Chapter 23 The core library

This chapter describes the OCaml core library, which iscomposed of declarations for built-in types and exceptions, plusthe module Pervasives that provides basic operations on thesebuilt-in types. The Pervasives module is special in twoways:

  • It is automatically linked with the user’s object code files bythe ocamlc command (chapter 9).
  • It is automatically “opened” when a compilation starts, orwhen the toplevel system is launched. Hence, it is possible to useunqualified identifiers to refer to the functions provided by thePervasives module, without adding a open Pervasives directive.

Conventions

The declarations of the built-in types and the components of modulePervasives are printed one by one in typewriter font, followed by ashort comment. All library modules and the components they provide areindexed at the end of this report.

23.1 Built-in types and predefined exceptions

The following built-in types and predefined exceptions are alwaysdefined in thecompilation environment, but are not part of any module. As aconsequence, they can only be referred by their short names.

Built-in types

  1.  type int

The type of integer numbers.
  1.  type char

The type of characters.
  1.  type bytes

The type of (writable) byte sequences.
  1.  type string

The type of (read-only) character strings.
  1.  type float

The type of floating-point numbers.
  1.  type bool = false | true

The type of booleans (truth values).
  1.  type unit = ()

The type of the unit value.
  1.  type exn

The type of exception values.
  1.  type 'a array

The type of arrays whose elements have type 'a.
  1.  type 'a list = [] | :: of 'a * 'a list

The type of lists whose elements have type 'a.
  1. type 'a option = None | Some of 'a

The type of optional values of type 'a.
  1. type int32

The type of signed 32-bit integers.Literals for 32-bit integers are suffixed by l.See the Int32[Int32] module.
  1. type int64

The type of signed 64-bit integers.Literals for 64-bit integers are suffixed by L.See the Int64[Int64] module.
  1. type nativeint

The type of signed, platform-native integers (32 bits on 32-bitprocessors, 64 bits on 64-bit processors).Literals for native integers are suffixed by n.See the Nativeint[Nativeint] module.
  1. type ('a, 'b, 'c, 'd, 'e, 'f) format6

The type of format strings. 'a is the type of the parameters ofthe format, 'f is the result type for the printf-stylefunctions, 'b is the type of the first argument given to %a and%t printing functions (see module Printf[Printf]),'c is the result type of these functions, and also the type of theargument transmitted to the first argument of kprintf-stylefunctions, 'd is the result type for the scanf-style functions(see module Scanf[Scanf]),and 'e is the type of the receiver function for the scanf-stylefunctions.
  1. type 'a lazy_t

This type is used to implement the Lazy[Lazy] module.It should not be used directly.

Predefined exceptions

  1. exception Match_failure of (string * int * int)

Exception raised when none of the cases of a pattern-matchingapply. The arguments are the location of the match keywordin the source code (file name, line number, column number).
  1. exception Assert_failure of (string * int * int)

Exception raised when an assertion fails. The arguments arethe location of the assert keyword in the source code(file name, line number, column number).
  1. exception Invalid_argument of string

Exception raised by library functions to signal that the givenarguments do not make sense. The string gives some informationto the programmer. As a general rule, this exception should notbe caught, it denotes a programming error and the code should bemodified not to trigger it.
  1. exception Failure of string

Exception raised by library functions to signal that they areundefined on the given arguments. The string is meant to give someinformation to the programmer; you must not pattern match onthe string literal because it may change in future versions (useFailure _ instead).
  1. exception Not_found

Exception raised by search functions when the desired objectcould not be found.
  1. exception Out_of_memory

Exception raised by the garbage collectorwhen there is insufficient memory to complete the computation.
  1. exception Stack_overflow

Exception raised by the bytecode interpreter when the evaluationstack reaches its maximal size. This often indicates infiniteor excessively deep recursion in the user’s program.(Not fully implemented by the native-code compiler;see section 12.5.)
  1. exception Sys_error of string

Exception raised by the input/output functions to report anoperating system error. The string is meant to give someinformation to the programmer; you must not pattern match onthe string literal because it may change in future versions (useSyserror instead).
  1. exception End_of_file

Exception raised by input functions to signal that theend of file has been reached.
  1. exception Division_by_zero

Exception raised by integer division and remainder operationswhen their second argument is zero.
  1. exception Sys_blocked_io

A special case of Sys_error raised when no I/O is possibleon a non-blocking I/O channel.
  1. exception Undefined_recursive_module of (string * int * int)

Exception raised when an ill-founded recursive module definitionis evaluated. (See section 8.2.)The arguments are the location of the definition in the source code(file name, line number, column number).

23.2 Module Stdlib: the initially opened module

23.3 Module Stdlib : The OCaml Standard library.

This module is automatically opened at the beginning of eachcompilation. All components of this module can therefore bereferred by their short name, without prefixing them by Stdlib.

