Below is the API for the OCaml standard library. It's directly copied over from the OCaml Manual, formatted to the Reason syntax and styled accordingly. The API docs are work-in-progress; we'll be polishing these gradually!

If you're targeting JavaScript, the API docs for BuckleScript includes all of below, plus JS-specific APIs.

`module Pervasives: sig .. end`

The initially opened module.

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

This module is automatically opened at the beginning of each compilation.
All components of this module can therefore be referred by their short
name, without prefixing them by `Pervasives`

.

```
let raise: exn => 'a;
```

Raise the given exception value

```
let raise_notrace: exn => 'a;
```

A faster version

**Since** 4.02.0

`raise`

which does not record the backtrace.```
let invalid_arg: string => 'a;
```

Raise exception

`Invalid_argument`

with the given string.```
let failwith: string => 'a;
```

Raise exception

`Failure`

with the given string.```
exception Exit;
```

The

`Exit`

exception is not raised by any library function. It is
provided for use in your programs.```
let (==): ('a, 'a) => bool;
```

`e1 = e2`

tests for structural equality of `e1`

and `e2`

.
Mutable structures (e.g. references and arrays) are equal
if and only if their current contents are structurally equal,
even if the two mutable objects are not the same physical object.
Equality between functional values raises `Invalid_argument`

.
Equality between cyclic data structures may not terminate.```
let (!=): ('a, 'a) => bool;
```

Negation of

`Pervasives.(=)`

.```
let (<): ('a, 'a) => bool;
```

See

`Pervasives.(>=)`

.```
let (>): ('a, 'a) => bool;
```

See

`Pervasives.(>=)`

.```
let (<=): ('a, 'a) => bool;
```

See

`Pervasives.(>=)`

.```
let (>=): ('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

`( = )`

. As in the case
of `( = )`

, mutable structures are compared by contents.
Comparison between functional values raises `Invalid_argument`

.
Comparison between cyclic structures may not terminate.```
let compare: ('a, 'a) => int;
```

`compare x y`

returns `0`

if `x`

is equal to `y`

,
a negative integer if `x`

is less than `y`

, and a positive integer
if `x`

is greater than `y`

. The ordering implemented by `compare`

is compatible with the comparison predicates `=`

, `<`

and `>`

defined above, with one difference on the treatment of the float value
`Pervasives.nan`

. Namely, the comparison predicates treat `nan`

as different from any other float value, including itself;
while `compare`

treats `nan`

as equal to itself and less than any
other float value. This treatment of `nan`

ensures that `compare`

defines a total ordering relation.
`compare`

applied to functional values may raise `Invalid_argument`

.
`compare`

applied to cyclic structures may not terminate.

The `compare`

function can be used as the comparison function
required by the `Set.Make`

and `Map.Make`

functors, as well as
the `List.sort`

and `Array.sort`

functions.

```
let min: ('a, 'a) => 'a;
```

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

`nan`

.```
let max: ('a, 'a) => 'a;
```

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

`nan`

.```
let (===): ('a, 'a) => bool;
```

`e1 == e2`

tests for physical equality of `e1`

and `e2`

.
On mutable types such as references, arrays, byte sequences, records with
mutable fields and objects with mutable instance variables,
`e1 == e2`

is true if and only if physical modification of `e1`

also affects `e2`

.
On non-mutable types, the behavior of `( == )`

is
implementation-dependent; however, it is guaranteed that
`e1 == e2`

implies `compare e1 e2 = 0`

.```
let (!==): ('a, 'a) => bool;
```

Negation of

`Pervasives.(==)`

.```
let (!): bool => bool;
```

The boolean negation.

```
let (&&): (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.```
let (&): (bool, bool) => bool;
```

```
let (||): (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.```
let (or): (bool, bool) => bool;
```

```
let __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".```
let __FILE__: string;
```

`__FILE__`

returns the name of the file currently being
parsed by the compiler.```
let __LINE__: int;
```

`__LINE__`

returns the line number at which this expression
appears in the file currently being parsed by the compiler.```
let __MODULE__: string;
```

`__MODULE__`

returns the module name of the file being
parsed by the compiler.```
let __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.```
let __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".```
let __LINE_OF__: 'a => (int, 'a);
```

