Stdlib(3)

📦
version 5.5.0 · 19 versions
, in arch rolling

🌈 NAME 🌈

okay so bestie, this is Stdlib(3) from the OCaml library, and the name line is literally:

Stdlib - The OCaml Standard library.

🎀 Module 🎀

Module Stdlib — and the signature is this exact lil thing:

Module Stdlib
 : sig end

✨ Documentation ✨

The OCaml Standard library. No cap, that's the whole vibe.

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 Stdlib. So you can just say the thing, you don't gotta do the whole government-name situation every time 💅.

In particular, it provides the basic operations over the built-in types (numbers, booleans, byte sequences, strings, exceptions, references, lists, arrays, input-output channels, ...) and the modules . Yes, literally "and the modules ." — that trailing dot is doing its best, okay 🫶.

💀 Exceptions 💀

  • val raise : exn -> 'a — raises the exception value you hand it. iconic behavior, honestly 🔥.
  • val raise_notrace : exn -> 'a — a faster version of raise which does not record the backtrace. Since 4.02.
  • val invalid_arg : string -> 'a — raises exception Invalid_argument with the given string.
  • val failwith : string -> 'a — raises exception Failure with the given string.
  • exception Exit — the Exit exception is not raised by any library function. It is provided for use in your programs. it's giving "built-in, but make it your problem" 💀.
  • 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 match keyword in the source code (file name, line number, column number). very "where did the vibes go wrong" energy 🔍.
  • exception Assert_failure of (string * int * int) — exception raised when an assertion fails. The arguments are the location of the assert keyword in the source code (file name, line number, column number).
  • exception Invalid_argument of string — exception raised by library functions to signal that the given arguments do not make sense. The string gives some information to the programmer. As a general rule, this exception should not be caught, it denotes a programming error and the code should be modified not to trigger it. periodt 🚨.
  • exception Failure of string — exception raised by library functions to signal that they are undefined on the given arguments. The string is meant to give some information to the programmer; you must not pattern match on the string literal because it may change in future versions (use Failure _ instead). iykyk.
  • exception Not_found — exception raised by search functions when the desired object could not be found. literally the "bestie where are you" of exceptions 😭.
  • exception Out_of_memory — exception raised by the garbage collector when there is insufficient memory to complete the computation. (Not reliable for allocations on the minor heap.) that parenthetical is important, don't skip it bestie 🧠.
  • 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. Before 4.10, it was not fully implemented by the native-code compiler. ancient lore 💀.
  • exception Sys_error of string — exception raised by the input/output functions to report an operating system error. The string is meant to give some information to the programmer; you must not pattern match on the string literal because it may change in future versions (use Sys_error _ instead). same rule, different exception, we stay consistent 💅.
  • exception End_of_file — exception raised by input functions to signal that the end of file has been reached. the "that's all folks" of input 🎬.
  • exception Division_by_zero — exception raised by integer division and remainder operations when their second argument is zero. math said absolutely not 🙈.
  • 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 Undefined_recursive_module of (string * int * int) — exception raised when an ill-founded recursive module definition is evaluated. The arguments are the location of the definition in the source code (file name, line number, column number). recursive modules said "trust me" and then did not trust themselves 😭.

⚖️ Comparisons ⚖️

  • val (=) : 'a -> 'a -> bool — alias of Repr.equal. Left-associative operator, see Ocaml_operators for more information.
  • val (<>) : 'a -> 'a -> bool — negation of Repr.equal. Left-associative operator, see Ocaml_operators for more information.
  • val (<) : 'a -> 'a -> bool — see (>=). Left-associative operator, see Ocaml_operators for more information.
  • val (>) : 'a -> 'a -> bool — see (>=). Left-associative operator, see Ocaml_operators for more information.
  • val (<=) : 'a -> 'a -> bool — see (>=). Left-associative operator, see Ocaml_operators for more information.
  • val (>=) : 'a -> 'a -> bool — structural ordering functions. These functions coincide with the usual orderings over integers, characters, strings, byte sequences and floating-point numbers, and extend them to a total ordering over all types. The ordering is compatible with Repr.equal. As in the case of Repr.equal, 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. highkey a lot, but every word matters 💖.
  • val compare : 'a -> 'a -> int — alias of Repr.compare.
  • val min : 'a -> 'a -> 'a — alias of Repr.min.
  • val max : 'a -> 'a -> 'a — alias of Repr.max.
  • val (==) : 'a -> 'a -> bool — alias of Repr.phys_equal. Left-associative operator, see Ocaml_operators for more information.
  • val (!=) : 'a -> 'a -> bool — negation of Repr.phys_equal. Left-associative operator, see Ocaml_operators for more information.