It particular, it provides the basic operations over the built-in types(numbers, booleans, byte sequences, strings, exceptions, references,lists, arrays, input-output channels, …).

Exceptions

  1. val raise : exn -> 'a

Raise the given exception value

  1. val raise_notrace : exn -> 'a

A faster version raise which does not record the backtrace.

Since: 4.02.0

  1. val invalid_arg : string -> 'a

Raise exception Invalid_argument with the given string.

  1. val failwith : string -> 'a

Raise exception Failure with the given string.

  1. exception Exit

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

  1. exception Match_failure of (string * int * int)

Exception raised when none of the cases of a pattern-matchingapply. The arguments are the location of the match keyword in thesource code (file name, line number, column number).

  1. exception Assert_failure of (string * int * int)

Exception raised when an assertion fails. The arguments are thelocation of the assert keyword in the source code (file name, linenumber, column number).

  1. exception Invalid_argument of string

Exception raised by library functions to signal that the givenarguments do not make sense. The string gives some information tothe programmer. As a general rule, this exception should not becaught, it denotes a programming error and the code should bemodified not to trigger it.

  1. exception Failure of string

Exception raised by library functions to signal that they areundefined on the given arguments. The string is meant to give someinformation to the programmer; you must not pattern match on thestring literal because it may change in future versions (useFailure _ instead).

  1. exception Not_found

Exception raised by search functions when the desired object couldnot be found.

  1. exception Out_of_memory

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

  1. exception Stack_overflow

Exception raised by the bytecode interpreter when the evaluationstack reaches its maximal size. This often indicates infinite orexcessively deep recursion in the user’s program. (Not fullyimplemented by the native-code compiler.)

  1. exception Sys_error of string

Exception raised by the input/output functions to report anoperating system error. The string is meant to give someinformation to the programmer; you must not pattern match on thestring literal because it may change in future versions (useSyserror instead).

  1. exception End_of_file

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

  1. exception Division_by_zero

Exception raised by integer division and remainder operations whentheir second argument is zero.

  1. exception Sys_blocked_io

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

  1. exception Undefined_recursive_module of (string * int * int)

Exception raised when an ill-founded recursive module definitionis evaluated. The arguments are the location of the definition inthe source code (file name, line number, column number).

Comparisons

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

e1 = e2 tests for structural equality of e1 and e2.Mutable structures (e.g. references and arrays) are equalif 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.Left-associative operator, see Ocaml_operators[??] for more information.

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

Negation of (=)[23.3].Left-associative operator, see Ocaml_operators[??] for more information.

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

See (>=)[23.3].Left-associative operator, see Ocaml_operators[??] for more information.

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

See (>=)[23.3].Left-associative operator, see Ocaml_operators[??] for more information.

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

See (>=)[23.3].Left-associative operator, see Ocaml_operators[??] for more information.

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

Structural ordering functions. These functions coincide withthe usual orderings over integers, characters, strings, byte sequencesand floating-point numbers, and extend them to atotal ordering over all types.The ordering is compatible with ( = ). As in the caseof ( = ), mutable structures are compared by contents.Comparison between functional values raises Invalid_argument.Comparison between cyclic structures may not terminate.Left-associative operator, see Ocaml_operators[??] for more information.

  1. 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 integerif x is greater than y. The ordering implemented by compareis compatible with the comparison predicates =, < and >defined above, with one difference on the treatment of the float valuenan[23.3]. Namely, the comparison predicates treat nanas different from any other float value, including itself;while compare treats nan as equal to itself and less than anyother float value. This treatment of nan ensures that comparedefines 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 functionrequired by the Set.Make[??] and Map.Make[??] functors, as well asthe List.sort[??] and Array.sort[??] functions.

  1. val min : 'a -> 'a -> 'a

Return the smaller of the two arguments.The result is unspecified if one of the arguments containsthe float value nan.

  1. val max : 'a -> 'a -> 'a

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

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

e1 == e2 tests for physical equality of e1 and e2.On mutable types such as references, arrays, byte sequences, records withmutable fields and objects with mutable instance variables,e1 == e2 is true if and only if physical modification of e1also affects e2.On non-mutable types, the behavior of ( == ) isimplementation-dependent; however, it is guaranteed thate1 == e2 implies compare e1 e2 = 0.Left-associative operator, see Ocaml_operators[??] for more information.

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

Negation of (==)[23.3].Left-associative operator, see Ocaml_operators[??] for more information.

Boolean operations

  1. val not : bool -> bool

The boolean negation.

  1. 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.Right-associative operator, see Ocaml_operators[??] for more information.

