View Source Macro (Elixir v1.15.0-dev)

Functions for manipulating AST and implementing macros.

Macros are compile-time constructs that receive Elixir's AST as input and return Elixir's AST as output.

Many of the functions in this module exist precisely to work with Elixir AST, to traverse, query, and transform it.

Let's see a simple example that shows the difference between functions and macros:

defmodule Example do
  defmacro macro_inspect(value) do
    IO.inspect(value)
    value
  end

  def fun_inspect(value) do
    IO.inspect(value)
    value
  end
end

Now let's give it a try:

import Example

macro_inspect(1)
#=> 1
#=> 1

fun_inspect(1)
#=> 1
#=> 1

So far they behave the same, as we are passing an integer as argument. But let's see what happens when we pass an expression:

macro_inspect(1 + 2)
#=> {:+, [line: 3], [1, 2]}
#=> 3

fun_inspect(1 + 2)
#=> 3
#=> 3

The macro receives the representation of the code given as argument, while a function receives the result of the code given as argument. A macro must return a superset of the code representation. See input/0 and output/0 for more information.

To learn more about Elixir's AST and how to build them programmatically, see quote/2.

Note: the functions in this module do not evaluate code. In fact, evaluating code from macros is often an anti-pattern. For code evaluation, see the Code module.

custom-sigils

Custom Sigils

Macros are also commonly used to implement custom sigils. To create a custom sigil, define a macro with the name sigil_{identifier} that takes two arguments. The first argument will be the string, the second will be a charlist containing any modifiers. If the sigil is lower case (such as sigil_x) then the string argument will allow interpolation. If the sigil is upper case (such as sigil_X) then the string will not be interpolated.

Valid modifiers include only lower and upper case letters. Other characters will cause a syntax error.

The module containing the custom sigil must be imported before the sigil syntax can be used.

examples

Examples

defmodule MySigils do
  defmacro sigil_x(term, [?r]) do
    quote do
      unquote(term) |> String.reverse()
    end
  end
  defmacro sigil_x(term, _modifiers) do
    term
  end
  defmacro sigil_X(term, [?r]) do
    quote do
      unquote(term) |> String.reverse()
    end
  end
  defmacro sigil_X(term, _modifiers) do
    term
  end
end

import MySigils

~x(with #{"inter" <> "polation"})
#=>"with interpolation"

~x(with #{"inter" <> "polation"})r
#=>"noitalopretni htiw"

~X(without #{"interpolation"})
#=>"without \#{"interpolation"}"

~X(without #{"interpolation"})r
#=>"}\"noitalopretni\"{# tuohtiw"

Link to this section Summary

Types

A captured remote function in the format of &Mod.fun/arity

The inputs of a macro

A keyword list of AST metadata.

The output of a macro

t()

Abstract Syntax Tree (AST)

Functions

Converts the given string to CamelCase format.

Classifies a runtime atom based on its possible AST placement.

Default backend for Kernel.dbg/2.

Decomposes a local or remote call into its remote part (when provided), function name and argument list.

Recursively escapes a value so it can be inserted into a syntax tree.

Receives an AST node and expands it until it can no longer be expanded.

Expands all literals in ast with the given env.

Expands all literals in ast with the given acc and fun.

Receives an AST node and expands it once.

Generates AST nodes for a given number of required argument variables using Macro.var/2.

Generates AST nodes for a given number of required argument variables using Macro.unique_var/2.

Inspects atom according to different source formats.

Returns true if the given name and arity is an operator.

Returns the path to the node in ast which fun returns true.

Pipes expr into the call_args at the given position.

This function behaves like prewalk/2, but performs a depth-first, post-order traversal of quoted expressions.

This functions behaves like prewalk/3, but performs a depth-first, post-order traversal of quoted expressions using an accumulator.

Returns an enumerable that traverses the ast in depth-first, post-order traversal.

Performs a depth-first, pre-order traversal of quoted expressions.

Performs a depth-first, pre-order traversal of quoted expressions using an accumulator.

Returns an enumerable that traverses the ast in depth-first, pre-order traversal.

Returns true if the given quoted expression represents a quoted literal.

Returns true if the given name and arity is a special form.

Expands the struct given by module in the given env.

Converts the given expression AST to a string.

Converts the given expression AST to a string.