🔘 Boolean operations 🔘

  • val not : bool -> bool — the boolean negation. the classic flip ✨.
  • 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. short-circuit queen 👑.
  • 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. also short-circuit royalty 💅.

🐞 Debugging 🐞

  • val __LOC__ : string — __LOC__ returns the location at which this expression appears in the file currently being parsed by the compiler, with the standard error format of OCaml: "File %S, line %d, characters %d-%d". Since 4.02. lil built-in snitch, but make it helpful 🕵️.
  • val __FILE__ : string — __FILE__ returns the name of the file currently being parsed by the compiler. Since 4.02.
  • val __LINE__ : int — __LINE__ returns the line number at which this expression appears in the file currently being parsed by the compiler. Since 4.02.
  • val __MODULE__ : string — __MODULE__ returns the module name of the file being parsed by the compiler. Since 4.02.
  • val __POS__ : string * int * int * int — __POS__ returns a tuple (file,lnum,cnum,enum), corresponding to the location at which this expression appears in the file currently being parsed by the compiler. file is the current filename, lnum the line number, cnum the character position in the line and enum the last character position in the line. Since 4.02. all the coordinates, bestie 📍.
  • val __FUNCTION__ : string — __FUNCTION__ returns a string of the form "N0n1n2..." where N0 is the name of the current compilation unit and the ni are the names of the successive scopes leading to the location of the call. Each of the scopes has one of the following forms:
    • .n if n is the name of a function, module, class or value definition, or
    • #n if n is the name of a method, or
    • .(fun) if the scope corresponds to an anonymous function.

Note that the precise format may change in the future. Since 4.12. it's giving ancestry.com for functions 🌳.

  • val __LOC_OF__ : 'a -> string * 'a — __LOC_OF__ expr returns a pair (loc, expr) where loc is the location of expr in the file currently being parsed by the compiler, with the standard error format of OCaml: "File %S, line %d, characters %d-%d". Since 4.02.
  • val __LINE_OF__ : 'a -> int * 'a — __LINE_OF__ expr returns a pair (line, expr), where line is the line number at which the expression expr appears in the file currently being parsed by the compiler. Since 4.02.
  • val __POS_OF__ : 'a -> (string * int * int * int) * 'a — __POS_OF__ expr returns a pair (loc,expr), where loc is a tuple (file,lnum,cnum,enum) corresponding to the location at which the expression expr appears in the file currently being parsed by the compiler. file is the current filename, lnum the line number, cnum the character position in the line and enum the last character position in the line. Since 4.02.

🧩 Composition operators 🧩

  • val (|>) : 'a -> ('a -> 'b) -> 'b — reverse-application operator: x |> f |> g is exactly equivalent to g (f (x)). Left-associative operator, see Ocaml_operators for more information. Since 4.01. pipeline bestie, we love a clean flow 🌊.
  • val (@@) : ('a -> 'b) -> 'a -> 'b — application operator: g @@ f @@ x is exactly equivalent to g (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 2^ Sys.int_size. They do not fail on overflow. no overflow drama, just wrap-around ✨.

  • val (~-) : int -> int — unary negation. You can also write - e instead of ~- e. Unary operator, see Ocaml_operators for more information.
  • val (~+) : int -> int — unary addition. You can also write + e instead of ~+ e. Unary operator, see Ocaml_operators for more information. Since 3.12.
  • val succ : int -> int — succ x is x + 1.
  • val pred : int -> int — pred x is x - 1.
  • val (+) : int -> int -> int — integer addition. Left-associative operator, see Ocaml_operators for more information.
  • val (-) : int -> int -> int — integer subtraction. Left-associative operator, see Ocaml_operators for more information.
  • val ( * ) : int -> int -> int — integer multiplication. Left-associative operator, see Ocaml_operators for more information.
  • val (/) : int -> int -> int — integer division. 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). Left-associative operator, see Ocaml_operators for more information. Raises Division_by_zero if the second argument is 0. math with rules, okay 🧮.
  • val (mod) : int -> int -> int — integer remainder. If y is not zero, the result of x mod y satisfies the following properties: x = (x / y) * y + x mod y and abs(x mod y) <= abs(y) - 1. If y = 0, x mod y raises Division_by_zero. Note that x mod y is negative only if x < 0. Left-associative operator, see Ocaml_operators for more information. Raises Division_by_zero if y is zero. remainder lore, no cap 💀.
  • val abs : int -> int — abs x is the absolute value of x. On min_int this is min_int itself and thus remains negative. yes, really — that's the edge case, bestie 🚨.
  • val max_int : int — the greatest representable integer. the ceiling, literally 👑.
  • val min_int : int — (no description attached right here, bestie).