  1. val (&) : bool -> bool -> bool

Deprecated. (&&)[23.3] should be used instead.Right-associative operator, see Ocaml_operators[??] for more information.

  1. 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.Right-associative operator, see Ocaml_operators[??] for more information.

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

Deprecated. (||)[23.3] should be used instead.Right-associative operator, see Ocaml_operators[??] for more information.

Debugging

  1. val __LOC__ : string

LOC returns the location at which this expression appears inthe file currently being parsed by the compiler, with the standarderror format of OCaml: "File %S, line %d, characters %d-%d".

Since: 4.02.0

  1. val __FILE__ : string

FILE returns the name of the file currently beingparsed by the compiler.

Since: 4.02.0

  1. val __LINE__ : int

LINE returns the line number at which this expressionappears in the file currently being parsed by the compiler.

Since: 4.02.0

  1. val __MODULE__ : string

MODULE returns the module name of the file beingparsed by the compiler.

Since: 4.02.0

  1. val __POS__ : string * int * int * int

POS returns a tuple (file,lnum,cnum,enum), correspondingto the location at which this expression appears in the filecurrently being parsed by the compiler. file is the currentfilename, lnum the line number, cnum the character position inthe line and enum the last character position in the line.

Since: 4.02.0

  1. val __LOC_OF__ : 'a -> string * 'a

LOC_OF expr returns a pair (loc, expr) where loc is thelocation of expr in the file currently being parsed by thecompiler, with the standard error format of OCaml: "File %S, line%d, characters %d-%d".

Since: 4.02.0

  1. val __LINE_OF__ : 'a -> int * 'a

LINE_OF expr returns a pair (line, expr), where line is theline number at which the expression expr appears in the filecurrently being parsed by the compiler.

Since: 4.02.0

  1. val __POS_OF__ : 'a -> (string * int * int * int) * 'a

POS_OF expr returns a pair (loc,expr), where loc is atuple (file,lnum,cnum,enum) corresponding to the location atwhich the expression expr appears in the file currently beingparsed by the compiler. file is the current filename, lnum theline number, cnum the character position in the line and enumthe last character position in the line.

Since: 4.02.0

Composition operators

  1. val (|>) : 'a -> ('a -> 'b) -> 'b

Reverse-application operator: x |> f |> g is exactly equivalentto g (f (x)).Left-associative operator, see Ocaml_operators[??] for more information.

Since: 4.01

  1. val (@@) : ('a -> 'b) -> 'a -> 'b

Application operator: g @@ f @@ x is exactly equivalent tog (f (x)).Right-associative operator, see Ocaml_operators[??] for more information.

Since: 4.01

Integer arithmetic

Integers are Sys.int_size bits wide.All operations are taken modulo 2Sys.int_size.They do not fail on overflow.

  1. val (~-) : int -> int

Unary negation. You can also write - e instead of ~- e.Unary operator, see Ocaml_operators[??] for more information.

  1. val (~+) : int -> int

Unary addition. You can also write + e instead of ~+ e.Unary operator, see Ocaml_operators[??] for more information.

Since: 3.12.0

  1. val succ : int -> int

succ x is x + 1.

  1. val pred : int -> int

pred x is x - 1.

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

Integer addition.Left-associative operator, see Ocaml_operators[??] for more information.

  1. val (-) : int -> int -> int

Integer subtraction.Left-associative operator, , see Ocaml_operators[??] for more information.

  1. val ( * ) : int -> int -> int

Integer multiplication.Left-associative operator, see Ocaml_operators[??] for more information.

  1. 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 integerless than or equal to the real quotient of x by y. Moreover,(- x) / y = x / (- y) = - (x / y).Left-associative operator, see Ocaml_operators[??] for more information.

  1. val (mod) : int -> int -> int

Integer remainder. If y is not zero, the resultof x mod y satisfies the following properties:x = (x / y) * y + x mod y andabs(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.Left-associative operator, see Ocaml_operators[??] for more information.

  1. val abs : int -> int

Return the absolute value of the argument. Note that this may benegative if the argument is min_int.

  1. val max_int : int

The greatest representable integer.

  1. val min_int : int

The smallest representable integer.

Bitwise operations

  1. val (land) : int -> int -> int

Bitwise logical and.Left-associative operator, see Ocaml_operators[??] for more information.

  1. val (lor) : int -> int -> int

Bitwise logical or.Left-associative operator, see Ocaml_operators[??] for more information.

  1. val (lxor) : int -> int -> int

Bitwise logical exclusive or.Left-associative operator, see Ocaml_operators[??] for more information.

  1. val lnot : int -> int

Bitwise logical negation.

  1. 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 > Sys.int_size.Right-associative operator, see Ocaml_operators[??] for more information.