Performs a depth-first traversal of quoted expressions using an accumulator.

Converts the given argument to a string with the underscore-slash format.

Unescapes characters in a string.

Unescapes characters in a string according to the given mapping.

Generates an AST node representing a unique variable given by the atoms var and context.

Breaks a pipeline expression into a list.

Applies the given function to the node metadata if it contains one.

Validates the given expressions are valid quoted expressions.

Generates an AST node representing the variable given by the atoms var and context.

Link to this section Types

Link to this type

captured_remote_function()

View Source
@type captured_remote_function() :: (... -> any())

A captured remote function in the format of &Mod.fun/arity

@type input() ::
  input_expr() | {input(), input()} | [input()] | atom() | number() | binary()

The inputs of a macro

@type metadata() :: keyword()

A keyword list of AST metadata.

The metadata in Elixir AST is a keyword list of values. Any key can be used and different parts of the compiler may use different keys. For example, the AST received by a macro will always include the :line annotation, while the AST emitted by quote/2 will only have the :line annotation if the :line option is provided.

The following metadata keys are public:

  • :context - Defines the context in which the AST was generated. For example, quote/2 will include the module calling quote/2 as the context. This is often used to distinguish regular code from code generated by a macro or by quote/2.
  • :counter - The variable counter used for variable hygiene. In terms of the compiler, each variable is identified by the combination of either name and metadata[:counter], or name and context.
  • :generated - Whether the code should be considered as generated by the compiler or not. This means the compiler and tools like Dialyzer may not emit certain warnings.
  • :if_undefined - How to expand a variable that is undefined. Set it to :apply if you want a variable to become a nullary call without warning or :raise
  • :keep - Used by quote/2 with the option location: :keep to annotate the file and the line number of the quoted source.
  • :line - The line number of the AST node.

The following metadata keys are enabled by Code.string_to_quoted/2:

  • :closing - contains metadata about the closing pair, such as a } in a tuple or in a map, or such as the closing ) in a function call with parens. The :closing does not delimit the end of expression if there are :do and :end metadata (when :token_metadata is true)
  • :column - the column number of the AST node (when :columns is true)
  • :delimiter - contains the opening delimiter for sigils, strings, and charlists as a string (such as "{", "/", "'", and the like)
  • :format - set to :keyword when an atom is defined as a keyword
  • :do - contains metadata about the do location in a function call with do-end blocks (when :token_metadata is true)
  • :end - contains metadata about the end location in a function call with do-end blocks (when :token_metadata is true)
  • :end_of_expression - denotes when the end of expression effectively happens. Available for all expressions except the last one inside a __block__ (when :token_metadata is true)
  • :indentation - indentation of a sigil heredoc

The following metadata keys are private:

  • :alias - Used for alias hygiene.
  • :ambiguous_op - Used for improved error messages in the compiler.
  • :imports - Used for import hygiene.
  • :var - Used for improved error messages on undefined variables.

Do not rely on them as they may change or be fully removed in future versions of the language. They are often used by quote/2 and the compiler to provide features like hygiene, better error messages, and so forth.

If you introduce custom keys into the AST metadata, please make sure to prefix them with the name of your library or application, so that they will not conflict with keys that could potentially be introduced by the compiler in the future.

@type output() ::
  output_expr()
  | {output(), output()}
  | [output()]
  | atom()
  | number()
  | binary()
  | captured_remote_function()
  | pid()

The output of a macro

@type t() :: input()

Abstract Syntax Tree (AST)

Link to this section Functions

@spec camelize(String.t()) :: String.t()

Converts the given string to CamelCase format.

This function was designed to camelize language identifiers/tokens, that's why it belongs to the Macro module. Do not use it as a general mechanism for camelizing strings as it does not support Unicode or characters that are not valid in Elixir identifiers.

examples

Examples

iex> Macro.camelize("foo_bar")
"FooBar"

iex> Macro.camelize("foo/bar")
"Foo.Bar"

If uppercase characters are present, they are not modified in any way as a mechanism to preserve acronyms:

iex> Macro.camelize("API.V1")
"API.V1"
iex> Macro.camelize("API_SPEC")
"API_SPEC"
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classify_atom(atom)

View Source (since 1.14.0)
@spec classify_atom(atom()) :: :alias | :identifier | :quoted | :unquoted

Classifies a runtime atom based on its possible AST placement.

