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# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: 2021 The Elixir Team
# SPDX-FileCopyrightText: 2012 Plataformatec
# Use elixir_bootstrap module to be able to bootstrap Kernel.
# The bootstrap module provides simpler implementations of the
# functions removed, simple enough to bootstrap.
import Kernel,
except: [@: 1, defmodule: 2, def: 1, def: 2, defp: 2, defmacro: 1, defmacro: 2, defmacrop: 2]
import :elixir_bootstrap
defmodule Kernel do
@moduledoc """
`Kernel` is Elixir's default environment.
It mainly consists of:
* basic language primitives, such as arithmetic operators, spawning of processes,
data type handling, and others
* macros for control-flow and defining new functionality (modules, functions, and the like)
* guard checks for augmenting pattern matching
You can invoke `Kernel` functions and macros anywhere in Elixir code
without the use of the `Kernel.` prefix since they have all been
automatically imported. For example, in IEx, you can call:
iex> is_number(13)
true
If you don't want to import a function or macro from `Kernel`, use the `:except`
option and then list the function/macro by arity:
import Kernel, except: [if: 2, is_number: 1]
See `import/2` for more information on importing.
Elixir also has special forms that are always imported and
cannot be skipped. These are described in `Kernel.SpecialForms`.
## The standard library
`Kernel` provides the basic capabilities the Elixir standard library
is built on top of. It is recommended to explore the standard library
for advanced functionality. Here are the main groups of modules in the
standard library (this list is not a complete reference, see the
documentation sidebar for all entries).
### Built-in types
The following modules handle Elixir built-in data types:
* `Atom` - literal constants with a name (`true`, `false`, and `nil` are atoms)
* `Float` - numbers with floating point precision
* `Function` - a reference to code chunk, created with the `fn/1` special form
* `Integer` - whole numbers (not fractions)
* `List` - collections of a variable number of elements (linked lists)
* `Map` - collections of key-value pairs
* `Process` - light-weight threads of execution
* `Port` - mechanisms to interact with the external world
* `Tuple` - collections of a fixed number of elements
There are two data types without an accompanying module:
* Bitstring - a sequence of bits, created with `<<>>/1`.
When the number of bits is divisible by 8, they are called binaries and can
be manipulated with Erlang's [`:binary`](`:binary`) module
* Reference - a unique value in the runtime system, created with `make_ref/0`
### Data types
Elixir also provides other data types that are built on top of the types
listed above. Some of them are:
* `Date` - `year-month-day` structs in a given calendar
* `DateTime` - date and time with time zone in a given calendar
* `Exception` - data raised from errors and unexpected scenarios
* `MapSet` - unordered collections of unique elements
* `NaiveDateTime` - date and time without time zone in a given calendar
* `Keyword` - lists of two-element tuples, often representing optional values
* `Range` - inclusive ranges between two integers
* `Regex` - regular expressions
* `String` - UTF-8 encoded binaries representing characters
* `Time` - `hour:minute:second` structs in a given calendar
* `URI` - representation of URIs that identify resources
* `Version` - representation of versions and requirements
### System modules
Modules that interface with the underlying system, such as:
* `IO` - handles input and output
* `File` - interacts with the underlying file system
* `Path` - manipulates file system paths
* `System` - reads and writes system information
### Protocols
Protocols add polymorphic dispatch to Elixir. They are contracts
implementable by data types. See `Protocol` for more information on
protocols. Elixir provides the following protocols in the standard library:
* `Collectable` - collects data into a data type
* `Enumerable` - handles collections in Elixir. The `Enum` module
provides eager functions for working with collections, the `Stream`
module provides lazy functions
* `Inspect` - converts data types into their programming language
representation
* `List.Chars` - converts data types to their outside world
representation as charlists (non-programming based)
* `String.Chars` - converts data types to their outside world
representation as strings (non-programming based)
### Process-based and application-centric functionality
The following modules build on top of processes to provide concurrency,
fault-tolerance, and more.