  1. 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 ofthe sign of n.The result is unspecified if m < 0 or m > Sys.int_size.Right-associative operator, see Ocaml_operators[??] for more information.

  1. 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 > Sys.int_size.Right-associative operator, see Ocaml_operators[??] for more information.

Floating-point arithmetic

OCaml’s floating-point numbers follow theIEEE 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 numbersare 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 throughfloating-point computations as expected: for instance,1.0 /. infinity is 0.0, and any arithmetic operation with nanas argument returns nan as result.

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

Unary negation. You can also write -. e instead of ~-. e.Unary operator, see Ocaml_operators[??] for more information.

  1. val (~+.) : float -> float

Unary addition. You can also write +. e instead of ~+. e.Unary operator, see Ocaml_operators[??] for more information.

Since: 3.12.0

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

Floating-point addition.Left-associative operator, see Ocaml_operators[??] for more information.

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

Floating-point subtraction.Left-associative operator, see Ocaml_operators[??] for more information.

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

Floating-point multiplication.Left-associative operator, see Ocaml_operators[??] for more information.

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

Floating-point division.Left-associative operator, see Ocaml_operators[??] for more information.

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

Exponentiation.Right-associative operator, see Ocaml_operators[??] for more information.

  1. val sqrt : float -> float

Square root.

  1. val exp : float -> float

Exponential.

  1. val log : float -> float

Natural logarithm.

  1. val log10 : float -> float

Base 10 logarithm.

  1. val expm1 : float -> float

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

Since: 3.12.0

  1. 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

  1. val cos : float -> float

Cosine. Argument is in radians.

  1. val sin : float -> float

Sine. Argument is in radians.

  1. val tan : float -> float

Tangent. Argument is in radians.

  1. 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.

  1. 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.

  1. val atan : float -> float

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

  1. val atan2 : float -> float -> float

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

  1. val hypot : float -> float -> float

hypot x y returns sqrt(x . x + y . y), that is, the lengthof the hypotenuse of a right-angled triangle with sides of lengthx and y, or, equivalently, the distance of the point (x,y)to origin. If one of x or y is infinite, returns infinityeven if the other is nan.

Since: 4.00.0

  1. val cosh : float -> float

Hyperbolic cosine. Argument is in radians.

  1. val sinh : float -> float

Hyperbolic sine. Argument is in radians.

  1. val tanh : float -> float

Hyperbolic tangent. Argument is in radians.

  1. 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.

  1. val floor : float -> float

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

  1. val abs_float : float -> float

abs_float f returns the absolute value of f.

  1. val copysign : float -> float -> float

copysign x y returns a float whose absolute value is that of xand whose sign is that of y. If x is nan, returns nan.If y is nan, returns either x or -. x, but it is notspecified which.

Since: 4.00.0

  1. val mod_float : float -> float -> float

mod_float a b returns the remainder of a with respect tob. The returned value is a -. n *. b, where nis the quotient a /. b rounded towards zero to an integer.

  1. val frexp : float -> float * int

frexp f returns the pair of the significantand the exponent of f. When f is zero, thesignificant x and the exponent n of f are equal tozero. When f is non-zero, they are defined byf = x . 2 * n and 0.5 <= x < 1.0.

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

ldexp x n returns x . 2 * n.

  1. val modf : float -> float * float

modf f returns the pair of the fractional and integralpart of f.

  1. val float : int -> float

Same as float_of_int[23.3].

  1. val float_of_int : int -> float

Convert an integer to floating-point.

  1. val truncate : float -> int

Same as int_of_float[23.3].

  1. 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 therange of representable integers.

  1. val infinity : float

Positive infinity.

  1. val neg_infinity : float

Negative infinity.

  1. val nan : float

A special floating-point value denoting the result of anundefined operation such as 0.0 /. 0.0. Stands for’not a number’. Any floating-point operation with nan asargument returns nan as result. As for floating-point comparisons,=, <, <=, > and >= return false and <> returns trueif one or both of their arguments is nan.

  1. val max_float : float

The largest positive finite value of type float.

  1. val min_float : float

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

  1. val epsilon_float : float

The difference between 1.0 and the smallest exactly representablefloating-point number greater than 1.0.

  1. type fpclass =
  2.   | FP_normal
Normal number, none of the below
  1.   | FP_subnormal
Number very close to 0.0, has reduced precision
  1.   | FP_zero
Number is 0.0 or -0.0
  1.   | FP_infinite
Number is positive or negative infinity
  1.   | FP_nan
Not a number: result of an undefined operation

The five classes of floating-point numbers, as determined bythe classify_float[23.3] function.

  1. 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[??].

  1. val (^) : string -> string -> string

String concatenation.Right-associative operator, see Ocaml_operators[??] for more information.