It returns one of the following atoms:

  • :alias - the atom represents an alias

  • :identifier - the atom can be used as a variable or local function call (as well as be an unquoted atom)

  • :unquoted - the atom can be used in its unquoted form, includes operators and atoms with @ in them

  • :quoted - all other atoms which can only be used in their quoted form

Most operators are going to be :unquoted, such as :+, with some exceptions returning :quoted due to ambiguity, such as :"::". Use operator?/2 to check if a given atom is an operator.

examples

Examples

iex> Macro.classify_atom(:foo)
:identifier
iex> Macro.classify_atom(Foo)
:alias
iex> Macro.classify_atom(:foo@bar)
:unquoted
iex> Macro.classify_atom(:+)
:unquoted
iex> Macro.classify_atom(:Foo)
:unquoted
iex> Macro.classify_atom(:"with spaces")
:quoted
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dbg(code, options, env)

View Source (since 1.14.0)
@spec dbg(t(), t(), Macro.Env.t()) :: t()

Default backend for Kernel.dbg/2.

This function provides a default backend for Kernel.dbg/2. See the Kernel.dbg/2 documentation for more information.

This function:

  • prints information about the given env
  • prints information about code and its returned value (using opts to inspect terms)
  • returns the value returned by evaluating code

You can call this function directly to build Kernel.dbg/2 backends that fall back to this function.

This function raises if the context of the given env is :match or :guard.

@spec decompose_call(t()) :: {atom(), [t()]} | {t(), atom(), [t()]} | :error

Decomposes a local or remote call into its remote part (when provided), function name and argument list.

Returns :error when an invalid call syntax is provided.

examples

Examples

iex> Macro.decompose_call(quote(do: foo))
{:foo, []}

iex> Macro.decompose_call(quote(do: foo()))
{:foo, []}

iex> Macro.decompose_call(quote(do: foo(1, 2, 3)))
{:foo, [1, 2, 3]}

iex> Macro.decompose_call(quote(do: Elixir.M.foo(1, 2, 3)))
{{:__aliases__, [], [:Elixir, :M]}, :foo, [1, 2, 3]}

iex> Macro.decompose_call(quote(do: 42))
:error

iex> Macro.decompose_call(quote(do: {:foo, [], []}))
:error
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escape(expr, opts \\ [])

View Source
@spec escape(
  term(),
  keyword()
) :: t()

Recursively escapes a value so it can be inserted into a syntax tree.

examples

Examples

iex> Macro.escape(:foo)
:foo

iex> Macro.escape({:a, :b, :c})
{:{}, [], [:a, :b, :c]}

iex> Macro.escape({:unquote, [], [1]}, unquote: true)
1

options

Options

  • :unquote - when true, this function leaves unquote/1 and unquote_splicing/1 statements unescaped, effectively unquoting the contents on escape. This option is useful only when escaping ASTs which may have quoted fragments in them. Defaults to false.

  • :prune_metadata - when true, removes metadata from escaped AST nodes. Note this option changes the semantics of escaped code and it should only be used when escaping ASTs. Defaults to false.

    As an example, ExUnit stores the AST of every assertion, so when an assertion fails we can show code snippets to users. Without this option, each time the test module is compiled, we get a different MD5 of the module bytecode, because the AST contains metadata, such as counters, specific to the compilation environment. By pruning the metadata, we ensure that the module is deterministic and reduce the amount of data ExUnit needs to keep around. Only the minimal amount of metadata is kept, such as :line and :no_parens.

comparison-to-quote-2

Comparison to quote/2

The escape/2 function is sometimes confused with quote/2, because the above examples behave the same with both. The key difference is best illustrated when the value to escape is stored in a variable.

iex> Macro.escape({:a, :b, :c})
{:{}, [], [:a, :b, :c]}
iex> quote do: {:a, :b, :c}
{:{}, [], [:a, :b, :c]}

iex> value = {:a, :b, :c}
iex> Macro.escape(value)
{:{}, [], [:a, :b, :c]}

iex> quote do: value
{:value, [], __MODULE__}

iex> value = {:a, :b, :c}
iex> quote do: unquote(value)
{:a, :b, :c}

escape/2 is used to escape values (either directly passed or variable bound), while quote/2 produces syntax trees for expressions.

