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Module Standard


module Standard: Extlib.ExtPervasives.Pervasives
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 Standard.

Automatically opened module.
Author(s): Xavier Leroy (Base module), Nicolas Cannasse, David Teller, Zheng Li


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.

Note This function is provided as a simple technique for exiting a function or a program with an error message. It is however considered a bad practice to define a library which makes use of this function. So don't use it except for quick experiments and for teaching.


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 Standard.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.

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 does not terminate.
val (<>) : 'a -> 'a -> bool
Negation of Standard.(=).
val (<) : 'a -> 'a -> bool
See Standard.(>=).
val (>) : 'a -> 'a -> bool
See Standard.(>=).
val (<=) : 'a -> 'a -> bool
See Standard.(>=).
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 does 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 Standard.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.
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, physical equality is identical to 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; however, it is guaranteed that e1 == e2 implies compare e1 e2 = 0.
val (!=) : 'a -> 'a -> bool
Negation of Standard.(==).

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.Standard.(&&) 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.

Integer arithmetic

Integers are 31 bits wide (or 63 bits on 64-bit processors). All operations are taken modulo 231 (or 263).

Note These operations do not fail on overflow. In other words, although Standard.max_int is the largest possible integer, addition max_int + 1 will succeed. However, the result if this addition is min_int. If you wish your operations to fail on overflow, open module Data.Numeric.SafeInt.

More operations on integers are defined in Int, SafeInt, Int32, Int64 and Native_int.

val (~-) : int -> int
Unary negation. You can also write -e instead of ~-e.
val succ : int -> int
succ x is x+1.
val pred : int -> int
pred x is x-1.
val (+) : int -> int -> int
Integer addition.
val (-) : int -> int -> int
Integer subtraction.
val (*) : int -> int -> int
Integer multiplication.
val (/) : int -> int -> int
Integer division. Raise Division_by_zero if the second argument is 0. Integer division rounds the real quotient of its arguments towards zero. More precisely, if x >= 0 and y > 0, x / y is the greatest integer less than or equal to the real quotient of x by y. Moreover, (-x) / y = x / (-y) = -(x / y).
val mod : int -> int -> int
Integer remainder. If y is not zero, the result of x mod y satisfies the following properties: x = (x / y) * y + x mod y and abs(x mod y) <= abs(y)-1. If y = 0, x mod y raises Division_by_zero. Notice that x mod y is nonpositive if and 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 operation with nan as argument returns nan as result.

More floating-point operations are defined in Float.

val (~-.) : float -> float
Unary negation. You can also write -.e instead of ~-.e.
val (+.) : float -> float -> float
Floating-point addition
val (-.) : float -> float -> float
Floating-point subtraction
val (*.) : float -> float -> float
Floating-point multiplication
val (/.) : float -> float -> float
Floating-point division.
val (**) : float -> float -> float
Exponentiation
val sqrt : float -> float
Square root
val exp : float -> float
Exponential.
val log : float -> float
Natural logarithm.
val log10 : float -> float
Base 10 logarithm.
val cos : float -> float
See Standard.atan2.
val sin : float -> float
See Standard.atan2.
val tan : float -> float
See Standard.atan2.
val acos : float -> float
See Standard.atan2.
val asin : float -> float
See Standard.atan2.
val atan : float -> float
See Standard.atan2.
val atan2 : float -> float -> float
The usual trigonometric functions.
val cosh : float -> float
See Standard.tanh.
val sinh : float -> float
See Standard.tanh.
val tanh : float -> float
The usual hyperbolic trigonometric functions.
val ceil : float -> float
See Standard.floor.
val floor : float -> float
Round the given float to an integer value. floor f returns the greatest integer value less than or equal to f. ceil f returns the least integer value greater than or equal to f.
val abs_float : float -> float
Return the absolute value of the argument.
val mod_float : float -> float -> float
mod_float a b returns the remainder of a with respect to b. The returned value is a -. n *. b, where n is the quotient a /. b rounded towards zero to an integer.
val frexp : float -> float * int
frexp f returns the pair of the significant and the exponent of f. When f is zero, the significant x and the exponent n of f are equal to zero. When f is non-zero, they are defined by f = x *. 2 ** n and 0.5 <= x < 1.0.
val ldexp : float -> int -> float
ldexp x n returns x *. 2 ** n.
val modf : float -> float * float
modf f returns the pair of the fractional and integral part of f.
val float : int -> float
Same as Standard.float_of_int.
val float_of_int : int -> float
Convert an integer to floating-point.
val truncate : float -> int
Same as Standard.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.