Character operations

More character operations are provided in module Char[??].

  1. val int_of_char : char -> int

Return the ASCII code of the argument.

  1. val char_of_int : int -> char

Return the character with the given ASCII code.Raise Invalid_argument "char_of_int" if the argument isoutside the range 0–255.

Unit operations

  1. val ignore : 'a -> unit

Discard the value of its argument and return ().For instance, ignore(f x) discards the result ofthe side-effecting function f. It is equivalent tof x; (), except that the latter may generate acompiler warning; writing ignore(f x) insteadavoids the warning.

String conversion functions

  1. val string_of_bool : bool -> string

Return the string representation of a boolean. As the returned valuesmay be shared, the user should not modify them directly.

  1. val bool_of_string_opt : string -> bool option

Convert the given string to a boolean.

Return None if the string is not "true" or "false".

Since: 4.05

  1. val bool_of_string : string -> bool

Same as bool_of_string_opt[23.3], but raiseInvalid_argument "bool_of_string" instead of returning None.

  1. val string_of_int : int -> string

Return the string representation of an integer, in decimal.

  1. val int_of_string_opt : string -> int option

Convert the given string to an integer.The string is read in decimal (by default, or if the stringbegins with 0u), in hexadecimal (if it begins with 0x or0X), in octal (if it begins with 0o or 0O), or in binary(if it begins with 0b or 0B).

The 0u prefix reads the input as an unsigned integer in the range[0, 2*maxint+1]. If the input exceeds max_int[23.3]it is converted to the signed integermin_int + input - max_int - 1.

The (underscore) character can appear anywhere in the stringand is ignored.

Return None if the given string is not a valid representation of aninteger, or if the integer represented exceeds the range of integersrepresentable in type int.

Since: 4.05

  1. val int_of_string : string -> int

Same as int_of_string_opt[23.3], but raiseFailure "int_of_string" instead of returning None.

  1. val string_of_float : float -> string

Return the string representation of a floating-point number.

  1. val float_of_string_opt : string -> float option

Convert the given string to a float. The string is read in decimal(by default) or in hexadecimal (marked by 0x or 0X).

The format of decimal floating-point numbers is [-] dd.ddd (e|E) [+|-] dd , where d stands for a decimal digit.

The format of hexadecimal floating-point numbers is [-] 0(x|X) hh.hhh (p|P) [+|-] dd , where h stands for anhexadecimal digit and d for a decimal digit.

In both cases, at least one of the integer and fractional parts must begiven; the exponent part is optional.

The _ (underscore) character can appear anywhere in the stringand is ignored.

Depending on the execution platforms, other representations offloating-point numbers can be accepted, but should not be relied upon.

Return None if the given string is not a valid representation of a float.

Since: 4.05

  1. val float_of_string : string -> float

Same as float_of_string_opt[23.3], but raiseFailure "float_of_string" instead of returning None.

Pair operations

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

Return the first component of a pair.

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

Return the second component of a pair.

List operations

More list operations are provided in module List[??].

  1. val (@) : 'a list -> 'a list -> 'a list

List concatenation. Not tail-recursive (length of the first argument).Right-associative operator, see Ocaml_operators[??] for more information.

Input/output

Note: all input/output functions can raise Sys_error when the systemcalls they invoke fail.

  1. type in_channel

The type of input channel.

  1. type out_channel

The type of output channel.

  1. val stdin : in_channel

The standard input for the process.

  1. val stdout : out_channel

The standard output for the process.

  1. val stderr : out_channel

The standard error output for the process.

Output functions on standard output

  1. val print_char : char -> unit

Print a character on standard output.

  1. val print_string : string -> unit

Print a string on standard output.

  1. val print_bytes : bytes -> unit

Print a byte sequence on standard output.

Since: 4.02.0

  1. val print_int : int -> unit

Print an integer, in decimal, on standard output.

  1. val print_float : float -> unit

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

  1. val print_endline : string -> unit

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

  1. val print_newline : unit -> unit

Print a newline character on standard output, and flushstandard output. This can be used to simulate linebuffering of standard output.

Output functions on standard error

  1. val prerr_char : char -> unit

Print a character on standard error.

  1. val prerr_string : string -> unit

Print a string on standard error.

  1. val prerr_bytes : bytes -> unit

Print a byte sequence on standard error.

Since: 4.02.0

  1. val prerr_int : int -> unit

Print an integer, in decimal, on standard error.

  1. val prerr_float : float -> unit

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

  1. val prerr_endline : string -> unit

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

  1. val prerr_newline : unit -> unit

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

Input functions on standard input

  1. val read_line : unit -> string

Flush standard output, then read characters from standard inputuntil a newline character is encountered. Return the string ofall characters read, without the newline character at the end.