@spec expand(t(), Macro.Env.t()) :: t()

Receives an AST node and expands it until it can no longer be expanded.

Note this function does not traverse the AST, only the root node is expanded.

This function uses expand_once/2 under the hood. Check it out for more information and examples.

Link to this function

expand_literals(ast, env)

View Source (since 1.14.1)
@spec expand_literals(t(), Macro.Env.t()) :: t()

Expands all literals in ast with the given env.

This function is mostly used to remove compile-time dependencies from AST nodes. In such cases, the given environment is usually manipulated to represent a function:

Macro.expand_literals(ast, %{env | function: {:my_code, 1}})

At the moment, the only expandable literal nodes in an AST are aliases, so this function only expands aliases.

However, be careful when removing compile-time dependencies between modules. If you remove them but you still invoke the module at compile-time, Elixir will be unable to properly recompile modules when they change.

Link to this function

expand_literals(ast, acc, fun)

View Source (since 1.14.1)
@spec expand_literals(t(), acc, (t(), acc -> {t(), acc})) :: t() when acc: term()

Expands all literals in ast with the given acc and fun.

fun will be invoked with an expandable AST node and acc and must return a new node with acc. This is a general version of expand_literals/2 which supports a custom expansion function. Please check expand_literals/2 for use cases and pitfalls.

@spec expand_once(t(), Macro.Env.t()) :: t()

Receives an AST node and expands it once.

The following contents are expanded:

If the expression cannot be expanded, it returns the expression itself. This function does not traverse the AST, only the root node is expanded.

expand_once/2 performs the expansion just once. Check expand/2 to perform expansion until the node can no longer be expanded.

examples

Examples

In the example below, we have a macro that generates a module with a function named name_length that returns the length of the module name. The value of this function will be calculated at compilation time and not at runtime.

Consider the implementation below:

defmacro defmodule_with_length(name, do: block) do
  length = length(Atom.to_charlist(name))

  quote do
    defmodule unquote(name) do
      def name_length, do: unquote(length)
      unquote(block)
    end
  end
end

When invoked like this:

defmodule_with_length My.Module do
  def other_function, do: ...
end

The compilation will fail because My.Module when quoted is not an atom, but a syntax tree as follows:

{:__aliases__, [], [:My, :Module]}

That said, we need to expand the aliases node above to an atom, so we can retrieve its length. Expanding the node is not straightforward because we also need to expand the caller aliases. For example:

alias MyHelpers, as: My

defmodule_with_length My.Module do
  def other_function, do: ...
end

The final module name will be MyHelpers.Module and not My.Module. With Macro.expand/2, such aliases are taken into consideration. Local and remote macros are also expanded. We could rewrite our macro above to use this function as:

defmacro defmodule_with_length(name, do: block) do
  expanded = Macro.expand(name, __CALLER__)
  length = length(Atom.to_charlist(expanded))

  quote do
    defmodule unquote(name) do
      def name_length, do: unquote(length)
      unquote(block)
    end
  end
end
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generate_arguments(amount, context)

View Source (since 1.5.0)
@spec generate_arguments(0, context :: atom()) :: []
@spec generate_arguments(pos_integer(), context) :: [{atom(), [], context}, ...]
when context: atom()

Generates AST nodes for a given number of required argument variables using Macro.var/2.

Note the arguments are not unique. If you later on want to access the same variables, you can invoke this function with the same inputs. Use generate_unique_arguments/2 to generate a unique arguments that can't be overridden.

examples

Examples

iex> Macro.generate_arguments(2, __MODULE__)
[{:arg1, [], __MODULE__}, {:arg2, [], __MODULE__}]
Link to this function

generate_unique_arguments(amount, context)

View Source (since 1.11.3)
@spec generate_unique_arguments(0, context :: atom()) :: []
@spec generate_unique_arguments(pos_integer(), context) :: [
  {atom(), [{:counter, integer()}], context},
  ...
]
when context: atom()

Generates AST nodes for a given number of required argument variables using Macro.unique_var/2.

examples

Examples

iex> [var1, var2] = Macro.generate_unique_arguments(2, __MODULE__)
iex> {:arg1, [counter: c1], __MODULE__} = var1
iex> {:arg2, [counter: c2], __MODULE__} = var2
iex> is_integer(c1) and is_integer(c2)
true
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inspect_atom(source_format, atom)

View Source (since 1.14.0)
@spec inspect_atom(:literal | :key | :remote_call, atom()) :: binary()

Inspects atom according to different source formats.