`__LINE__ 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.```
let __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.```
let (|>): ('a, 'a => 'b) => 'b;
```

Reverse-application operator:

**Since** 4.01

`x |> f |> g`

is exactly equivalent
to `g (f (x))`

.```
let (@@): ('a => 'b, 'a) => 'b;
```

Application operator:

**Since** 4.01

`g @@ f @@ x`

is exactly equivalent to
`g (f (x))`

.Integers are 31 bits wide (or 63 bits on 64-bit processors). All operations are taken modulo 2

```
let (~-): int => int;
```

Unary negation. You can also write

`- e`

instead of `~- e`

.```
let (~+): int => int;
```

Unary addition. You can also write

**Since** 3.12.0

`+ e`

instead of `~+ e`

.```
let succ: int => int;
```

`succ x`

is `x + 1`

.```
let pred: int => int;
```

`pred x`

is `x - 1`

.```
let (+): (int, int) => int;
```

Integer addition.

```
let (-): (int, int) => int;
```

Integer subtraction.

```
let ( * ): (int, int) => int;
```

Integer multiplication.

```
let (/): (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)`

.```
let (mod): (int, int) => int;
```

Integer remainder. If

`y`

is not zero, the result
of `x mod y`

satisfies the following properties:
`x = (x / y) * y + x mod y`

and
`abs(x mod y) <= abs(y) - 1`

.
If `y = 0`

, `x mod y`

raises `Division_by_zero`

.
Note that `x mod y`

is negative only if `x < 0`

.
Raise `Division_by_zero`

if `y`

is zero.```
let abs: int => int;
```

Return the absolute value of the argument. Note that this may be
negative if the argument is

`min_int`

.```
let max_int: int;
```

The greatest representable integer.

```
let min_int: int;
```

The smallest representable integer.

Bitwise operations

```
let (land): (int, int) => int;
```

Bitwise logical and.

```
let (lor): (int, int) => int;
```

Bitwise logical or.

```
let (lxor): (int, int) => int;
```

Bitwise logical exclusive or.

```
let lnot: int => int;
```

Bitwise logical negation.

```
let (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.```
let (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`

.```
let (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`

.
OCaml's floating-point numbers follow the
IEEE 754 standard, using double precision (64 bits) numbers.
Floating-point operations never raise an exception on overflow,
underflow, division by zero, etc. Instead, special IEEE numbers
are returned as appropriate, such as `infinity`

for `1.0 /. 0.0`

,
`neg_infinity`

for `-1.0 /. 0.0`

, and `nan`

('not a number')
for `0.0 /. 0.0`

. These special numbers then propagate through
floating-point computations as expected: for instance,
`1.0 /. infinity`

is `0.0`

, and any arithmetic operation with `nan`

as argument returns `nan`

as result.

```
let (~-.): float => float;
```

Unary negation. You can also write

`-. e`

instead of `~-. e`

.```
let (~+.): float => float;
```

Unary addition. You can also write

**Since** 3.12.0

`+. e`

instead of `~+. e`

.```
let (+.): (float, float) => float;
```

Floating-point addition

```
let (-.): (float, float) => float;
```

Floating-point subtraction

```
let ( *. ): (float, float) => float;
```

Floating-point multiplication

```
let (/.): (float, float) => float;
```

Floating-point division.

```
let ( ** ): (float, float) => float;
```

Exponentiation.

```
let sqrt: float => float;
```

Square root.

```
let exp: float => float;
```

Exponential.

```
let log: float => float;
```

Natural logarithm.

```
let log10: float => float;
```

Base 10 logarithm.

```
let expm1: float => float;
```

`expm1 x`

computes `exp x -. 1.0`

, giving numerically-accurate results
even if `x`

is close to `0.0`

.```
let log1p: float => float;
```

`log1p x`

computes `log(1.0 +. x)`

(natural logarithm),
giving numerically-accurate results even if `x`

is close to `0.0`

.```
let cos: float => float;
```

Cosine. Argument is in radians.

```
let sin: float => float;
```

Sine. Argument is in radians.

```
let tan: float => float;
```

Tangent. Argument is in radians.

```
let 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`

.```
let 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`

.```
let atan: float => float;
```

Arc tangent.
Result is in radians and is between

`-pi/2`

and `pi/2`

.```
let 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`

.```
let 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.```
let cosh: float => float;
```

Hyperbolic cosine. Argument is in radians.

```
let sinh: float => float;
```

Hyperbolic sine. Argument is in radians.

```
let tanh: float => float;
```

Hyperbolic tangent. Argument is in radians.

```
let 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.```
let floor: float => float;
```

Round below to an integer value.