String operations

More string operations are provided in module String.

val (^) : string -> string -> string
String concatenation.
val uppercase : string -> string
Return a copy of the argument, with all lowercase letters translated to uppercase, including accented letters of the ISO Latin-1 (8859-1) character set.
val lowercase : string -> string
Return a copy of the argument, with all uppercase letters translated to lowercase, including accented letters of the ISO Latin-1 (8859-1) character set.

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

More unit operations are provided in module Unit

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

These are the most common string conversion functions. For additional string conversion functions, see in the corresponding module (e.g. for conversion between int32 and string, see module Int32).

val string_of_char : char -> string
creates a string from a char.
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.
val dump : 'a -> string
Attempt to convert a value to a string.

Since types are lost at compile time, the representation might not match your type. For example, None will be printed 0 since they share the same runtime representation.


List operations

More list operations are provided in module List.

val (@) : 'a list -> 'a list -> 'a list
List concatenation.

Input/output

This section only contains the most common input/output operations. More operations may be found in modules IO and File.

val stdin : IO.input
Standard input, as per Unix/Windows conventions (by default, keyboard).

Use this input to read what the user is writing on the keyboard.

val stdout : unit IO.output
Standard output, as per Unix/Windows conventions (by default, console).

Use this output to display regular messages.

val stderr : unit IO.output
Standard error output, as per Unix/Windows conventions.

Use this output to display warnings and error messages.

val stdnull : unit IO.output
An output which discards everything written to it.

Use this output to ignore messages.

val flush_all : unit -> unit
Write all pending data to output channels, ignore all errors.

It is normally not necessary to call this function, as all pending data is written when an output channel is closed or when the program itself terminates, either normally or because of an uncaught exception. However, this function is useful for debugging, as it forces pending data to be written immediately.


Output functions on standard output

val print_bool : bool -> unit
Print a boolean 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.
val print_guess : 'a -> unit
Attempt to print the representation of a runtime value on the standard output. See remarks for Standard.dump. This function is useful mostly for debugging. As a general rule, it should not be used in production code.
val print_all : IO.input -> unit
Print the contents of an input to the standard output.

Output functions on standard error

val prerr_bool : bool -> unit
Print a boolean to stderr.
val prerr_char : char -> unit
Print a character on standard error.
val prerr_string : string -> unit
Print a string on standard error.
val prerr_int : int -> unit
Print an integer, in decimal, on standard error.
val prerr_float : float -> unit
Print a floating-point number, in decimal, on standard error.
val prerr_endline : string -> unit
Print a string, followed by a newline character on standard error and flush standard error.
val prerr_newline : unit -> unit
Print a newline character on standard error, and flush standard error.
val prerr_guess : 'a -> unit
Attempt to print the representation of a runtime value on the error output. See remarks for Standard.dump. This function is useful mostly for debugging.
val prerr_all : IO.input -> unit
Print the contents of an input to the error output.

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

val open_out : ?mode:File.open_out_flag list ->
       ?perm:File.permission -> string -> unit IO.output
Open the named file for writing, and return a new output channel on that file. You will need to close the file once you have finished using it.

You may use optional argument mode to decide whether the output will overwrite the contents of the file (by default) or to add things at the end of the file, whether the file should be created if it does not exist yet (the default) or not, whether this operation should proceed if the file exists already (the default) or not, whether the file should be opened as text (the default) or as binary, and whether the file should be opened for non-blocking operations.

You may use optional argument perm to specify the permissions of the file, as per Unix conventions. By default, files are created with default permissions (which depend on your setup).

