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NAME

       Pervasives - The initially opened module.

Module

       Module   Pervasives

Documentation

       Module Pervasives
        : sig end

       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
       Pervasives .

       === Exceptions ===

       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.

       exception Exit

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

       === 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 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 Pervasives.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.   The  result  is unspecified if one of the
       arguments contains the float value nan .

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

       Return the greater of the two  arguments.   The  result  is  unspecified  if  one  of  the
       arguments contains the float value nan .

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

       e1  == e2 tests for physical equality of e1 and e2 .  On mutable types such as references,
       arrays, strings, records with mutable fields and objects with mutable instance  variables,
       e1  ==  e2  is  true  if  and  only  if  physical modification of e1 also affects e2 .  On
       non-mutable types, the behavior  of  (==)  is  implementation-dependent;  however,  it  is
       guaranteed that e1 == e2 implies compare e1 e2 = 0 .

       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

       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.

       val (or) : bool -> bool -> bool

       Deprecated.

       Pervasives.(||) should be used instead.

       === Integer arithmetic ===

       === Integers are 31 bits wide (or 63 bits on 64-bit processors).  All operations are taken
       modulo 2^{31} (or 2^{63}).  They do not fail on overflow. ===

       val (~-) : int -> int

       Unary negation. You can also write - e instead of ~- e .

       val (~+) : int -> int

       Unary addition. You can also write + e instead of ~+ e .

       Since 3.12.0

       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  .   Note  that  x  mod  y  is  negative  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 .

       === 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
       arithmetic 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

       Unary addition. You can also write +. e instead of ~+. e .

       Since 3.12.0

       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 expm1 : float -> float

       expm1 x computes exp x -. 1.0 , giving numerically-accurate results even if x is close  to
       0.0 .

       Since 3.12.0

       val log1p : float -> float

       log1p  x  computes  log(1.0 +. x) (natural logarithm), giving numerically-accurate results
       even if x is close to 0.0 .

       Since 3.12.0

       val cos : float -> float

       Cosine.  Argument is in radians.

       val sin : float -> float

       Sine.  Argument is in radians.

       val tan : float -> float

       Tangent.  Argument is in radians.

       val acos : float -> float

       Arc cosine.  The argument must fall within the range [-1.0, 1.0] .  Result is  in  radians
       and is between 0.0 and pi .

       val asin : float -> float

       Arc sine.  The argument must fall within the range [-1.0, 1.0] .  Result is in radians and
       is between -pi/2 and pi/2 .

       val atan : float -> float

       Arc tangent.  Result is in radians and is between -pi/2 and pi/2 .

       val atan2 : float -> float -> float

       atan2 y x returns the arc tangent of y /. x .  The signs of x and y are used to  determine
       the quadrant of the result.  Result is in radians and is between -pi and pi .

       val cosh : float -> float

       Hyperbolic cosine.  Argument is in radians.

       val sinh : float -> float

       Hyperbolic sine.  Argument is in radians.

       val tanh : float -> float

       Hyperbolic tangent.  Argument is in radians.

       val ceil : float -> float

       Round  above  to an integer value.  ceil f returns the least integer value greater than or
       equal to f .  The result is returned as a float.

       val floor : float -> float

       Round below to an integer value.  floor f returns the greatest integer value less than  or
       equal to f .  The result is returned as a float.

       val abs_float : float -> float

       abs_float f returns the absolute value of f .

       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  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 .

       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 difference between 1.0 and the smallest exactly  representable  floating-point  number
       greater than 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 (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.

       === 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 output 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  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.

       === 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. *)
        | Open_creat  (* create the file if it does not exist. *)
        | Open_trunc  (* empty the file if it already exists. *)
        | Open_excl  (* fail if Open_creat and 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_out_gen mode perm filename opens the named file for writing, as described 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 open output channels; ignore errors.

       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

       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 : 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 (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
       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.  Does not work on channels
       opened with the Open_append flag (returns unspecified results).

       val out_channel_length : out_channel -> int

       Return the size (number of characters) of the regular file on which the given  channel  is
       opened.   If  the  channel  is  opened on a file that is not a regular file, the result is
       meaningless.

       val close_out : out_channel -> 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 : out_channel -> unit

       Same as close_out , but ignore all errors.

       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_in_gen 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 : 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

       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 : in_channel -> 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 : 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  (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_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  size (number of characters) of the regular file on which the given channel is
       opened.  If the channel is opened on a file that is not a  regular  file,  the  result  is
       meaningless.   The  returned  size does not take into account the end-of-line translations
       that can be performed when reading from a channel opened in text mode.

       val close_in : in_channel -> 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 : in_channel -> unit

       Same as close_in , but ignore all errors.

       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.

       === Operations on large files ===

       module LargeFile : sig end

       Operations  on  large  files.   This  sub-module  provides  64-bit variants of the channel
       functions that manipulate file positions and file sizes.  By  representing  positions  and
       sizes  by  64-bit  integers  (type  int64 ) instead of regular integers (type int ), these
       alternate functions allow operating on files whose sizes are greater than max_int .

       === 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 .

       === Operations on format strings ===

       === Format strings are used to read and print data  using  formatted  input  functions  in
       module Scanf and formatted output in modules Printf and Format. ===

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

       Format strings have a general and highly polymorphic type ('a, 'b, 'c, 'd, 'e, 'f) format6
       . Type format6 is built in.  The two  simplified  types,  format  and  format4  below  are
       included  for  backward  compatibility with earlier releases of Objective Caml.  'a is the
       type of the parameters of the format, 'b is the type of the first argument given to %a and
       %t printing functions, 'c is the type of the argument transmitted to the first argument of
       "kprintf"-style functions, 'd is the result type for the "scanf"-style  functions,  'e  is
       the  type  of the receiver function for the "scanf"-style functions, 'f is the result type
       for the "printf"-style function.

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

       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 .

       === Program termination ===

       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  Pervasives.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.