...the smallest representable integer 💀 that's min_int bestie, the literal floor of the int-iverse, no going lower, periodt.

🧮 Bitwise operations

okay so these are the bit-fiddling girlies ✨ they don't do math, they do vibes at the binary level, and honestly? iconic.

  • val (land) : int -> int -> int — bitwise logical and. It's a left-associative operator, and if you want the full tea on operator rules, check Ocaml_operators.
  • val (lor) : int -> int -> int — bitwise logical or. Left-associative operator too, see Ocaml_operators.
  • val (lxor) : int -> int -> int — bitwise logical exclusive or. Also left-associative operator, also Ocaml_operators.
  • val lnot : int -> int — bitwise logical negation. flips every bit, she's a hater like that 🙈
  • 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.
  • val (lsr) : int -> int -> int — n lsr m shifts n to the right by m bits. this one's a logical shift: zeroes get inserted no matter what the sign of n is. ⚠️ result is unspecified if m < 0 or m > Sys.int_size. Right-associative operator, see Ocaml_operators.
  • val (asr) : int -> int -> int — n asr m shifts n to the right by m bits, but this one's an arithmetic shift: the sign bit of n gets replicated (so negative stays negative, she remembers where she came from 🥺). ⚠️ result is unspecified if m < 0 or m > Sys.int_size. Right-associative operator, see Ocaml_operators.

🌊 Floating-point arithmetic

OCaml's floats follow the IEEE 754 standard, using double precision (64-bit) numbers. And here's the slay: floating-point operations never raise an exception on overflow, underflow, division by zero, etc. 💅 instead you get the special IEEE numbers, as appropriate — like infinity for 1.0 /. 0.0, neg_infinity for -1.0 /. 0.0, and nan ('not a number') for 0.0 /. 0.0.

Those special numbers then propagate through floating-point computations as expected: for instance, 1.0 /. infinity is 0.0, and basic arithmetic operations (+., -., *., /.) with nan as an argument return nan, …

