 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_value : in_channel -> 'a

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

    val seek_in : in_channel -> int -> unit

`seek_in chan pos` sets the current reading position to `pos` for channel `chan`. This works only for regular files. On files of other kinds, the behavior is unspecified.

    val pos_in : in_channel -> int

Return the current reading position for the given channel.

    val in_channel_length : in_channel -> int

Return the total length (number of characters) of the given channel. This works only for regular files. On files of other kinds, the result is meaningless.

    val close_in : in_channel -> unit

Close the given channel. A `Sys_error` exception is raised if any of the functions above is called on a closed channel.

    val set_binary_mode_in : in_channel -> bool -> unit

`set_binary_mode_in ic true` sets the channel `ic` to binary mode: no translations take place during input. `set_binary_mode_out ic false` sets the channel `ic` to text mode: depending on the operating system, some translations may take place during input. For instance, under Windows, end-of-lines will be translated from `\r\n` to `\n`. This function has no effect under operating systems that do not distinguish between text mode and binary mode.

References

`type `'a` ref = {
`

`mutable contents : `'a`;`

}
The type of references (mutable indirection cells) containing a value of type `'a`.

    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`.

Program termination

    val exit : int -> 'a

Flush all pending writes on `Pervasives.stdout` and `Pervasives.stderr`, and 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.) An implicit `exit 0` is performed each time a program terminates normally (but not if it terminates 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 `Pervasives.exit`. They will not be called if the program terminates 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.