Monthly Downloads: 28
Programming language: Elixir
License: MIT License
Tags: Macros    
Latest version: v0.5.1

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Macros expanding into code that can be safely used in guard clauses.


Update your mix.exs file and run mix deps.get.

defp deps do
  [{:guardsafe, "~> 0.5.0"}]

Import all the macros...

defmodule MyModule do
  import Guardsafe

...or just the ones you need.

defmodule MyOtherModule do
  import Guardsafe, only: [divisible_by?: 2, integer?: 1]

Now go forth and make your guard clauses more readable!

def leap_year?(year) when not integer?(year), do: raise "That's not a proper year!"
def leap_year?(year) when divisible_by?(year, 400), do: true
def leap_year?(year) when divisible_by?(year, 100), do: false
def leap_year?(year), do: divisible_by?(year, 4)

Documentation for each macro is of course available in iex.

iex(1)> h Guardsafe.divisible_by?

                    defmacro divisible_by?(number, divisor)

Expands divisible_by?(number, divisor) into rem(number, divisor) == 0

Available macros

NB: If a macro is translated into a function residing in another module than Kernel you need to require it before use, e.g. require Integer.

Macros for checking types

  • atom?/1 - translates into Kernel.is_atom/1
  • binary?/1 - translates into Kernel.is_binary/1
  • bitstring?/1 - translates into Kernel.is_bitstring/1
  • boolean?/1 - translates into Kernel.is_boolean/1
  • float?/1 - translates into Kernel.is_float/1
  • function?/1 - translates into Kernel.is_function/1
  • function?/2 - translates into Kernel.is_function/2
  • integer?/1 - translates into Kernel.is_integer/1
  • list?/1 - translates into Kernel.is_list/1
  • map?/1 - translates into Kernel.is_map/1
  • nil?/1 - translates into Kernel.is_nil/1
  • number?/1 - translates into Kernel.is_number/1
  • pid?/1 - translates into Kernel.is_pid/1
  • port?/1 - translates into Kernel.is_port/1
  • reference?/1 - translates into Kernel.is_reference/1
  • tuple?/1 - translates into Kernel.is_tuple/1

Macros for checking values

  • divisible_by?/2 - checks whether two integers are evenly divisible.
  • even?/1 - returns true for even integers.
  • odd?/1 - returns true for odd integers.
  • within?/3 - checks whether a value is in the range of the last two arguments.

Macros for dates and times

  • date?/1 - checks if the term is an Erlang-style date tuple.
  • datetime?/1 - checks if the term is an Erlang-style datetime tuple.
  • time?/1 - checks if the term is an Erlang-style time tuple.

These can come in handy when working with a library such as GoodTimes.

Why nil? and float? instead of is_nil and is_float

While the Elixir core team thinks that nil? compared to is_nil is an inconcistency, others, especially Rubyists, might be more comfortable with the nil? notation. Honestly though, this is mostly intended as a display of how Elixir's metaprogramming capabilities can be used to shape the look and feel of the language itself.

Online documentation

For more information, see the full documentation.


  1. Fork this repository
  2. Create your feature branch (git checkout -b quis-custodiet-ipsos-custodes)
  3. Commit your changes (git commit -am 'Guards! Guards!')
  4. Push to the branch (git push origin quis-custodiet-ipsos-custodes)
  5. Create a new Pull Request