  1. val read_int_opt : unit -> int option

Flush standard output, then read one line from standard inputand convert it to an integer.

Return None if the line read is not a valid representation of an integer.

Since: 4.05

  1. val read_int : unit -> int

Same as read_int_opt[23.3], but raise Failure "int_of_string"instead of returning None.

  1. val read_float_opt : unit -> float option

Flush standard output, then read one line from standard inputand convert it to a floating-point number.

Return None if the line read is not a valid representation of afloating-point number.

Since: 4.05.0

  1. val read_float : unit -> float

Same as read_float_opt[23.3], but raise Failure "float_of_string"instead of returning None.

General output functions

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

Opening modes for open_out_gen[23.3] andopen_in_gen[23.3].

  1. val open_out : string -> out_channel

Open the named file for writing, and return a new output channelon that file, positioned at the beginning of the file. Thefile is truncated to zero length if it already exists. Itis created if it does not already exists.

  1. val open_out_bin : string -> out_channel

Same as open_out[23.3], but the file is opened in binary mode,so that no translation takes place during writes. On operatingsystems that do not distinguish between text mode and binarymode, this function behaves like open_out[23.3].

  1. 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 modespecifies the opening mode. The extra argument perm specifiesthe file permissions, in case the file must be created.open_out[23.3] and open_out_bin[23.3] are specialcases of this function.

  1. 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 standardoutput and standard error at the right time.

  1. val flush_all : unit -> unit

Flush all open output channels; ignore errors.

  1. val output_char : out_channel -> char -> unit

Write the character on the given output channel.

  1. val output_string : out_channel -> string -> unit

Write the string on the given output channel.

  1. val output_bytes : out_channel -> bytes -> unit

Write the byte sequence on the given output channel.

Since: 4.02.0

  1. val output : out_channel -> bytes -> int -> int -> unit

output oc buf pos len writes len characters from byte sequence buf,starting at offset pos, to the given output channel oc.Raise Invalid_argument "output" if pos and len do notdesignate a valid range of buf.

  1. val output_substring : out_channel -> string -> int -> int -> unit

Same as output but take a string as argument instead ofa byte sequence.

Since: 4.02.0

  1. 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 modulo256.

  1. 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 232.The only reliable way to read it back is through theinput_binary_int[23.3] function. The format is compatible acrossall machines for a given version of OCaml.

  1. val output_value : out_channel -> 'a -> unit

Write the representation of a structured value of any typeto a channel. Circularities and sharing inside the valueare detected and preserved. The object can be read back,by the function input_value[23.3]. See the description of moduleMarshal[??] for more information. output_value[23.3] is equivalentto Marshal.to_channel[??] with an empty list of flags.

  1. val seek_out : out_channel -> int -> unit

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

  1. val pos_out : out_channel -> int

Return the current writing position for the given channel. Doesnot work on channels opened with the Open_append flag (returnsunspecified results).

  1. val out_channel_length : out_channel -> int

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

  1. val close_out : out_channel -> unit

Close the given channel, flushing all buffered write operations.Output functions raise a Sys_error exception when they areapplied 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 operatingsystem signals an error when flushing or closing.

  1. val close_out_noerr : out_channel -> unit

Same as close_out, but ignore all errors.

  1. val set_binary_mode_out : out_channel -> bool -> unit

set_binary_mode_out oc true sets the channel oc to binarymode: no translations take place during output.set_binary_mode_out oc false sets the channel oc to textmode: depending on the operating system, some translationsmay 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 thatdo not distinguish between text mode and binary mode.

General input functions

  1. val open_in : string -> in_channel

Open the named file for reading, and return a new input channelon that file, positioned at the beginning of the file.

  1. val open_in_bin : string -> in_channel

Same as open_in[23.3], but the file is opened in binary mode,so that no translation takes place during reads. On operatingsystems that do not distinguish between text mode and binarymode, this function behaves like open_in[23.3].

  1. 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 argumentsmode and perm specify the opening mode and file permissions.open_in[23.3] and open_in_bin[23.3] are specialcases of this function.

  1. 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.

  1. val input_line : in_channel -> string

Read characters from the given input channel, until anewline character is encountered. Return the string ofall characters read, without the newline character at the end.Raise End_of_file if the end of the file is reachedat the beginning of line.

  1. val input : in_channel -> bytes -> int -> int -> int

input ic buf pos len reads up to len characters fromthe given channel ic, storing them in byte sequence buf, starting atcharacter number pos.It returns the actual number of characters read, between 0 andlen (inclusive).A return value of 0 means that the end of file was reached.A return value between 0 and len exclusive means thatnot all requested len characters were read, either becauseno more characters were available at that time, or becausethe implementation found it convenient to do a partial read;input must be called again to read the remaining characters,if desired. (See also really_input[23.3] for readingexactly len characters.)Exception Invalid_argument "input" is raised if pos and lendo not designate a valid range of buf.