* `Agent` - a process that encapsulates mutable state
* `Application` - functions for starting, stopping and configuring
applications
* `GenServer` - a generic client-server API
* `Registry` - a key-value process-based storage
* `Supervisor` - a process that is responsible for starting,
supervising and shutting down other processes
* `Task` - a process that performs computations
* `Task.Supervisor` - a supervisor for managing tasks exclusively
### Supporting documents
Under the "Pages" section in sidebar you will find tutorials, guides,
and reference documents that outline Elixir semantics and behaviors
in more detail. Those are:
* [Compatibility and deprecations](compatibility-and-deprecations.md) - lists
compatibility between every Elixir version and Erlang/OTP, release schema;
lists all deprecated functions, when they were deprecated and alternatives
* [Library guidelines](library-guidelines.md) - general guidelines, anti-patterns,
and rules for those writing libraries
* [Naming conventions](naming-conventions.md) - naming conventions for Elixir code
* [Operators reference](operators.md) - lists all Elixir operators and their precedences
* [Patterns and guards](patterns-and-guards.md) - an introduction to patterns,
guards, and extensions
* [Syntax reference](syntax-reference.md) - the language syntax reference
* [Typespecs reference](typespecs.md)- types and function specifications, including list of types
* [Unicode syntax](unicode-syntax.md) - outlines Elixir support for Unicode
## Guards
This module includes the built-in guards used by Elixir developers.
They are a predefined set of functions and macros that augment pattern
matching, typically invoked after the `when` operator. For example:
def drive(%User{age: age}) when age >= 16 do
...
end
The clause above will only be invoked if the user's age is more than
or equal to 16. Guards also support joining multiple conditions with
`and` and `or`. The whole guard is true if all guard expressions will
evaluate to `true`. A more complete introduction to guards is available
in the [Patterns and guards](patterns-and-guards.md) page.
## Truthy and falsy values
Besides the booleans `true` and `false`, Elixir has the
concept of a "truthy" or "falsy" value.
* a value is truthy when it is neither `false` nor `nil`
* a value is falsy when it is either `false` or `nil`
Elixir has functions, like `and/2`, that *only* work with
booleans, but also functions that work with these
truthy/falsy values, like `&&/2` and `!/1`.
## Structural comparison
The functions in this module perform structural comparison. This allows
different data types to be compared using comparison operators:
1 < :an_atom
This is possible so Elixir developers can create collections, such as
dictionaries and ordered sets, that store a mixture of data types in them.
To understand why this matters, let's discuss the two types of comparisons
we find in software: _structural_ and _semantic_.
Structural means we are comparing the underlying data structures and we often
want those operations to be as fast as possible, because it is used to power
several algorithms and data structures in the language. A semantic comparison
worries about what each data type represents. For example, semantically
speaking, it doesn't make sense to compare `Time` with `Date`.
One example that shows the differences between structural and semantic
comparisons are strings: "alien" sorts less than "office" (`"alien" < "office"`)
but "álien" is greater than "office". This happens because `<` compares the
underlying bytes that form the string. If you were doing alphabetical listing,
you may want "álien" to also appear before "office".
This means **comparisons in Elixir are structural**, as it has the goal
of comparing data types as efficiently as possible to create flexible
and performant data structures. This distinction is specially important
for functions that provide ordering, such as `>/2`, `</2`, `>=/2`,
`<=/2`, `min/2`, and `max/2`. For example:
~D[2017-03-31] > ~D[2017-04-01]
will return `true` because structural comparison compares the `:day`
field before `:month` or `:year`. Luckily, the Elixir compiler will
detect whenever comparing structs or whenever comparing code that is
either always true or false, and emit a warning accordingly.
In order to perform semantic comparisons, the relevant data-types
provide a `compare/2` function, such as `Date.compare/2`:
iex> Date.compare(~D[2017-03-31], ~D[2017-04-01])
:lt
Alternatively, you can use the functions in the `Enum` module to
sort or compute a maximum/minimum:
iex> Enum.sort([~D[2017-03-31], ~D[2017-04-01]], Date)
[~D[2017-03-31], ~D[2017-04-01]]
iex> Enum.max([~D[2017-03-31], ~D[2017-04-01]], Date)
~D[2017-04-01]
The second argument is precisely the module to be used for semantic
comparison. Keeping this distinction is important, because if semantic
comparison was used by default for implementing data structures and
algorithms, they could become orders of magnitude slower!
Finally, note there is an overall structural sorting order, called
"Term Ordering", defined below. This order is provided for reference
purposes, it is not required for Elixir developers to know it by heart.
### Term ordering
```
number < atom < reference < function < port < pid < tuple < map < list < bitstring
```
When comparing two numbers of different types (a number being either
an integer or a float), a conversion to the type with greater precision
will always occur, unless the comparison operator used is either `===/2`
or `!==/2`. A float will be considered more precise than an integer, unless
the float is greater/less than +/-9007199254740992.0 respectively,
at which point all the significant figures of the float are to the left
of the decimal point. This behavior exists so that the comparison of large
numbers remains transitive.
The collection types are compared using the following rules:
* Tuples are compared by size, then element by element.
* Maps are compared by size, then by key-value pairs.
* Lists are compared element by element.