  • val (~-.) : float -> float — unary negation. you can also write -. e instead of ~-. e. Unary operator, see Ocaml_operators.
  • val (~+.) : float -> float — unary addition. you can also write +. e instead of ~+. e. Unary operator, see Ocaml_operators. Since 3.12
  • val (+.) : float -> float -> float — floating-point addition. Left-associative operator, see Ocaml_operators.
  • val (-.) : float -> float -> float — floating-point subtraction. Left-associative operator, see Ocaml_operators.
  • val ( *. ) : float -> float -> float — floating-point multiplication. Left-associative operator, see Ocaml_operators.
  • val (/.) : float -> float -> float — floating-point division. Left-associative operator, see Ocaml_operators.
  • val ( ** ) : float -> float -> float — exponentiation. Right-associative operator, see Ocaml_operators.
  • val sqrt : float -> float — square root 🫶
  • val exp : float -> float — exponential.
  • val log : float -> float — natural logarithm.
  • val log10 : float -> float — base 10 logarithm.
  • val expm1 : float -> float — expm1 x computes exp x -. 1.0, giving numerically-accurate results even if x is close to 0.0. Since 3.12
  • 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
  • val cos : float -> float — cosine. the argument is in radians 🌸
  • val sin : float -> float — sine. argument in radians.
  • val tan : float -> float — tangent. argument in radians.
  • val acos : float -> float — arc cosine. the argument must fall within the range [-1.0, 1.0]. result is in radians and is between 0.0 and pi.
  • val asin : float -> float — arc sine. argument must fall within the range [-1.0, 1.0]. result is in radians and is between -pi/2 and pi/2.
  • val atan : float -> float — arc tangent. result is in radians and is between -pi/2 and pi/2.
  • val atan2 : float -> float -> float — atan2 y x returns the arc tangent of y /. x. the signs of x and y are used to determine the quadrant of the result 👑 result is in radians and is between -pi and pi.
  • val hypot : float -> float -> float — hypot x y returns sqrt(x *. x + y *. y), that is, the length of the hypotenuse of a right-angled triangle with sides of length x and y, or, equivalently, the distance of the point (x,y) to origin. if one of x or y is infinite, it returns infinity even if the other is nan 💀 Since 4.00
  • val cosh : float -> float — hyperbolic cosine.
  • val sinh : float -> float — hyperbolic sine.
  • val tanh : float -> float — hyperbolic tangent.
  • val acosh : float -> float — hyperbolic arc cosine. argument must fall within the range [1.0, inf]. result is in radians and is between 0.0 and inf. Since 4.13
  • val asinh : float -> float — hyperbolic arc sine. argument and result range over the entire real line. result is in radians. Since 4.13
  • val atanh : float -> float — hyperbolic arc tangent. argument must fall within the range [-1.0, 1.0]. result is in radians and ranges over the entire real line. Since 4.13
  • val ceil : float -> float — round above to an integer value. ceil f returns the least integer value greater than or equal to f. result comes back as a float.
  • val floor : float -> float — round below to an integer value. floor f returns the greatest integer value less than or equal to f. result comes back as a float.
  • val abs_float : float -> float — abs_float f returns the absolute value of f.
  • val copysign : float -> float -> float — copysign x y returns a float whose absolute value is that of x and whose sign is that of y. if x is nan, returns nan. if y is nan, returns either x or -. x, but it is not specified which 🙈 Since 4.00
  • 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 <= abs 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 float_of_int.
  • val float_of_int : int -> float — convert an integer to floating-point.
  • val truncate : float -> int — same as 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, unless otherwise specified in IEEE 754 standard. as for floating-point comparisons, =, <, <=, > and >= return false and <> returns true if one or both of their arguments is nan.
ngl this one's a glow-up: nan is a quiet NaN since 5.1; it was a signaling NaN before. she used to be loud 📢
  • val max_float : float — the largest positive finite value of type float.
  • val min_float : float — the smallest positive, non-zero, non-denormalized value of type float.
  • val epsilon_float : float — the difference between 1.0 and the smallest exactly representable floating-point number greater than 1.0.
type fpclass =
 | FP_normal  (* Normal number, none of the below *)
 | FP_subnormal  (* Number very close to 0.0, has reduced precision *)
 | FP_zero  (* Number is 0.0 or -0.0 *)
 | FP_infinite  (* Number is positive or negative infinity *)
 | FP_nan  (* Not a number: result of an undefined operation *)

the five classes of floating-point numbers, as determined by the classify_float function 💅

  • val classify_float : float -> fpclass — return the class of the given floating-point number: normal, subnormal, zero, infinite, or not a number.

🧵 String operations

more string operations are provided in module String 🎀

  • val (^) : string -> string -> string — string concatenation. Right-associative operator, see Ocaml_operators.
⚠️ raises Invalid_argument if the result is longer then than Sys.max_string_length bytes. (yes, the manpage really says "then than" 😭 we keep it, it's part of the lore)

🔤 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. ⚠️ raises Invalid_argument 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. since the returned values may be shared, the user should not modify them directly 🚨
  • val bool_of_string_opt : string -> bool option — convert the given string to a boolean. returns None if the string is not "true" or "false". Since 4.05
  • val bool_of_string : string -> bool — same as bool_of_string_opt, but raise Invalid_argument "bool_of_string" instead of returning None.
  • val string_of_int : int -> string — return the string representation of an integer, in decimal.
  • 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 string begins with 0u), in hexadecimal (if it begins with 0x or 0X), 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*max_int+1]. if the input exceeds max_int it is converted to the signed integer min_int + input - max_int - 1.

the _ (underscore) character can appear anywhere in the string and is ignored 💅 (she's just there for aesthetics, iykyk)

returns None 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. Since 4.05

  • val int_of_string : string -> int

...okay and that's literally where our page runs out 😭 the non-_opt twin is standing right at the edge of the section, so hold that thought bestie, she's got more to say and it's coming right up 💜

Same as int_of_string_opt, but it raises Failure "int_of_string" instead of returning None. 💅 (yes bestie, that’s the whole plot.)

val string_of_float : float -> string — returns a string representation of a floating-point number. This conversion can involve a loss of precision, so don’t come for me if your float gets a little fuzzy. For greater control over the manner in which the number is printed, see Printf. ✨

val float_of_string_opt : string -> float option — converts 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 an hexadecimal digit and d for a decimal digit.