  1. val really_input : in_channel -> bytes -> int -> int -> unit

really_input ic buf pos len reads len characters from channel ic,storing them in byte sequence buf, starting at character number pos.Raise End_of_file if the end of file is reached before lencharacters have been read.Raise Invalid_argument "really_input" ifpos and len do not designate a valid range of buf.

  1. val really_input_string : in_channel -> int -> string

really_input_string ic len reads len characters from channel icand returns them in a new string.Raise End_of_file if the end of file is reached before lencharacters have been read.

Since: 4.02.0

  1. val input_byte : in_channel -> int

Same as input_char[23.3], but return the 8-bit integer representingthe character.Raise End_of_file if an end of file was reached.

  1. val input_binary_int : in_channel -> int

Read an integer encoded in binary format (4 bytes, big-endian)from the given input channel. See output_binary_int[23.3].Raise End_of_file if an end of file was reached while reading theinteger.

  1. val input_value : in_channel -> 'a

Read the representation of a structured value, as producedby output_value[23.3], 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.

  1. val seek_in : in_channel -> int -> unit

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

  1. val pos_in : in_channel -> int

Return the current reading position for the given channel.

  1. val in_channel_length : in_channel -> int

Return the size (number of characters) of the regular fileon which the given channel is opened. If the channel is openedon a file that is not a regular file, the result is meaningless.The returned size does not take into account the end-of-linetranslations that can be performed when reading from a channelopened in text mode.

  1. val close_in : in_channel -> unit

Close the given channel. Input functions raise a Sys_errorexception when they are applied to a closed input channel,except close_in, which does nothing when applied to an alreadyclosed channel.

  1. val close_in_noerr : in_channel -> unit

Same as close_in, but ignore all errors.

  1. val set_binary_mode_in : in_channel -> bool -> unit

set_binary_mode_in ic true sets the channel ic to binarymode: no translations take place during input.set_binary_mode_out ic false sets the channel ic to textmode: depending on the operating system, some translationsmay 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 thatdo not distinguish between text mode and binary mode.

Operations on large files

  1. module LargeFile :

sig

  1. val seek_out : out_channel -> int64 -> unit
  1. val pos_out : out_channel -> int64
  1. val out_channel_length : out_channel -> int64
  1. val seek_in : in_channel -> int64 -> unit
  1. val pos_in : in_channel -> int64
  1. val in_channel_length : in_channel -> int64

end

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

References

  1. type 'a ref = 
  2. {  mutable contents : 'a ;
  3. }

The type of references (mutable indirection cells) containinga value of type 'a.

  1. val ref : 'a -> 'a ref

Return a fresh reference containing the given value.

  1. val (!) : 'a ref -> 'a

!r returns the current contents of reference r.Equivalent to fun r -> r.contents.Unary operator, see Ocaml_operators[??] for more information.

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

r := a stores the value of a in reference r.Equivalent to fun r v -> r.contents <- v.Right-associative operator, see Ocaml_operators[??] for more information.

  1. val incr : int ref -> unit

Increment the integer contained in the given reference.Equivalent to fun r -> r := succ !r.

  1. val decr : int ref -> unit

Decrement the integer contained in the given reference.Equivalent to fun r -> r := pred !r.

Result type

  1. type ('a, 'b) result =
  2.   | Ok of 'a
  3.   | Error of 'b

Since: 4.03.0

Operations on format strings

Format strings are character strings with special lexical conventionsthat defines the functionality of formatted input/output functions. Formatstrings are used to read data with formatted input functions from moduleScanf[??] and to print data with formatted output functions from modulesPrintf[??] and Format[??].

Format strings are made of three kinds of entities:

  • conversions specifications, introduced by the special character '%'followed by one or more characters specifying what kind of argument toread or print,
  • formatting indications, introduced by the special character '@'followed by one or more characters specifying how to read or print theargument,
  • plain characters that are regular characters with usual lexicalconventions. Plain characters specify string literals to be read in theinput or printed in the output.There is an additional lexical rule to escape the special characters '%'and '@' in format strings: if a special character follows a '%'character, it is treated as a plain character. In other words, "%%" isconsidered as a plain '%' and "%@" as a plain '@'.

For more information about conversion specifications and formattingindications available, read the documentation of modules Scanf[??],Printf[??] and Format[??].

Format strings have a general and highly polymorphic type('a, 'b, 'c, 'd, 'e, 'f) format6.The two simplified types, format and format4 below areincluded for backward compatibility with earlier releases ofOCaml.