Raise Sys_error if the file could not be opened.

val open_out_bin : string -> unit IO.output
Same as Standard.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 Standard.open_out without any mode or perm.
val open_out_gen : open_flag list -> int -> string -> unit IO.output
Deprecated.Use open_out instead
open_out_gen mode perm filename opens the named file for writing, as described above. The extra argument mode specifies the opening mode. The extra argument perm specifies the file permissions, in case the file must be created.
val flush : unit IO.output -> unit
Flush the buffer associated with the given output, performing all pending writes on that channel. Interactive programs must be careful about flushing standard output and standard error at the right time.
val output_char : unit IO.output -> char -> unit
Write the character on the given output channel.
val output_string : unit IO.output -> string -> unit
Write the string on the given output channel.
val output_rope : unit IO.output -> Rope.t -> unit
Write the rope on the given output channel.
val output : unit IO.output -> 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 : unit IO.output -> 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 : unit IO.output -> 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 the Standard.input_binary_int function. The format is compatible across all machines for a given version of Objective Caml.
val output_value : unit IO.output -> '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 Standard.input_value. See the description of module Marshal for more information. Standard.output_value is equivalent to Marshal.output with an empty list of flags.
val close_out : unit IO.output -> 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 : unit IO.output -> unit
Same as close_out, but ignore all errors.

General input functions

val open_in : ?mode:File.open_in_flag list ->
       ?perm:File.permission -> string -> IO.input
Open the named file for reading. You will need to close the file once you have finished using it.

You may use optional argument mode to decide whether the opening should fail if the file doesn't exist yet (by default) or whether the file should be created if it doesn't exist yet, whether the opening should fail if the file already exists or not (by default), whether the file should be read as binary (by default) or as text, and whether reading should be non-blocking.

You may use optional argument perm to specify the permissions of the file, should it be created, as per Unix conventions. By default, files are created with default permissions (which depend on your setup).

Raise Sys_error if the file could not be opened.

val open_in_bin : string -> IO.input
Same as Standard.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 Standard.open_in.
val open_in_gen : open_flag list -> int -> string -> IO.input
Deprecated.Use open_in instead
open_in 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. Standard.open_in and Standard.open_in_bin are special cases of this function.
val input_char : IO.input -> char
Read one character from the given input channel. Raise End_of_file if there are no more characters to read.
val input_line : IO.input -> 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 : IO.input -> 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 Standard.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 : IO.input -> 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 : IO.input -> int
Same as Standard.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 : IO.input -> int
Read an integer encoded in binary format (4 bytes, big-endian) from the given input channel. See Standard.output_binary_int. Raise End_of_file if an end of file was reached while reading the integer.
val input_value : IO.input -> 'a
Read the representation of a structured value, as produced by Standard.output_value, and return the corresponding value. This function is identical to Marshal.input; see the description of module Marshal for more information, in particular concerning the lack of type safety.
val close_in : IO.input -> 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 : IO.input -> unit
Same as close_in, but ignore all errors.

References

More operations on references are defined in module Ref.

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

type ('a, 'b, 'c, 'd) format4 = ('a, 'b, 'c, 'c, 'c, 'd) format6
See modules Printf and Scanf for more operations on format strings.
type ('a, 'b, 'c) format = ('a, 'b, 'c, 'c) format4
Simplified type for format strings, included for backward compatibility with earlier releases of Objective Caml. 'a is the type of the parameters of the format, 'c is the result type for the "printf"-style function, and 'b is the type of the first argument given to %a and %t printing functions.
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.

Fundamental functions and operators

val identity : 'a -> 'a
The identity function.
val undefined : ?message:string -> 'a -> 'b
The undefined function.

Evaluating undefined x always fails and raises an exception "Undefined". Optional argument message permits the customization of the error message.

val (|>) : 'a -> ('a -> 'b) -> 'b
Function application. x |> f is equivalent to f x.

This operator is commonly used to write a function composition by order of evaluation (the order used in object-oriented programming) rather than by inverse order (the order typically used in functional programming).