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

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

Depending on the execution platforms, other representations of floating-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.

val float_of_string : string -> float — same as float_of_string_opt, but it raises Failure "float_of_string" instead of returning None.

✨ Pair operations ✨

val fst : 'a * 'b -> 'a — returns the first component of a pair. Slay.

val snd : 'a * 'b -> 'b — returns the second component of a pair. Also slay.

✨ List operations ✨

More list operations are provided in module List. 💖

val (@) : 'a list -> 'a list -> 'a list — l0 @ l1 appends l1 to l0. Same function as List.append. Right-associative operator, see Ocaml_operators for more information.

Since 5.1 this function is tail-recursive. 🔥

✨ Input/output ✨

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

type in_channel — the type of input channel.

type out_channel — the type of output channel.

val stdin : in_channel — the standard input for the process.

val stdout : out_channel — the standard output for the process.

val stderr : out_channel — the standard error output for the process.

✨ Output functions on standard output ✨

val print_char : char -> unit — prints a character on standard output.

val print_string : string -> unit — prints a string on standard output.

val print_bytes : bytes -> unit — prints a byte sequence on standard output.

Since 4.02.

val print_int : int -> unit — prints an integer, in decimal, on standard output.

val print_float : float -> unit — prints a floating-point number, in decimal, on standard output. The conversion of the number to a string uses string_of_float and can involve a loss of precision.

val print_endline : string -> unit — prints a string, followed by a newline character, on standard output and flushes standard output. 🎀

val print_newline : unit -> unit — prints a newline character on standard output, and flushes standard output. This can be used to simulate line buffering of standard output.

✨ Output functions on standard error ✨

val prerr_char : char -> unit — prints a character on standard error.

val prerr_string : string -> unit — prints a string on standard error.

val prerr_bytes : bytes -> unit — prints a byte sequence on standard error.

Since 4.02.

val prerr_int : int -> unit — prints an integer, in decimal, on standard error.

val prerr_float : float -> unit — prints a floating-point number, in decimal, on standard error. The conversion of the number to a string uses string_of_float and can involve a loss of precision.

val prerr_endline : string -> unit — prints a string, followed by a newline character on standard error and flushes standard error.

val prerr_newline : unit -> unit — prints a newline character on standard error, and flushes standard error.

✨ Input functions on standard input ✨

val read_line : unit -> string — flushes standard output, then reads characters from standard input until a newline character is encountered. Returns the string of all characters read, without the newline character at the end. Raises End_of_file if the end of the file is reached at the beginning of line. 🫶

val read_int_opt : unit -> int option — flushes standard output, then reads one line from standard input and converts it to an integer. Returns None if the line read is not a valid representation of an integer.

Since 4.05.

val read_int : unit -> int — same as read_int_opt, but it raises Failure "int_of_string" instead of returning None.

val read_float_opt : unit -> float option — flushes standard output, then reads one line from standard input and converts it to a floating-point number. Returns None if the line read is not a valid representation of a floating-point number.

Since 4.05.

val read_float : unit -> float — same as read_float_opt, but it raises Failure "float_of_string" instead of returning None.

✨ General output functions ✨

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

Opening modes for open_out_gen and open_in_gen.

val open_out : string -> out_channel — opens the named file for writing, and returns a new output channel on that file, positioned 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 exist.

val open_out_bin : string -> out_channel — same as open_out, but the file is opened in binary mode, so that no translation takes place during writes. On operating systems that do not distinguish between text mode and binary mode, this function behaves like open_out.

val open_out_gen : open_flag list -> int -> string -> out_channel — open_out_gen mode perm filename opens the named file for writing, as described above. The extra argument mode specifies the opening mode. The extra argument perm specifies the file permissions, in case the file must be created. open_out and open_out_bin are special cases of this function.

val flush : out_channel -> unit — flushes 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 — flushes all open output channels; ignore errors.

val output_char : out_channel -> char -> unit — writes the character on the given output channel.

val output_string : out_channel -> string -> unit — writes the string on the given output channel.

val output_bytes : out_channel -> bytes -> unit — writes the byte sequence on the given output channel.