* Bitstrings are compared byte by byte, incomplete bytes are compared bit by bit.
* Atoms are compared using their string value, codepoint by codepoint.
### Examples
We can check the truthiness of a value by using the `!/1`
function twice.
Truthy values:
iex> !!true
true
iex> !!5
true
iex> !![1,2]
true
iex> !!"foo"
true
Falsy values (of which there are exactly two):
iex> !!false
false
iex> !!nil
false
## Inlining
Some of the functions described in this module are inlined by
the Elixir compiler into their Erlang counterparts in the
[`:erlang`](`:erlang`) module.
Those functions are called BIFs (built-in internal functions)
in Erlang-land and they exhibit interesting properties, as some
of them are allowed in guards and others are used for compiler
optimizations.
Most of the inlined functions can be seen in effect when
capturing the function:
iex> &Kernel.is_atom/1
&:erlang.is_atom/1
Those functions will be explicitly marked in their docs as
"inlined by the compiler".
"""
# We need this check only for bootstrap purposes.
# Once Kernel is loaded and we recompile, it is a no-op.
@compile {:inline, bootstrapped?: 1}
case :code.ensure_loaded(Kernel) do
{:module, _} ->
defp bootstrapped?(module), do: is_atom(module)
{:error, _} ->
defp bootstrapped?(module), do: :code.ensure_loaded(module) == {:module, module}
end
## Delegations to Erlang with inlining (macros)
@doc """
Returns an integer or float which is the arithmetical absolute value of `number`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> abs(-3.33)
3.33
iex> abs(-3)
3
"""
@doc guard: true
@spec abs(number) :: number
def abs(number) do
:erlang.abs(number)
end
@doc """
Invokes the given anonymous function `fun` with the list of
arguments `args`.
If the number of arguments is known at compile time, prefer
`fun.(arg_1, arg_2, ..., arg_n)` as it is clearer than
`apply(fun, [arg_1, arg_2, ..., arg_n])`.
Inlined by the compiler.
## Examples
iex> apply(fn x -> x * 2 end, [2])
4
"""
@spec apply(fun, [any]) :: any
def apply(fun, args) do
:erlang.apply(fun, args)
end
@doc """
Invokes the given function from `module` with the list of
arguments `args`.
`apply/3` is used to invoke functions where the module, function
name or arguments are defined dynamically at runtime. For this
reason, you can't invoke macros using `apply/3`, only functions.
If the number of arguments and the function name are known at compile time,
prefer `module.function(arg_1, arg_2, ..., arg_n)` as it is clearer than
`apply(module, :function, [arg_1, arg_2, ..., arg_n])`.
`apply/3` cannot be used to call private functions.
Inlined by the compiler.
## Examples
iex> apply(Enum, :reverse, [[1, 2, 3]])
[3, 2, 1]
"""
@spec apply(module, function_name :: atom, [any]) :: any
def apply(module, function_name, args) do
:erlang.apply(module, function_name, args)
end
@doc """
Extracts the part of the binary at `start` with `size`.
If `start` or `size` reference in any way outside the binary,
an `ArgumentError` exception is raised.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> binary_part("foo", 1, 2)
"oo"
A negative `size` can be used to extract bytes that come *before* the byte
at `start`:
iex> binary_part("Hello", 5, -3)
"llo"
An `ArgumentError` is raised when the `size` is outside of the binary:
binary_part("Hello", 0, 10)
** (ArgumentError) argument error
"""
@doc guard: true
@spec binary_part(binary, non_neg_integer, integer) :: binary
def binary_part(binary, start, size) do
:erlang.binary_part(binary, start, size)
end
@doc """
Returns an integer which is the size in bits of `bitstring`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> bit_size(<<433::16, 3::3>>)
19
iex> bit_size(<<1, 2, 3>>)
24
"""
@doc guard: true
@spec bit_size(bitstring) :: non_neg_integer
def bit_size(bitstring) do
:erlang.bit_size(bitstring)
end
@doc """
Returns the number of bytes needed to contain `bitstring`.
That is, if the number of bits in `bitstring` is not divisible by 8, the
resulting number of bytes will be rounded up (by excess). This operation
happens in constant time.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> byte_size(<<433::16, 3::3>>)
3
iex> byte_size(<<1, 2, 3>>)
3
"""
@doc guard: true
@spec byte_size(bitstring) :: non_neg_integer
def byte_size(bitstring) do
:erlang.byte_size(bitstring)
end
@doc """
Returns the smallest integer greater than or equal to `number`.