The atom can be inspected according to the three different formats it appears in the AST: as a literal (:literal), as a key (:key), or as the function name of a remote call (:remote_call).

examples

Examples

as-a-literal

As a literal

Literals include regular atoms, quoted atoms, operators, aliases, and the special nil, true, and false atoms.

iex> Macro.inspect_atom(:literal, nil)
"nil"
iex> Macro.inspect_atom(:literal, :foo)
":foo"
iex> Macro.inspect_atom(:literal, :<>)
":<>"
iex> Macro.inspect_atom(:literal, :Foo)
":Foo"
iex> Macro.inspect_atom(:literal, Foo.Bar)
"Foo.Bar"
iex> Macro.inspect_atom(:literal, :"with spaces")
":\"with spaces\""

as-a-key

As a key

Inspect an atom as a key of a keyword list or a map.

iex> Macro.inspect_atom(:key, :foo)
"foo:"
iex> Macro.inspect_atom(:key, :<>)
"<>:"
iex> Macro.inspect_atom(:key, :Foo)
"Foo:"
iex> Macro.inspect_atom(:key, :"with spaces")
"\"with spaces\":"

as-a-remote-call

As a remote call

Inspect an atom the function name of a remote call.

iex> Macro.inspect_atom(:remote_call, :foo)
"foo"
iex> Macro.inspect_atom(:remote_call, :<>)
"<>"
iex> Macro.inspect_atom(:remote_call, :Foo)
"\"Foo\""
iex> Macro.inspect_atom(:remote_call, :"with spaces")
"\"with spaces\""
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operator?(name, arity)

View Source (since 1.7.0)
@spec operator?(name :: atom(), arity()) :: boolean()

Returns true if the given name and arity is an operator.

examples

Examples

iex> Macro.operator?(:not_an_operator, 3)
false
iex> Macro.operator?(:.., 0)
true
iex> Macro.operator?(:+, 1)
true
iex> Macro.operator?(:++, 2)
true
iex> Macro.operator?(:..//, 3)
true
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path(ast, fun)

View Source (since 1.14.0)

Returns the path to the node in ast which fun returns true.

The path is a list, starting with the node in which fun returns true, followed by all of its parents.

Computing the path can be an efficient operation when you want to find a particular node in the AST within its context and then assert something about it.

examples

Examples

iex> Macro.path(quote(do: [1, 2, 3]), & &1 == 3)
[3, [1, 2, 3]]

iex> Macro.path(quote(do: Foo.bar(3)), & &1 == 3)
[3, quote(do: Foo.bar(3))]

iex> Macro.path(quote(do: %{foo: [bar: :baz]}), & &1 == :baz)
[
  :baz,
  {:bar, :baz},
  [bar: :baz],
  {:foo, [bar: :baz]},
  {:%{}, [], [foo: [bar: :baz]]}
]
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pipe(expr, call_args, position)

View Source
@spec pipe(t(), t(), integer()) :: t()

Pipes expr into the call_args at the given position.

This function can be used to implement |> like functionality. For example, |> itself is implemented as:

defmacro left |> right do
  Macro.pipe(left, right, 0)
end

expr is the AST of an expression. call_args must be the AST of a call, otherwise this function will raise an error. As an example, consider the pipe operator |>/2, which uses this function to build pipelines.

Even if the expression is piped into the AST, it doesn't necessarily mean that the AST is valid. For example, you could pipe an argument to div/2, effectively turning it into a call to div/3, which is a function that doesn't exist by default. The code will raise unless a div/3 function is locally defined.

@spec postwalk(t(), (t() -> t())) :: t()

This function behaves like prewalk/2, but performs a depth-first, post-order traversal of quoted expressions.

@spec postwalk(t(), any(), (t(), any() -> {t(), any()})) :: {t(), any()}

This functions behaves like prewalk/3, but performs a depth-first, post-order traversal of quoted expressions using an accumulator.