`floor f`

returns the greatest integer value less than or
equal to `f`

.
The result is returned as a float.```
let abs_float: float => float;
```

`abs_float f`

returns the absolute value of `f`

.```
let 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.```
let 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.```
let 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`

.```
let ldexp: (float, int) => float;
```

`ldexp x n`

returns `x *. 2 ** n`

.```
let modf: float => (float, float);
```

`modf f`

returns the pair of the fractional and integral
part of `f`

.```
let float: int => float;
```

Same as

`Pervasives.float_of_int`

.```
let float_of_int: int => float;
```

Convert an integer to floating-point.

```
let truncate: float => int;
```

Same as

`Pervasives.int_of_float`

.```
let 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.```
let infinity: float;
```

Positive infinity.

```
let neg_infinity: float;
```

Negative infinity.

```
let 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`

.```
let max_float: float;
```

The largest positive finite value of type

`float`

.```
let min_float: float;
```

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

`float`

.```
let epsilon_float: float;
```

The difference between

`1.0`

and the smallest exactly representable
floating-point number greater than `1.0`

.`type fpclass = `

`|` |
`FP_normal` |
`(*` |
Normal number, none of the below
| `*)` |

`|` |
`FP_subnormal` |
`(*` |
Number very close to 0.0, has reduced precision
| `*)` |

`|` |
`FP_zero` |
`(*` |
Number is 0.0 or -0.0
| `*)` |

`|` |
`FP_infinite` |
`(*` |
Number is positive or negative infinity
| `*)` |

`|` |
`FP_nan` |
`(*` |
Not a number: result of an undefined operation
| `*)` |

The five classes of floating-point numbers, as determined by
the

`Pervasives.classify_float`

function.```
let classify_float: float => fpclass;
```

Return the class of the given floating-point number:
normal, subnormal, zero, infinite, or not a number.

More string operations are provided in module `String`

.

```
let (++): (string, string) => string;
```

String concatenation.

More character operations are provided in module `Char`

.

```
let int_of_char: char => int;
```

Return the ASCII code of the argument.

```
let 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.```
let 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.```
let string_of_bool: bool => string;
```

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

```
let 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"`

.```
let string_of_int: int => string;
```

Return the string representation of an integer, in decimal.

```
let 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`

.```
let string_of_float: float => string;
```

Return the string representation of a floating-point number.

```
let 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.```
let fst: (('a, 'b)) => 'a;
```

Return the first component of a pair.

```
let snd: (('a, 'b)) => 'b;
```

Return the second component of a pair.

More list operations are provided in module `List`

.

```
let (@): (list('a), list('a)) => list('a);
```

List concatenation.

`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.

```
let stdin: in_channel;
```

The standard input for the process.

```
let stdout: out_channel;
```

The standard output for the process.

```
let stderr: out_channel;
```

The standard error output for the process.

Output functions on standard output

```
let print_char: char => unit;
```

Print a character on standard output.

```
let print_string: string => unit;
```

Print a string on standard output.

```
let print_bytes: bytes => unit;
```

Print a byte sequence on standard output.

**Since** 4.02.0

```
let print_int: int => unit;
```

Print an integer, in decimal, on standard output.

```
let print_float: float => unit;
```

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

```
let print_endline: string => unit;
```

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

```
let print_newline: unit => unit;
```

Print a newline character on standard output, and flush
standard output. This can be used to simulate line
buffering of standard output.

Output functions on standard error

```
let prerr_char: char => unit;
```

Print a character on standard error.

```
let prerr_string: string => unit;
```

Print a string on standard error.

```
let prerr_bytes: bytes => unit;
```

Print a byte sequence on standard error.

**Since** 4.02.0

```
let prerr_int: int => unit;
```

Print an integer, in decimal, on standard error.

```
let prerr_float: float => unit;
```

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

```
let prerr_endline: string => unit;
```

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

```
let prerr_newline: unit => unit;
```

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

Input functions on standard input

```
let 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.

```
let 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.```
let read_float: unit => float;
```

Flush standard output, then read one line from standard input
and convert it to a floating-point number.
The result is unspecified if the line read is not a valid
representation of a floating-point number.