Since 4.02.

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. Raises Invalid_argument if pos and len do not designate a valid range of buf.

val output_substring : out_channel -> string -> int -> int -> unit — same as output but takes a string as argument instead of a byte sequence.

Since 4.02.

val output_byte : out_channel -> int -> unit — writes 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 — writes one integer in binary format (4 bytes, big-endian) on the given output channel. The given integer is taken modulo 2^32. The only reliable way to read it back is through the input_binary_int function. The format is compatible across all machines for a given version of OCaml.

val output_value : out_channel -> 'a -> unit — writes the representation of a structured value of any type to a channel. Circularities and sharing inside the value are detected and preserved. The object can be read back, by the function input_value. See the description of module Marshal for more information. output_value is equivalent to Marshal.to_channel with an empty list of flags. 🧚

val seek_out : out_channel -> int -> unit — seek_out chan pos sets the current writing position to pos for channel chan. This works only for regular files. On files of other kinds (such as terminals, pipes and sockets), the behavior is unspecified. 🙈

val pos_out : out_channel -> int — returns the current writing position for the given channel. Does not work on channels opened with the Open_append flag (returns unspecified results). For files opened in text mode under Windows, the returned position is approximate (owing to end-of-line conversion); in particular, saving the current position with pos_out, then going back to this position using seek_out will not work. For this programming idiom to work reliably and portably, the file must be opened in binary mode. 💀

val out_channel_length : out_channel -> int — returns the size (number of characters) of the regular file on which the given channel is opened. If the channel is opened on a file that is not a regular file, the result is meaningless.

val close_out : out_channel -> unit — closes the given channel, flushing all buffered write operations. Output functions raise a Sys_error exception when they are applied to a closed output channel, except close_out and flush, which do nothing when applied to an already closed channel. Note that close_out may raise Sys_error if the operating system signals an error when flushing or closing.

val close_out_noerr : out_channel -> unit — same as close_out, but ignore all errors.

val set_binary_mode_out : out_channel -> bool -> unit — set_binary_mode_out oc true sets the channel oc to binary mode: no translations take place during output. set_binary_mode_out oc false sets the channel oc to text mode: depending on the operating system, some translations may take place during output. For instance, under Windows, end-of-lines will be translated from \n to \r\n. This function has no effect under operating systems that do not distinguish between text mode and binary mode. 🌈

✨ General input functions ✨

val open_in : string -> in_channel — opens the named file for reading, and returns a new input channel on that file, positioned at the beginning of the file. 👑

  • val open_in_bin : string -> in_channel — okay so this is literally open_in but the file opens in binary mode, meaning no translation happens during reads ✨ On operating systems that don't distinguish text mode vs binary mode, this behaves exactly like open_in, no cap.
  • 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 args mode and perm specify the opening mode and file permissions. open_in and open_in_bin are special cases of this function 💅
  • val input_char : in_channel -> char — reads one character from the given input channel. Raises End_of_file if there are no more characters to read 😭
  • val input_line : in_channel -> string — reads characters from the given input channel until a newline character is encountered. Returns the string of all characters read, without the newline character at the end 🎀 Raises End_of_file if the end of the file is reached at the beginning of a line.
  • val input : in_channel -> bytes -> int -> int -> int — input ic buf pos len reads up to len characters from the given channel ic, storing them in byte sequence 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 the end of file was reached. A return value between 0 and len exclusive means 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 really_input for reading exactly len characters.) Exception Invalid_argument "input" is raised if pos and len do not designate a valid range of buf 🙈
  • 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. Raises End_of_file if the end of file is reached before len characters have been read. Raises Invalid_argument if pos and len do not designate a valid range of buf 💀
  • val really_input_string : in_channel -> int -> string — really_input_string ic len reads len characters from channel ic and returns them in a new string. Since 4.02 ✨ Raises End_of_file if the end of file is reached before len characters have been read.
  • val input_byte : in_channel -> int — same as input_char, but returns the 8-bit integer representing the character. Raises End_of_file if the end of file was reached.
  • val input_binary_int : in_channel -> int — reads an integer encoded in binary format (4 bytes, big-endian) from the given input channel. See output_binary_int. Raises End_of_file if the end of file was reached while reading the integer 🫶
  • val input_value : in_channel -> 'a — reads the representation of a structured value, as produced by output_value, and returns 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. > ⚠️ bestie please vibe-check your types here, fr fr — it is literally not type-safe 😭
  • 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 — returns the current reading position for the given channel. For files opened in text mode under Windows, the returned position is approximate (owing to end-of-line conversion); in particular, saving the current position with pos_in, then going back to this position using seek_in will not work. For this programming idiom to work reliably and portably, the file must be opened in binary mode 💅
  • val in_channel_length : in_channel -> int — returns the size (number of characters) of the regular file on which the given channel is opened. If the channel is opened on a file that is not a regular file, the result is meaningless. The returned size does not take into account the end-of-line translations that can be performed when reading from a channel opened in text mode 🎀
  • val close_in : in_channel -> unit — closes 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 ✨
  • val close_in_noerr : in_channel -> unit — same as close_in, but ignore all errors 🙈
  • val set_binary_mode_in : in_channel -> bool -> unit — set_binary_mode_in ic true sets the channel ic to binary mode: no translations take place during input. set_binary_mode_out ic false sets the channel ic to text mode: depending on the operating system, some translations may take place during input. For instance, under Windows, end-of-lines will be translated from \r\n to \n. This function has no effect under operating systems that do not distinguish between text mode and binary mode 🦋