If you want to perform ceil operation on other decimal places,
use `Float.ceil/2` instead.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> ceil(10)
10
iex> ceil(10.1)
11
iex> ceil(-10.1)
-10
"""
@doc since: "1.8.0", guard: true
@spec ceil(number) :: integer
def ceil(number) do
:erlang.ceil(number)
end
@doc """
Performs an integer division.
Raises an `ArithmeticError` exception if one of the arguments is not an
integer, or when the `divisor` is `0`.
`div/2` performs *truncated* integer division. This means that
the result is always rounded towards zero.
If you want to perform floored integer division (rounding towards negative infinity),
use `Integer.floor_div/2` instead.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> div(5, 2)
2
iex> div(6, -4)
-1
iex> div(-99, 2)
-49
div(100, 0)
** (ArithmeticError) bad argument in arithmetic expression
"""
@doc guard: true
@spec div(integer, neg_integer | pos_integer) :: integer
def div(dividend, divisor) do
:erlang.div(dividend, divisor)
end
@doc """
Stops the execution of the calling process with the given reason.
Since evaluating this function causes the process to terminate,
it has no return value.
Inlined by the compiler.
## Examples
When a process reaches its end, by default it exits with
reason `:normal`. You can also call `exit/1` explicitly if you
want to terminate a process but not signal any failure:
exit(:normal)
In case something goes wrong, you can also use `exit/1` with
a different reason:
exit(:seems_bad)
If the exit reason is not `:normal`, all the processes linked to the process
that exited will crash (unless they are trapping exits).
## OTP exits
Exits are used by the OTP to determine if a process exited abnormally
or not. The following exits are considered "normal":
* `exit(:normal)`
* `exit(:shutdown)`
* `exit({:shutdown, term})`
Exiting with any other reason is considered abnormal and treated
as a crash. This means the default supervisor behavior kicks in,
error reports are emitted, and so forth.
This behavior is relied on in many different places. For example,
`ExUnit` uses `exit(:shutdown)` when exiting the test process to
signal linked processes, supervision trees and so on to politely
shut down too.
## CLI exits
Building on top of the exit signals mentioned above, if the
process started by the command line exits with any of the three
reasons above, its exit is considered normal and the Operating
System process will exit with status 0.
It is, however, possible to customize the operating system exit
signal by invoking:
exit({:shutdown, integer})
This will cause the operating system process to exit with the status given by
`integer` while signaling all linked Erlang processes to politely
shut down.
Any other exit reason will cause the operating system process to exit with
status `1` and linked Erlang processes to crash.
"""
@spec exit(term) :: no_return
def exit(reason) do
:erlang.exit(reason)
end
@doc """
Returns the largest integer smaller than or equal to `number`.
If you want to perform floor operation on other decimal places,
use `Float.floor/2` instead.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> floor(10)
10
iex> floor(9.7)
9
iex> floor(-9.7)
-10
"""
@doc since: "1.8.0", guard: true
@spec floor(number) :: integer
def floor(number) do
:erlang.floor(number)
end
@doc """
Returns the head of a list. Raises `ArgumentError` if the list is empty.
The head of a list is its first element.
It works with improper lists.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> hd([1, 2, 3, 4])
1
iex> hd([1 | 2])
1
Giving it an empty list raises:
hd([])
** (ArgumentError) argument error
"""
@doc guard: true
@spec hd(nonempty_maybe_improper_list(elem, term)) :: elem when elem: term
def hd(list) do
:erlang.hd(list)
end
@doc """
Returns `true` if `term` is an atom, otherwise returns `false`.
Note `true`, `false`, and `nil` are atoms in Elixir, as well as
module names. Therefore this function will return `true` to all
of those values.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_atom(:name)
true
iex> is_atom(false)
true
iex> is_atom(AnAtom)
true
iex> is_atom("string")
false
"""
@doc guard: true
@spec is_atom(term) :: boolean
def is_atom(term) do
:erlang.is_atom(term)
end
@doc """
Returns `true` if `term` is a binary, otherwise returns `false`.