For instance, g (f x) means "apply f to x, then apply g to the result." The corresponding notation in most object-oriented programming languages would be somewhere along the lines of x.f.g (), or "starting from x, apply f, then apply g." In OCaml, operator ( |> ) this latest notation maps to x |> f |> g, or

This operator may also be useful for composing sequences of function calls without too many parenthesis.

val (**>) : ('a -> 'b) -> 'a -> 'b
Function application. f **> x is equivalent to f x.

This operators may be useful for composing sequences of function calls without too many parenthesis.

Note The name of this operator is not written in stone. It is bound to change soon.

val (|-) : ('a -> 'b) -> ('b -> 'c) -> 'a -> 'c
Function composition. f |- g is fun x -> g (f x). This is also equivalent to applying <** twice.
val (-|) : ('a -> 'b) -> ('c -> 'a) -> 'c -> 'b
Function composition. f -| g is fun x -> f (g x). Mathematically, this is operator o.
val flip : ('a -> 'b -> 'c) -> 'b -> 'a -> 'c
Argument flipping.

flip f x y is f y x. Don't abuse this function, it may shorten considerably your code but it also has the nasty habit of making it harder to read.

val (***) : ('a -> 'b) -> ('c -> 'd) -> 'a * 'c -> 'b * 'd
Function pairing.

f *** g is fun (x,y) -> (f x, g y).

val (&&&) : ('a -> 'b) -> ('a -> 'c) -> 'a -> 'b * 'c
Applying two functions to the same argument.

f &&& g is fun x -> (f x, g x).

val first : ('a -> 'b) -> 'a * 'c -> 'b * 'c
Apply a function to the first element of a pair.

first f (x, y) is (f x, y)

val second : ('a -> 'b) -> 'c * 'a -> 'c * 'b
Apply a function to the second element of a pair.

second f (x, y) is (x, f y)

val curry : ('a * 'b -> 'c) -> 'a -> 'b -> 'c
Convert a function which accepts a pair of arguments into a function which accepts two arguments.

curry f is fun x y -> f (x,y)

val uncurry : ('a -> 'b -> 'c) -> 'a * 'b -> 'c
Convert a function which accepts a two arguments into a function which accepts a pair of arguments.

uncurry f is fun (x, y) -> f x y

val const : 'a -> 'b -> 'a
Ignore its second argument.

const x is the function which always returns x.

val unique : unit -> int
Returns an unique identifier every time it is called.

Note This is thread-safe.

val finally : (unit -> unit) -> ('a -> 'b) -> 'a -> 'b
finally fend f x calls f x and then fend() even if f x raised an exception.
val args : unit -> string Enum.t
An enumeration of the arguments passed to this program through the command line.

args () is given by the elements of Sys.argv, minus the first element.

val exe : string
The name of the current executable.

exe is given by the first argument of Sys.argv


Enumerations

In OCaml Batteries Included, all data structures are enumerable, which means that they support a number of standard operations, transformations, etc. The general manner of enumerating the contents of a data structure is to invoke the enum function of your data structure.

For instance, you may use the Standard.foreach loop to apply a function f to all the consecutive elements of a string s. For this purpose, you may write either foreach (String.enum s) f or open String in foreach (enum s) f. Either possibility states that you are enumerating through a character string s. Should you prefer your enumeration to proceed from the end of the string to the beginning, you may replace String.enum with String.backwards. Therefore, either foreach (String.backwards s) f or open String in foreach (backwards s) f will apply f to all the consecutive elements of string s, from the last to the first.

Similarly, you may use List.enum instead of String.enum to visit the elements of a list in the usual order, or List.backwards instead of String.backwards to visit them in the opposite order, or Hashtbl.enum for hash tables, etc.

More operations on enumerations are defined in module Enum, including the necessary constructors to make your own structures enumerable.

The various kinds of loops are detailed further in this documentation.

val foreach : 'a Enum.t -> ('a -> unit) -> unit
Imperative loop on an enumeration.

foreach e f applies function f to each successive element of e. For instance, foreach (1 -- 10) print_int invokes function print_int on 1, 2, ..., 10, printing 12345678910.