🦋 Operations on large files 🦋

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

🌈 References 🌈

type 'a ref = {
  mutable contents : 'a ;
}

The type of references (mutable indirection cells) containing a value of type 'a 💖

  • val ref : 'a -> 'a ref — returns 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. Unary operator, see Ocaml_operators for more information 👑
  • 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 💅
  • val incr : int ref -> unit — increments the integer contained in the given reference. Equivalent to fun r -> r := succ !r 🌸
  • val decr : int ref -> unit — decrements the integer contained in the given reference. Equivalent to fun r -> r := pred !r 🎀

💜 Result type 💜

type ('a, 'b) result =
 | Ok of 'a
 | Error of 'b

Since 4.03 ✨

🧚 Operations on format strings 🧚

Format strings are character strings with special lexical conventions that defines the functionality of formatted input/output functions. Format strings are used to read data with formatted input functions from module Scanf and to print data with formatted output functions from modules Printf 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 to read or print,
  • -formatting indications, introduced by the special character '@' followed by one or more characters specifying how to read or print the argument,
  • -plain characters that are regular characters with usual lexical conventions. Plain characters specify string literals to be read in the input 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, "%%" is considered as a plain '%' and "%@" as a plain '@' 💅

For more information about conversion specifications and formatting indications 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 are included for backward compatibility with earlier releases of OCaml 🦋

The meaning of format string type parameters is as follows:

  • 'a is the type of the parameters of the format for formatted output functions (printf-style functions); 'a is the type of the values read by the format for formatted input functions (scanf-style functions).
  • 'b is the type of input source for formatted input functions and the type of output target for formatted output functions. For printf-style functions from module Printf, 'b is typically out_channel; for printf-style functions from module Format, 'b is typically Format.formatter; for scanf-style functions from module Scanf, 'b is typically Scanf.Scanning.in_channel. Type argument 'b is also the type of the first argument given to user'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 printing functions, and also the type of the argument transmitted to the first argument of kprintf-style functions or to the kscanf-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 function invocation: for the printf-style functions, it is typically unit; for the scanf-style functions, it is typically the result type of the receiver function.
type ('a, 'b, 'c, 'd, 'e, 'f) format6 = ('a, 'b, 'c, 'd, 'e, 'f)
CamlinternalFormatBasics.format6

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

type ('a, 'b, 'c) format = ('a, 'b, 'c, 'c) format4
  • val string_of_format : ('a, 'b, 'c, 'd, 'e, 'f) format6 -> string — converts a format string into a string ✨
  • val format_of_string : ('a, 'b, 'c, 'd, 'e, 'f) format6 -> ('a, 'b, 'c, 'd, 'e, 'f) format6 — format_of_string s returns a format string read from the string literal s. Note: format_of_string can not convert a string argument that is not a literal. If you need this functionality, use the more general Scanf.format_from_string function 🫶
  • 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 format strings f1 and f2. The result is a format string that behaves as the concatenation of format strings f1 and f2: in case of formatted output, it accepts arguments from f1, then arguments from f2; in case of formatted input, it returns results from f1, then results from f2. Right-associative operator, see Ocaml_operators for more information 👑

⭐ Program termination ⭐

  • val exit : int -> 'a

okay so this function literally terminates the process and hands the given status code back to the operating system: usually 0 means no errors, and a small positive integer means failure 😌 All open output channels are flushed with flush_all. Then the callbacks registered with Domain.at_exit are called, followed by the ones registered with at_exit 🫶

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 does any of the following:

  • -executes — it executes exit ✨
  • -terminates — it terminates, either normally or because of an uncaught exception 😭
  • -executes — it executes the C function caml_shutdown 🔥

The functions are called in 'last in, first out' order: the function most recently added with at_exit is called first. Periodt.