A binary always contains a complete number of bytes.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_binary("foo")
true
iex> is_binary(<<1::3>>)
false
"""
@doc guard: true
@spec is_binary(term) :: boolean
def is_binary(term) do
:erlang.is_binary(term)
end
@doc """
Returns `true` if `term` is a bitstring (including a binary), otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_bitstring("foo")
true
iex> is_bitstring(<<1::3>>)
true
"""
@doc guard: true
@spec is_bitstring(term) :: boolean
def is_bitstring(term) do
:erlang.is_bitstring(term)
end
@doc """
Returns `true` if `term` is either the atom `true` or the atom `false` (i.e.,
a boolean), otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_boolean(false)
true
iex> is_boolean(true)
true
iex> is_boolean(:test)
false
"""
@doc guard: true
@spec is_boolean(term) :: boolean
def is_boolean(term) do
:erlang.is_boolean(term)
end
@doc """
Returns `true` if `term` is a floating-point number, otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_float(2.15)
true
iex> is_float(3.45e5)
true
iex> is_float(5)
false
"""
@doc guard: true
@spec is_float(term) :: boolean
def is_float(term) do
:erlang.is_float(term)
end
@doc """
Returns `true` if `term` is a function, otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_function(fn x -> x + x end)
true
iex> is_function("not a function")
false
"""
@doc guard: true
@spec is_function(term) :: boolean
def is_function(term) do
:erlang.is_function(term)
end
@doc """
Returns `true` if `term` is a function that can be applied with `arity` number of arguments;
otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_function(fn x -> x * 2 end, 1)
true
iex> is_function(fn x -> x * 2 end, 2)
false
"""
@doc guard: true
@spec is_function(term, non_neg_integer) :: boolean
def is_function(term, arity) do
:erlang.is_function(term, arity)
end
@doc """
Returns `true` if `term` is an integer, otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_integer(5)
true
iex> is_integer(5.0)
false
"""
@doc guard: true
@spec is_integer(term) :: boolean
def is_integer(term) do
:erlang.is_integer(term)
end
@doc """
Returns `true` if `term` is a list with zero or more elements, otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_list([1, 2, 3])
true
iex> is_list(key: :sum, value: 3)
true
iex> is_list({1, 2, 3})
false
"""
@doc guard: true
@spec is_list(term) :: boolean
def is_list(term) do
:erlang.is_list(term)
end
@doc """
Returns `true` if `term` is either an integer or a floating-point number;
otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_number(2.15)
true
iex> is_number(5)
true
iex> is_number(:one)
false
"""
@doc guard: true
@spec is_number(term) :: boolean
def is_number(term) do
:erlang.is_number(term)
end
@doc """
Returns `true` if `term` is a PID (process identifier), otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> {:ok, agent_pid} = Agent.start_link(fn -> 0 end)
iex> is_pid(agent_pid)
true
iex> is_pid(self())
true
iex> is_pid(:pid)
false
"""
@doc guard: true
@spec is_pid(term) :: boolean
def is_pid(term) do
:erlang.is_pid(term)
end
@doc """
Returns `true` if `term` is a port identifier, otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> [port | _] = Port.list()
iex> is_port(port)
true
iex> is_port(:port)
false
"""
@doc guard: true
@spec is_port(term) :: boolean
def is_port(term) do
:erlang.is_port(term)
end
@doc """
Returns `true` if `term` is a reference, otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> ref = make_ref()
iex> is_reference(ref)
true
iex> is_reference(:ref)
false
"""
@doc guard: true
@spec is_reference(term) :: boolean
def is_reference(term) do
:erlang.is_reference(term)
end
@doc """
Returns `true` if `term` is a tuple, otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_tuple({1, 2, 3})
true
iex> is_tuple({})
true
iex> is_tuple(true)
false
"""
@doc guard: true
@spec is_tuple(term) :: boolean
def is_tuple(term) do
:erlang.is_tuple(term)
end
@doc """
Returns `true` if `term` is a map, otherwise returns `false`.
Allowed in guard tests. Inlined by the compiler.
> #### Structs are maps {: .info}
>
> Structs are also maps, and many of Elixir data structures are implemented
> using structs: `Range`s, `Regex`es, `Date`s...
>
> iex> is_map(1..10)
> true
> iex> is_map(~D[2024-04-18])
> true
>
> If you mean to specifically check for non-struct maps, use
> `is_non_struct_map/1` instead.
>
> iex> is_non_struct_map(1..10)
> false
"""
@doc guard: true
@spec is_map(term) :: boolean
def is_map(term) do
:erlang.is_map(term)
end
@doc """
Returns `true` if `key` is a key in `map`, otherwise returns `false`.
It raises `BadMapError` if the first element is not a map.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> is_map_key(%{a: "foo", b: "bar"}, :a)
true
iex> is_map_key(%{a: "foo", b: "bar"}, :c)
false
"""
@doc guard: true, since: "1.10.0"
@spec is_map_key(map, term) :: boolean
def is_map_key(map, key) do
:erlang.is_map_key(key, map)
end
@doc """
Returns the length of `list`.
Allowed in guard tests. Inlined by the compiler.
## Examples
iex> length([1, 2, 3, 4, 5, 6, 7, 8, 9])