• It is automatically linked with the user's object code files by the nmlc command (chapter 8).
  
  
• It is automatically ``opened'' when a compilation starts, or when the toplevel system is launched. Hence, it is possible to use unqualified identifiers to refer to the functions provided by the Pervasives module, without adding a open Pervasives directive.

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.

type float = real

The type of floating-point numbers.

type int32

Obejective Caml's int32 type (32-bit integer numbers).

type int64

Obejective Caml's int64 type (64-bit integer numbers).

type nativeint

Obejective Caml's nativeint type (native integer numbers).

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).

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 Exit

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

exception Sys_blocked_io

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

val invalid_arg: string -> 'a

Raise exception Invalid_argument with the given string.

val failwith: string -> 'a

Raise exception Failure with the given string.

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 (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.

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 succ : int -> int

succ x is x+1.

val pred : int -> int

pred x is x-1.

val abs : int -> int

Return the absolute value of the argument.

val max_int: int
val min_int: int

The greatest and smallest representable integers.

val lnot: int -> int

Bitwise logical negation.

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.

val sqrt : float -> float

Square root

val exp : float -> float
val log : float -> float
val log10 : float -> float

Exponential, natural logarithm, base 10 logarithm.

val cos : float -> float
val sin : float -> float
val tan : float -> float
val acos : float -> float
val asin : float -> float
val atan : float -> float
val atan2 : float -> float -> float

The usual trigonometric functions

val cosh : float -> float
val sinh : float -> float
val tanh : float -> float

The usual hyperbolic trigonometric functions

val ceil : float -> float
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
val float_of_int : int -> float

Convert an integer to floating-point.

val truncate : float -> int
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.

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.

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.

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. The result is unspecified if the given string is not a valid representation of a float.

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

Return the first component of a pair.

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

Return the second component of a pair.

type in_channel
type out_channel

The types of input channels and output channels.

val stdin : in_channel
val stdout : out_channel
val stderr : out_channel

The standard input, standard output, and standard error output for the process.

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.

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 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.

type open_flag =
    Open_rdonly | Open_wronly | Open_append
  | Open_creat | Open_trunc | Open_excl
  | Open_binary | Open_text | Open_nonblock

Opening modes for open_out_gen and open_in_gen.
Open_rdonly: open for reading.
Open_wronly: open for writing.
Open_append: open for appending.
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.

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 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 open_out.

val open_out_gen : mode:open_flag list -> perm: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. open_out and 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 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 -> buf:string -> pos:int -> len: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 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 input_value. See the description of module Marshal for more information. 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.

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 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 open_in.

val open_in_gen : mode:open_flag list -> perm: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. open_in and 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 -> buf:string -> pos:int -> len: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 -> buf:string -> pos:int -> len: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 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 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 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.

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.

val exit : int -> 'a

Flush all pending writes on stdout and 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 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.