Note This function is one of the many loops available on enumerations. Other commonly used loops are Standard.iter (same usage scenario as foreach, but with different notations), Standard.map (convert an enumeration to another enumeration) or Standard.fold (flatten an enumeration by applying an operation to each element).


General-purpose loops

The following functions are the three main general-purpose loops available in OCaml. By opposition to the loops available in imperative languages, OCaml loops are regular functions, which may be passed, composed, currified, etc. In particular, each of these loops may be considered either as a manner of applying a function to a data structure or as transforming a function into another function which will act on a whole data structure.

For instance, if f is a function operating on one value, you may lift this function to operate on all values of an enumeration (and consequently on all values of any data structure of OCaml Batteries Included) by applying Standard.iter, Standard.map or Standard.fold to this function.

val iter : ('a -> unit) -> 'a Enum.t -> unit
Imperative loop on an enumeration. This loop is typically used to lift a function with an effect but no meaningful result and get it to work on enumerations.

If f is a function iter f is a function which behaves as f but acts upon enumerations rather than individual elements. As indicated in the type of iter, f must produce values of type unit (i.e. f has no meaningful result) the resulting function produces no meaningful result either.

In other words, iter f is a function which, when applied upon an enumeration e, calls f with each element of e in turn.

For instance, iter f (1 -- 10) invokes function f on 1, 2, ..., 10 and produces value ().

val map : ('a -> 'b) -> 'a Enum.t -> 'b Enum.t
Transformation loop on an enumeration, used to build an enumeration from another enumeration. This loop is typically used to transform an enumeration into another enumeration with the same number of elements, in the same order.

If f is a function, map f e is a function which behaves as f but acts upon enumerations rather than individual elements -- and builds a new enumeration from the results of each application.

In other words, map f is a function which, when applied upon an enumeration containing elements e1, e2, ..., produces enumeration f e1, f e2, ...

For instance, if odd is the function which returns true when applied to an odd number or false when applied to an even number, map odd (1 -- 10) produces enumeration true, false, true, ..., false.

Similarly, if square is the function fun x -> x * x, map square (1 -- 10) produces the enumeration of the square numbers of all numbers between 1 and 10.

val reduce : ('a -> 'a -> 'a) -> 'a Enum.t -> 'a
Transformation loop on an enumeration, used to build a single value from an enumeration.

If f is a function and e is an enumeration, reduce f e applies function f to the first two elements of e, then to the result of this expression and to the third element of e, then to the result of this new expression and to the fourth element of e...

In other words, fold f e returns a_1 if e contains only one element, otherwise f (... (f (f a1) a2) ...) aN where a1..N are the elements of e.

val fold : ('a -> 'b -> 'a) -> 'a -> 'b Enum.t -> 'a
Transformation loop on an enumeration, used to build a single value from an enumeration. This is the most powerful general-purpose loop and also the most complex.

If f is a function, fold f v e applies f v to the first element of e, then, calling acc_1 the result of this operation, applies f acc_1 to the second element of e, then, calling acc_2 the result of this operation, applies f acc_2 to the third element of e...

In other words, fold f v e returns v if e is empty, otherwise f (... (f (f v a1) a2) ...) aN where a1..N are the elements of e.

For instance, if add is the function fun x y -> x + y, fold add 0 is the function which computes the sum of the elements of an enumeration. Therefore, fold add 0 (1 -- 10) produces result 55.

val scanl : ('a -> 'b -> 'a) -> 'a -> 'b Enum.t -> 'a Enum.t
Functional loop on an enumeration, used to build an enumeration from both an enumeration and an initial value. This function may be seen as a variant of Standard.fold which returns not only the final result of Standard.fold but the enumeration of all the intermediate results of Standard.fold.

If f is a function, scanl f v e is applies f v to the first element of e, then, calling acc_1 the result of this operation, applies f acc_1 to the second element of e, then, calling acc_2 the result of this operation, applies f acc_2 to the third element of e...