✨ Standard library modules ✨

  • module Arg : (module Stdlib__Arg) 🌸
  • module Array : (module Stdlib__Array)
  • module ArrayLabels : (module Stdlib__ArrayLabels)
  • module Atomic : (module Stdlib__Atomic)
  • module Bigarray : (module Stdlib__Bigarray)
  • module Bool : (module Stdlib__Bool)
  • module Buffer : (module Stdlib__Buffer)
  • module Bytes : (module Stdlib__Bytes)
  • module BytesLabels : (module Stdlib__BytesLabels)
  • module Callback : (module Stdlib__Callback)
  • module Char : (module Stdlib__Char)
  • module Complex : (module Stdlib__Complex)
  • module Condition : (module Stdlib__Condition)
  • module Digest : (module Stdlib__Digest)
  • module Domain : (module Stdlib__Domain) 👑
Alert unstable. The Domain interface may change in incompatible ways in the future.
  • module Dynarray : (module Stdlib__Dynarray)
  • module Pqueue : (module Stdlib__Pqueue)
  • module Effect : (module Stdlib__Effect) 🦋
Alert unstable. The Effect interface may change in incompatible ways in the future.
  • module Either : (module Stdlib__Either)
  • module Ephemeron : (module Stdlib__Ephemeron)
  • module Filename : (module Stdlib__Filename)
  • module Float : (module Stdlib__Float)
  • module Format : (module Stdlib__Format)
  • module Fun : (module Stdlib__Fun)
  • module Gc : (module Stdlib__Gc)
  • module Hashtbl : (module Stdlib__Hashtbl)
  • module Iarray : (module Stdlib__Iarray)
  • module In_channel : (module Stdlib__In_channel)
  • module Int : (module Stdlib__Int)
  • module Int32 : (module Stdlib__Int32)
  • module Int64 : (module Stdlib__Int64)
  • module Lazy : (module Stdlib__Lazy)
  • module Lexing : (module Stdlib__Lexing)
  • module List : (module Stdlib__List)
  • module ListLabels : (module Stdlib__ListLabels)
  • module Map : (module Stdlib__Map)
  • module Marshal : (module Stdlib__Marshal)
  • module MoreLabels : (module Stdlib__MoreLabels)
  • module Mutex : (module Stdlib__Mutex)
  • module Nativeint : (module Stdlib__Nativeint)
  • module Obj : (module Stdlib__Obj)
  • module Oo : (module Stdlib__Oo)
  • module Option : (module Stdlib__Option)
  • module Out_channel : (module Stdlib__Out_channel)
  • module Pair : (module Stdlib__Pair)
  • module Parsing : (module Stdlib__Parsing)
  • module Printexc : (module Stdlib__Printexc)
  • module Printf : (module Stdlib__Printf)
  • module Queue : (module Stdlib__Queue)
  • module Random : (module Stdlib__Random)
  • module Result : (module Stdlib__Result)
  • module Repr : (module Stdlib__Repr)
  • module Scanf : (module Stdlib__Scanf)
  • module Semaphore : (module Stdlib__Semaphore)
  • module Seq : (module Stdlib__Seq)
  • module Set : (module Stdlib__Set)
  • module Stack : (module Stdlib__Stack)
  • module StdLabels : (module Stdlib__StdLabels)
  • module String : (module Stdlib__String)
  • module StringLabels : (module Stdlib__StringLabels)
  • module Sys : (module Stdlib__Sys)
  • module Type : (module Stdlib__Type)
  • module Uchar : (module Stdlib__Uchar)
  • module Unit : (module Stdlib__Unit)
  • module Weak : (module Stdlib__Weak) 💖

🎀 that's the whole page, bestie. Source/version: OCamldoc; date: 2026-06-22; and yeah, it's Stdlib(3) — periodt. 💅

📦 where this page comes from