Module Pervasives


structure Pervasives = struct ... end
This module is special in two ways: 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 that cannot be re-defined: 
 type int
The type of integer numbers. 
 type char
The type of characters. 
 type string
The type of character strings. 
 type real (float)
The type of real numbers (floating-point numbers). 
 type bool = True (true) | False (false)
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 = [] (Nil, nil) | :: 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. It can be re-defined.


Exceptions

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
val > : 'a -> 'a -> bool
val <= : 'a -> 'a -> bool
val >= : 'a -> 'a -> bool
Structural ordering functions. These functions coincide with the usual orderings over integers, characters, strings and real 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.


Boolean operations 


val not : bool -> bool
The boolean negation.
val && (andalso): 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 || (orelse): 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. 
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 % y satisfies the following properties: x = (x / y) * y + x % y and abs(x % y) < abs(y). If y = 0, x % y raises Division_by_zero. Note that x % y is negative if x < 0. Note that % is an infix operator and mod is a prefix operator. 
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 << 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 >> 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
asr n 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.


Real arithmetic

Caml's real numbers follow the IEEE 754 standard, using double precision (64 bits) numbers. real 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 real computations as expected: for instance, 1.0 /. infinity is 0.0, and any operation with nan as argument returns nan as result.

val - : real -> real
Unary negation. 
val + : real -> real -> real 
val - : real -> real -> real 
val * : real -> real -> real 
val / : real -> real -> real
Real addition, substraction, multiplication and division.
val ** : real -> real -> real
Exponentiation
val sqrt : real -> real
Square root
val exp : real -> real
Exponential.
val log : real -> real
Natural logarithm.
val log10 : real -> real
Base 10 logarithm.
val cos : real -> real
val sin : real -> real
val tan : real -> real
val acos : real -> real
val asin : real -> real
val atan : real -> real
val atan2 : real -> real
The usual trigonometric functions.
val cosh : real -> real
val sinh : real -> real
val tanh : real -> real
The usual hyperbolic trigonometric functions.
val ceil : real -> real
val floor : real -> real
Round the given real value 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_real (abs_float): real -> real
Return the absolute value of the argument.
val mod_real (mod_float): real -> real -> real
mod_real 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 : real -> real * 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 : real -> int -> real
ldexp x n returns x *. 2 ** n.
val modf : real -> real * real
modf f returns the pair of the fractional and integral part of f.
val real_of_int (float_of_int, float) : int -> real
Convert an integer to real.
val int_of_real (int_of_real, truncate): real -> int
Truncate the given real number to an integer. The result is unspecified if it falls outside the range of representable integers.
val infinity : real
Positive infinity.
val neg_infinity : real
Negative infinity.
val nan : real
A special real value denoting the result of an undefined operation such as 0.0 /. 0.0. Stands for "not a number".
val max_real (max_float) : real
The largest positive finite value of type real.
val min_real (min_float) : real
The smallest positive, non-zero, non-denormalized value of type real.
val epsilon_real (epsilon_float) : real
The smallest positive real 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 real numbers, as determined by the Pervasives.classify_real function.

val classify_real (classify_float) : real -> fpclass
Return the class of the given real 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_real (string_of_float) : real -> string
Return the string representation of a real number.
val real_of_string (float_of_string) : string -> real
Convert the given string to a real. Raise Failure "float_of_string" if the given string is not a valid representation of a real.


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.


References 


type 'a ref
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. 
val := : 'a ref -> 'a -> unit
r := a stores the value of a in reference r. 
val ++, -- : int ref -> unit
val ++, -- : real ref -> unit
val incr : int ref -> unit
val decr : int ref -> unit
Increment/decrement the integer (or real number) contained in the given reference. ++ and -- are postfix operators. 
val +=, -=, *=, /= :  int ref -> int -> unit
val +=, -=, *=, /= :  real ref -> real -> unit
x += i increases the integer contained in x by i.


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_real (print_float) : real -> unit
Print a real 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_real (prerr_float) : real -> unit
Print a real 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_real (read_float) : unit -> real
Flush standard output, then read one line from standard input and convert it to a real number. The result is unspecified if the line read is not a valid representation of a real 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.


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.