For instance, if add is the function fun x y -> x + y, scanl add 0 is the function which computes the sum of the elements of an enumeration. Therefore, scanl add 0 (1 -- 10) produces result the enumeration with elements 0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55.

val (/@) : 'a Enum.t -> ('a -> 'b) -> 'b Enum.t
val (@/) : ('a -> 'b) -> 'a Enum.t -> 'b Enum.t
Mapping operators.

These operators have the same meaning as function Standard.map but are sometimes more readable than this function, when chaining several transformations in a row.


Other operations on enumerations

val exists : ('a -> bool) -> 'a Enum.t -> bool
exists f e returns true if there is some x in e such that f x
val for_all : ('a -> bool) -> 'a Enum.t -> bool
exists f e returns true if for every x in e, f x is true
val find : ('a -> bool) -> 'a Enum.t -> 'a
find f e returns the first element x of e such that f x returns true, consuming the enumeration up to and including the found element, or, raises Not_found if no such element exists in the enumeration, consuming the whole enumeration in the search.

Since find consumes a prefix of the enumeration, it can be used several times on the same enumeration to find the next element.

val peek : 'a Enum.t -> 'a option
peek e returns None if e is empty or Some x where x is the next element of e. The element is not removed from the enumeration.
val get : 'a Enum.t -> 'a option
get e returns None if e is empty or Some x where x is the next element of e, in which case the element is removed from the enumeration.
val push : 'a Enum.t -> 'a -> unit
push e x will add x at the beginning of e.
val junk : 'a Enum.t -> unit
junk e removes the first element from the enumeration, if any.
val filter : ('a -> bool) -> 'a Enum.t -> 'a Enum.t
filter f e returns an enumeration over all elements x of e such as f x returns true.
val (//) : 'a Enum.t -> ('a -> bool) -> 'a Enum.t
Filtering (pronounce this operator name "such that").

For instance, (1 -- 37) // odd is the enumeration of all odd numbers between 1 and 37.

val concat : 'a Enum.t Enum.t -> 'a Enum.t
concat e returns an enumeration over all elements of all enumerations of e.
val (--) : int -> int -> int Enum.t
Enumerate numbers.

5 -- 10 is the enumeration 5,6,7,8,9,10. 10 -- 5 is the empty enumeration

val (--.) : float * float -> float -> float Enum.t
(a, step) --. b) creates a float enumeration from a to b with an increment of step between elements.

(5.0, 1.0) --. 10.0 is the enumeration 5.0,6.0,7.0,8.0,9.0,10.0. (10.0, -1.0) --. 5.0 is the enumeration 10.0,9.0,8.0,7.0,6.0,5.0. (10.0, 1.0) --. 1.0 is the empty enumeration.

val (---) : int -> int -> int Enum.t
As --, but accepts enumerations in reverse order.

5 --- 10 is the enumeration 5,6,7,8,9,10. 10 --- 5 is the enumeration 10,9,8,7,6,5.

val (--~) : char -> char -> char Enum.t
As ( -- ), but for characters.
val print : ?first:string ->
       ?last:string ->
       ?sep:string ->
       ('a Extlib.InnerIO.output -> 'b -> unit) ->
       'a Extlib.InnerIO.output -> 'b Enum.t -> unit
Print and consume the contents of an enumeration.

Results

type ('a, 'b) result = ('a, 'b) Extlib.Std.result =
| Ok of 'a
| Bad of 'b 
val sexp_of_result : ('a -> Sexplib.Sexp.t) ->
       ('b -> Sexplib.Sexp.t) ->
       ('a, 'b) result -> Sexplib.Sexp.t
val result_of_sexp : (Sexplib.Sexp.t -> 'a) ->
       (Sexplib.Sexp.t -> 'b) ->
       Sexplib.Sexp.t -> ('a, 'b) result

Thread-safety internals

Unless you are attempting to adapt Batteries Included to a new model of concurrency, you probably won't need this.

val lock : Concurrency.lock ref
A lock used to synchronize internal operations.

By default, this is Concurrency.nolock. However, if you're using a version of Batteries compiled in threaded mode, this uses Threads.Mutex. If you're attempting to use Batteries with another concurrency model, set the lock appropriately.