Link to this function

postwalker(ast)

View Source (since 1.13.0)
@spec postwalker(t()) :: Enumerable.t()

Returns an enumerable that traverses the ast in depth-first, post-order traversal.

examples

Examples

iex> ast = quote do: foo(1, "abc")
iex> Enum.map(Macro.postwalker(ast), & &1)
[1, "abc", {:foo, [], [1, "abc"]}]
@spec prewalk(t(), (t() -> t())) :: t()

Performs a depth-first, pre-order traversal of quoted expressions.

Returns a new AST where each node is the result of invoking fun on each corresponding node of ast.

examples

Examples

iex> ast = quote do: 5 + 3 * 7
iex> {:+, _, [5, {:*, _, [3, 7]}]} = ast
iex> new_ast = Macro.prewalk(ast, fn
...>   {:+, meta, children} -> {:*, meta, children}
...>   {:*, meta, children} -> {:+, meta, children}
...>   other -> other
...> end)
iex> {:*, _, [5, {:+, _, [3, 7]}]} = new_ast
iex> Code.eval_quoted(ast)
{26, []}
iex> Code.eval_quoted(new_ast)
{50, []}
@spec prewalk(t(), any(), (t(), any() -> {t(), any()})) :: {t(), any()}

Performs a depth-first, pre-order traversal of quoted expressions using an accumulator.

Returns a tuple where the first element is a new AST where each node is the result of invoking fun on each corresponding node and the second one is the final accumulator.

examples

Examples

iex> ast = quote do: 5 + 3 * 7
iex> {:+, _, [5, {:*, _, [3, 7]}]} = ast
iex> {new_ast, acc} = Macro.prewalk(ast, [], fn
...>   {:+, meta, children}, acc -> {{:*, meta, children}, [:+ | acc]}
...>   {:*, meta, children}, acc -> {{:+, meta, children}, [:* | acc]}
...>   other, acc -> {other, acc}
...> end)
iex> {{:*, _, [5, {:+, _, [3, 7]}]}, [:*, :+]} = {new_ast, acc}
iex> Code.eval_quoted(ast)
{26, []}
iex> Code.eval_quoted(new_ast)
{50, []}
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prewalker(ast)

View Source (since 1.13.0)
@spec prewalker(t()) :: Enumerable.t()

Returns an enumerable that traverses the ast in depth-first, pre-order traversal.

examples

Examples

iex> ast = quote do: foo(1, "abc")
iex> Enum.map(Macro.prewalker(ast), & &1)
[{:foo, [], [1, "abc"]}, 1, "abc"]
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quoted_literal?(term)

View Source (since 1.7.0)
@spec quoted_literal?(t()) :: boolean()

Returns true if the given quoted expression represents a quoted literal.

Atoms and numbers are always literals. Binaries, lists, tuples, maps, and structs are only literals if all of their terms are also literals.

examples

Examples

iex> Macro.quoted_literal?(quote(do: "foo"))
true
iex> Macro.quoted_literal?(quote(do: {"foo", 1}))
true
iex> Macro.quoted_literal?(quote(do: {"foo", 1, :baz}))
true
iex> Macro.quoted_literal?(quote(do: %{foo: "bar"}))
true
iex> Macro.quoted_literal?(quote(do: %URI{path: "/"}))
true
iex> Macro.quoted_literal?(quote(do: URI.parse("/")))
false
iex> Macro.quoted_literal?(quote(do: {foo, var}))
false
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special_form?(name, arity)

View Source (since 1.7.0)
@spec special_form?(name :: atom(), arity()) :: boolean()

Returns true if the given name and arity is a special form.

Link to this function

struct!(module, env)

View Source (since 1.8.0)
@spec struct!(module, Macro.Env.t()) :: %{
  :__struct__ => module,
  optional(atom()) => any()
}
when module: module()

Expands the struct given by module in the given env.

This is useful when a struct needs to be expanded at compilation time and the struct being expanded may or may not have been compiled. This function is also capable of expanding structs defined under the module being compiled.

It will raise CompileError if the struct is not available. From Elixir v1.12, calling this function also adds an export dependency on the given struct.

@spec to_string(t()) :: String.t()

Converts the given expression AST to a string.

This is a convenience function for converting AST into a string, which discards all formatting of the original code and wraps newlines around 98 characters. See Code.quoted_to_algebra/2 as a lower level function with more control around formatting.

examples

Examples

iex> Macro.to_string(quote(do: foo.bar(1, 2, 3)))
"foo.bar(1, 2, 3)"
This function is deprecated. Use Macro.to_string/1 instead.
@spec to_string(t(), (t(), String.t() -> String.t())) :: String.t()

Converts the given expression AST to a string.