The meaning of format string type parameters is as follows:

  • 'a is the type of the parameters of the format for formatted outputfunctions (printf-style functions);'a is the type of the values read by the format for formatted inputfunctions (scanf-style functions).

  • 'b is the type of input source for formatted input functions and thetype of output target for formatted output functions.For printf-style functions from module Printf[??], 'b is typicallyout_channel;for printf-style functions from module Format[??], 'b is typicallyFormat.formatter[??];for scanf-style functions from module Scanf[??], 'b is typicallyScanf.Scanning.in_channel[??].Type argument 'b is also the type of the first argument given touser’s defined printing functions for %a and %t conversions,and user’s defined reading functions for %r conversion.

  • 'c is the type of the result of the %a and %t printingfunctions, and also the type of the argument transmitted to thefirst argument of kprintf-style functions or to thekscanf-style functions.

  • 'd is the type of parameters for the scanf-style functions.
  • 'e is the type of the receiver function for the scanf-style functions.
  • 'f is the final result type of a formatted input/output functioninvocation: for the printf-style functions, it is typically unit;for the scanf-style functions, it is typically the result type of thereceiver function.
  1. type ('a, 'b, 'c, 'd, 'e, 'f) format6 = ('a, 'b, 'c, 'd, 'e, 'f) CamlinternalFormatBasics.format6 

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

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

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

Converts a format string into a string.

  1. val format_of_string :
  2.   ('a, 'b, 'c, 'd, 'e, 'f) format6 ->
  3.   ('a, 'b, 'c, 'd, 'e, 'f) format6

format_of_string s returns a format string read from the stringliteral s.Note: format_of_string can not convert a string argument that is not aliteral. If you need this functionality, use the more generalScanf.format_from_string[??] function.

  1. val (^^) :
  2.   ('a, 'b, 'c, 'd, 'e, 'f) format6 ->
  3.   ('f, 'b, 'c, 'e, 'g, 'h) format6 ->
  4.   ('a, 'b, 'c, 'd, 'g, 'h) format6

f1 ^^ f2 catenates format strings f1 and f2. The result is aformat string that behaves as the concatenation of format strings f1 andf2: in case of formatted output, it accepts arguments from f1, thenarguments from f2; in case of formatted input, it returns results fromf1, then results from f2.Right-associative operator, see Ocaml_operators[??] for more information.

Program termination

  1. val exit : int -> 'a

Terminate the process, returning the given status codeto 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 programterminates normally. An implicit exit 2 is performed if the programterminates early because of an uncaught exception.

  1. val at_exit : (unit -> unit) -> unit

Register the given function to be called at program terminationtime. The functions registered with at_exit will be called whenthe program does any of the following:
  • executes exit[23.3]
  • terminates, either normally or because of an uncaughtexception
  • executes the C function caml_shutdown.The functions are called in ’last in, first out’ order: thefunction most recently added with at_exit is called first.

Standard library modules

  1. module Arg :

Arg

  1. module Array :

Array

  1. module ArrayLabels :

ArrayLabels

  1. module Bigarray :

Bigarray

  1. module Bool :

Bool

  1. module Buffer :

Buffer

  1. module Bytes :

Bytes

  1. module BytesLabels :

BytesLabels

  1. module Callback :

Callback

  1. module Char :

Char

  1. module Complex :

Complex

  1. module Digest :

Digest

  1. module Ephemeron :

Ephemeron

  1. module Filename :

Filename

  1. module Float :

Float

  1. module Format :

Format

  1. module Fun :

Fun

  1. module Gc :

Gc

  1. module Genlex :

Genlex

  1. module Hashtbl :

Hashtbl

  1. module Int :

Int

  1. module Int32 :

Int32

  1. module Int64 :

Int64

  1. module Lazy :

Lazy

  1. module Lexing :

Lexing

  1. module List :

List

  1. module ListLabels :

ListLabels

  1. module Map :

Map

  1. module Marshal :

Marshal

  1. module MoreLabels :

MoreLabels

  1. module Nativeint :

Nativeint

  1. module Obj :

Obj

  1. module Oo :

Oo

  1. module Option :

Option

  1. module Parsing :

Parsing

  1. module Pervasives :

Pervasives

  1. module Printexc :

Printexc

  1. module Printf :

Printf

  1. module Queue :

Queue

  1. module Random :

Random

  1. module Result :

Result

  1. module Scanf :

Scanf

  1. module Seq :

Seq

  1. module Set :

Set

  1. module Spacetime :

Spacetime

  1. module Stack :

Stack

  1. module StdLabels :

StdLabels

  1. module Stream :

Stream

  1. module String :

String

  1. module StringLabels :

StringLabels

  1. module Sys :

Sys

  1. module Uchar :

Uchar

  1. module Weak :

Weak