General output functions

`type open_flag = `

`|` |
`Open_rdonly` |
`(*` |
open for reading.
| `*)` |

`|` |
`Open_wronly` |
`(*` |
open for writing.
| `*)` |

`|` |
`Open_append` |
`(*` |
open for appending: always write at end of file.
| `*)` |

`|` |
`Open_creat` |
`(*` |
create the file if it does not exist.
| `*)` |

`|` |
`Open_trunc` |
`(*` |
empty the file if it already exists.
| `*)` |

`|` |
`Open_excl` |
`(*` |
fail if Open_creat and the file already exists.
| `*)` |

`|` |
`Open_binary` |
`(*` |
open in binary mode (no conversion).
| `*)` |

`|` |
`Open_text` |
`(*` |
open in text mode (may perform conversions).
| `*)` |

`|` |
`Open_nonblock` |
`(*` |
open in non-blocking mode.
| `*)` |

```
let open_out: string => out_channel;
```

Open the named file for writing, and return a new output channel
on that file, positionned at the beginning of the file. The
file is truncated to zero length if it already exists. It
is created if it does not already exists.

```
let open_out_bin: string => out_channel;
```

Same as

`Pervasives.open_out`

, but the file is opened in binary mode,
so that no translation takes place during writes. On operating
systems that do not distinguish between text mode and binary
mode, this function behaves like `Pervasives.open_out`

.```
let open_out_gen: (list(open_flag), int, string) => out_channel;
```

`open_out_gen mode perm filename`

opens the named file for writing,
as described above. The extra argument `mode`

specify the opening mode. The extra argument `perm`

specifies
the file permissions, in case the file must be created.
`Pervasives.open_out`

and `Pervasives.open_out_bin`

are special
cases of this function.```
let flush: out_channel => unit;
```

Flush the buffer associated with the given output channel,
performing all pending writes on that channel.
Interactive programs must be careful about flushing standard
output and standard error at the right time.

```
let flush_all: unit => unit;
```

Flush all open output channels; ignore errors.

```
let output_char: (out_channel, char) => unit;
```

Write the character on the given output channel.

```
let output_string: (out_channel, string) => unit;
```

Write the string on the given output channel.

```
let output_bytes: (out_channel, bytes) => unit;
```

Write the byte sequence on the given output channel.

**Since** 4.02.0

```
let 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 not
designate a valid range of `buf`

.```
let output_substring: (out_channel, string, int, int) => unit;
```

Same as

**Since** 4.02.0

`output`

but take a string as argument instead of
a byte sequence.```
let output_byte: (out_channel, int) => unit;
```

Write one 8-bit integer (as the single character with that code)
on the given output channel. The given integer is taken modulo
256.

```
let output_binary_int: (out_channel, int) => unit;
```

Write one integer in binary format (4 bytes, big-endian)
on the given output channel.
The given integer is taken modulo 2^{32}.
The only reliable way to read it back is through the

`Pervasives.input_binary_int`

function. The format is compatible across
all machines for a given version of OCaml.```
let output_value: (out_channel, 'a) => unit;
```

Write the representation of a structured value of any type
to a channel. Circularities and sharing inside the value
are detected and preserved. The object can be read back,
by the function

`Pervasives.input_value`

. See the description of module
`Marshal`

for more information. `Pervasives.output_value`

is equivalent
to `Marshal.to_channel`

with an empty list of flags.```
let 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.```
let pos_out: out_channel => int;
```

Return the current writing position for the given channel. Does
not work on channels opened with the

`Open_append`

flag (returns
unspecified results).```
let out_channel_length: out_channel => int;
```

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

```
let close_out: out_channel => unit;
```

Close the given channel, flushing all buffered write operations.
Output functions raise a

`Sys_error`

exception when they are
applied to a closed output channel, except `close_out`

and `flush`

,
which do nothing when applied to an already closed channel.
Note that `close_out`

may raise `Sys_error`

if the operating
system signals an error when flushing or closing.```
let close_out_noerr: out_channel => unit;
```

Same as

`close_out`

, but ignore all errors.```
let 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

```
let open_in: string => in_channel;
```

Open the named file for reading, and return a new input channel
on that file, positionned at the beginning of the file.