The given fun is called for every node in the AST with two arguments: the AST of the node being printed and the string representation of that same node. The return value of this function is used as the final string representation for that AST node.

This function discards all formatting of the original code.

examples

Examples

Macro.to_string(quote(do: 1 + 2), fn
  1, _string -> "one"
  2, _string -> "two"
  _ast, string -> string
end)
#=> "one + two"
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traverse(ast, acc, pre, post)

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@spec traverse(t(), any(), (t(), any() -> {t(), any()}), (t(), any() -> {t(), any()})) ::
  {t(), any()}

Performs a depth-first traversal of quoted expressions using an accumulator.

Returns a tuple where the first element is a new AST and the second one is the final accumulator. The new AST is the result of invoking pre on each node of ast during the pre-order phase and post during the post-order phase.

examples

Examples

iex> ast = quote do: 5 + 3 * 7
iex> {:+, _, [5, {:*, _, [3, 7]}]} = ast
iex> {new_ast, acc} =
...>  Macro.traverse(
...>    ast,
...>    [],
...>    fn
...>      {:+, meta, children}, acc -> {{:-, meta, children}, [:- | acc]}
...>      {:*, meta, children}, acc -> {{:/, meta, children}, [:/ | acc]}
...>      other, acc -> {other, acc}
...>    end,
...>    fn
...>      {:-, meta, children}, acc -> {{:min, meta, children}, [:min | acc]}
...>      {:/, meta, children}, acc -> {{:max, meta, children}, [:max | acc]}
...>      other, acc -> {other, acc}
...>    end
...>  )
iex> {:min, _, [5, {:max, _, [3, 7]}]} = new_ast
iex> [:min, :max, :/, :-] = acc
iex> Code.eval_quoted(new_ast)
{5, []}
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underscore(atom_or_string)

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@spec underscore(module() | atom() | String.t()) :: String.t()

Converts the given argument to a string with the underscore-slash format.

The argument must either be an atom or a string. If an atom is given, it is assumed to be an Elixir module, so it is converted to a string and then processed.

This function was designed to format language identifiers/tokens with the underscore-slash format, that's why it belongs to the Macro module. Do not use it as a general mechanism for underscoring strings as it does not support Unicode or characters that are not valid in Elixir identifiers.

examples

Examples

iex> Macro.underscore("FooBar")
"foo_bar"

iex> Macro.underscore("Foo.Bar")
"foo/bar"

iex> Macro.underscore(Foo.Bar)
"foo/bar"

In general, underscore can be thought of as the reverse of camelize, however, in some cases formatting may be lost:

iex> Macro.underscore("SAPExample")
"sap_example"

iex> Macro.camelize("sap_example")
"SapExample"

iex> Macro.camelize("hello_10")
"Hello10"

iex> Macro.camelize("foo/bar")
"Foo.Bar"
@spec unescape_string(String.t()) :: String.t()

Unescapes characters in a string.

This is the unescaping behaviour used by default in Elixir single- and double-quoted strings. Check unescape_string/2 for information on how to customize the escaping map.

In this setup, Elixir will escape the following: \0, \a, \b, \d, \e, \f, \n, \r, \s, \t and \v. Bytes can be given as hexadecimals via \xNN and Unicode code points as \uNNNN escapes.

This function is commonly used on sigil implementations (like ~r, ~s and others), which receive a raw, unescaped string, and it can be used anywhere that needs to mimic how Elixir parses strings.

examples

Examples

iex> Macro.unescape_string("example\\n")
"example\n"

In the example above, we pass a string with \n escaped and return a version with it unescaped.

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unescape_string(string, map)

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@spec unescape_string(String.t(), (non_neg_integer() -> non_neg_integer() | false)) ::
  String.t()

Unescapes characters in a string according to the given mapping.

Check unescape_string/1 if you want to use the same mapping as Elixir single- and double-quoted strings.

mapping-function

Mapping function

The mapping function receives an integer representing the code point of the character it wants to unescape. There are also the special atoms :newline, :unicode, and :hex, which control newline, unicode, and escaping respectively.