```
let open_in_bin: string => in_channel;
```

Same as

`Pervasives.open_in`

, but the file is opened in binary mode,
so that no translation takes place during reads. On operating
systems that do not distinguish between text mode and binary
mode, this function behaves like `Pervasives.open_in`

.```
let open_in_gen: (list(open_flag), int, string) => in_channel;
```

`open_in_gen mode perm filename`

opens the named file for reading,
as described above. The extra arguments
`mode`

and `perm`

specify the opening mode and file permissions.
`Pervasives.open_in`

and `Pervasives.open_in_bin`

are special
cases of this function.```
let 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.```
let input_line: in_channel => string;
```

Read characters from the given input channel, until a
newline character is encountered. Return the string of
all characters read, without the newline character at the end.
Raise

`End_of_file`

if the end of the file is reached
at the beginning of line.```
let 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 that the end of file was reached.
A return value between 0 and `len`

exclusive means that
not all requested `len`

characters were read, either because
no more characters were available at that time, or because
the implementation found it convenient to do a partial read;
`input`

must be called again to read the remaining characters,
if desired. (See also `Pervasives.really_input`

for reading
exactly `len`

characters.)
Exception `Invalid_argument "input"`

is raised if `pos`

and `len`

do not designate a valid range of `buf`

.```
let 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 `len`

characters have been read.
Raise `Invalid_argument "really_input"`

if
`pos`

and `len`

do not designate a valid range of `buf`

.```
let 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.
Raise `End_of_file`

if the end of file is reached before `len`

characters have been read.```
let input_byte: in_channel => int;
```

Same as

`Pervasives.input_char`

, but return the 8-bit integer representing
the character.
Raise `End_of_file`

if an end of file was reached.```
let input_binary_int: in_channel => int;
```

Read an integer encoded in binary format (4 bytes, big-endian)
from the given input channel. See

`Pervasives.output_binary_int`

.
Raise `End_of_file`

if an end of file was reached while reading the
integer.```
let input_value: in_channel => 'a;
```

Read the representation of a structured value, as produced
by

`Pervasives.output_value`

, and return the corresponding value.
This function is identical to `Marshal.from_channel`

;
see the description of module `Marshal`

for more information,
in particular concerning the lack of type safety.```
let 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.```
let pos_in: in_channel => int;
```

Return the current reading position for the given channel.

```
let in_channel_length: in_channel => int;
```

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

```
let close_in: in_channel => unit;
```

Close the given channel. Input functions raise a

`Sys_error`

exception when they are applied to a closed input channel,
except `close_in`

, which does nothing when applied to an already
closed channel.```
let close_in_noerr: in_channel => unit;
```

Same as

`close_in`

, but ignore all errors.```
let 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.

`type 'a ref = {`

` ` |
`mutable contents : 'a;` |

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

`'a`

.```
let ref: 'a => ref('a);
```

Return a fresh reference containing the given value.

```
let (^): ref('a) => 'a;
```

`!r`

returns the current contents of reference `r`

.
Equivalent to `fun r -> r.contents`

.```
let (:=): (ref('a), 'a) => unit;
```

`r := a`

stores the value of `a`

in reference `r`

.
Equivalent to `fun r v -> r.contents <- v`

.```
let incr: ref(int) => unit;
```

Increment the integer contained in the given reference.
Equivalent to

`fun r -> r := succ !r`

.```
let decr: ref(int) => unit;
```

Decrement the integer contained in the given reference.
Equivalent to

`fun r -> r := pred !r`

.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.

`'%'`

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 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.

`'%'`

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`

.

`'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 format6('a, 'b, 'c, 'd, 'e, 'f) = CamlinternalFormatBasics.format6('a, 'b, 'c, 'd, 'e, 'f);
```

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

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

```
let string_of_format: format6('a, 'b, 'c, 'd, 'e, 'f) => string;
```

Converts a format string into a string.

```
let format_of_string: format6('a, 'b, 'c, 'd, 'e, 'f) => format6('a, 'b, 'c, 'd, 'e, 'f);
```

`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.```
let (^^):
(format6('a, 'b, 'c, 'd, 'e, 'f), format6('f, 'b, 'c, 'e, 'g, 'h)) =>
format6('a, 'b, 'c, 'd, 'g, 'h);
```

`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`

.```
let 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.```
let at_exit: (unit => unit) => unit;
```

Register the given function to be called at program
termination time. The functions registered with

`at_exit`

will be called when the program executes `Pervasives.exit`

,
or terminates, either normally or because of an uncaught exception.
The functions are called in 'last in, first out' order:
the function most recently added with `at_exit`

is called first.