Here is the default mapping function implemented by Elixir:

def unescape_map(:newline), do: true
def unescape_map(:unicode), do: true
def unescape_map(:hex), do: true
def unescape_map(?0), do: ?0
def unescape_map(?a), do: ?\a
def unescape_map(?b), do: ?\b
def unescape_map(?d), do: ?\d
def unescape_map(?e), do: ?\e
def unescape_map(?f), do: ?\f
def unescape_map(?n), do: ?\n
def unescape_map(?r), do: ?\r
def unescape_map(?s), do: ?\s
def unescape_map(?t), do: ?\t
def unescape_map(?v), do: ?\v
def unescape_map(e), do: e

If the unescape_map/1 function returns false, the char is not escaped and the backslash is kept in the string.

examples

Examples

Using the unescape_map/1 function defined above is easy:

Macro.unescape_string("example\\n", &unescape_map(&1))
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unique_var(var, context)

View Source (since 1.11.3)
@spec unique_var(var, context) :: {var, [{:counter, integer()}], context}
when var: atom(), context: atom()

Generates an AST node representing a unique variable given by the atoms var and context.

Calling this function with the same arguments will generate another variable, with its own unique counter. See var/2 for an alternative.

examples

Examples

iex> {:foo, [counter: c], __MODULE__} = Macro.unique_var(:foo, __MODULE__)
iex> is_integer(c)
true
@spec unpipe(t()) :: [t()]

Breaks a pipeline expression into a list.

The AST for a pipeline (a sequence of applications of |>/2) is similar to the AST of a sequence of binary operators or function applications: the top-level expression is the right-most :|> (which is the last one to be executed), and its left-hand and right-hand sides are its arguments:

quote do: 100 |> div(5) |> div(2)
#=> {:|>, _, [arg1, arg2]}

In the example above, the |>/2 pipe is the right-most pipe; arg1 is the AST for 100 |> div(5), and arg2 is the AST for div(2).

It's often useful to have the AST for such a pipeline as a list of function applications. This function does exactly that:

Macro.unpipe(quote do: 100 |> div(5) |> div(2))
#=> [{100, 0}, {{:div, [], [5]}, 0}, {{:div, [], [2]}, 0}]

We get a list that follows the pipeline directly: first the 100, then the div(5) (more precisely, its AST), then div(2). The 0 as the second element of the tuples is the position of the previous element in the pipeline inside the current function application: {{:div, [], [5]}, 0} means that the previous element (100) will be inserted as the 0th (first) argument to the div/2 function, so that the AST for that function will become {:div, [], [100, 5]} (div(100, 5)).

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update_meta(quoted, fun)

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@spec update_meta(t(), (keyword() -> keyword())) :: t()

Applies the given function to the node metadata if it contains one.

This is often useful when used with Macro.prewalk/2 to remove information like lines and hygienic counters from the expression for either storage or comparison.

examples

Examples

iex> quoted = quote line: 10, do: sample()
{:sample, [line: 10], []}
iex> Macro.update_meta(quoted, &Keyword.delete(&1, :line))
{:sample, [], []}
@spec validate(term()) :: :ok | {:error, term()}

Validates the given expressions are valid quoted expressions.

Check the type Macro.t/0 for a complete specification of a valid quoted expression.

It returns :ok if the expression is valid. Otherwise it returns a tuple in the form of {:error, remainder} where remainder is the invalid part of the quoted expression.

examples

Examples

iex> Macro.validate({:two_element, :tuple})
:ok
iex> Macro.validate({:three, :element, :tuple})
{:error, {:three, :element, :tuple}}

iex> Macro.validate([1, 2, 3])
:ok
iex> Macro.validate([1, 2, 3, {4}])
{:error, {4}}
@spec var(var, context) :: {var, [], context} when var: atom(), context: atom()

Generates an AST node representing the variable given by the atoms var and context.

Note this variable is not unique. If you later on want to access this same variable, you can invoke var/2 again with the same arguments. Use unique_var/2 to generate a unique variable that can't be overridden.

examples

Examples

In order to build a variable, a context is expected. Most of the times, in order to preserve hygiene, the context must be __MODULE__/0:

iex> Macro.var(:foo, __MODULE__)
{:foo, [], __MODULE__}

However, if there is a need to access the user variable, nil can be given:

iex> Macro.var(:foo, nil)
{:foo, [], nil}