EEx

v1.6.0

EEx

EEx v1.6.0 EEx View Source

EEx stands for Embedded Elixir. It allows you to embed Elixir code inside a string in a robust way.

iex> EEx.eval_string "foo <%= bar %>", [bar: "baz"]
"foo baz"

API

This module provides 3 main APIs for you to use:

  1. Evaluate a string (eval_string) or a file (eval_file) directly. This is the simplest API to use but also the slowest, since the code is evaluated and not compiled before.

  2. Define a function from a string (function_from_string) or a file (function_from_file). This allows you to embed the template as a function inside a module which will then be compiled. This is the preferred API if you have access to the template at compilation time.

  3. Compile a string (compile_string) or a file (compile_file) into Elixir syntax tree. This is the API used by both functions above and is available to you if you want to provide your own ways of handling the compiled template.

Options

All functions in this module accept EEx-related options. They are:

  • :line - the line to be used as the template start. Defaults to 1.
  • :file - the file to be used in the template. Defaults to the given file the template is read from or to “nofile” when compiling from a string.
  • :engine - the EEx engine to be used for compilation.
  • :trim - trims whitespace left/right of quotation tags

Engine

EEx has the concept of engines which allows you to modify or transform the code extracted from the given string or file.

By default, EEx uses the EEx.SmartEngine that provides some conveniences on top of the simple EEx.Engine.

Tags

EEx.SmartEngine supports the following tags:

<% Elixir expression - inline with output %>
<%= Elixir expression - replace with result %>
<%% EEx quotation - returns the contents inside %>
<%# Comments - they are discarded from source %>

All expressions that output something to the template must use the equals sign (=). Since everything in Elixir is an expression, there are no exceptions for this rule. For example, while some template languages would special-case if/2 clauses, they are treated the same in EEx and also require = in order to have their result printed:

<%= if true do %>
  It is obviously true
<% else %>
  This will never appear
<% end %>

Notice that different engines may have different rules for each tag. Other tags may be added in future versions.

Macros

EEx.SmartEngine also adds some macros to your template. An example is the @ macro which allows easy data access in a template:

iex> EEx.eval_string "<%= @foo %>", assigns: [foo: 1]
"1"

In other words, <%= @foo %> translates to:

<%= {:ok, v} = Access.fetch(assigns, :foo); v %>

The assigns extension is useful when the number of variables required by the template is not specified at compilation time.

Link to this section Summary

Functions

compile_file(filename, options \\ [])

Gets a filename and generate a quoted expression that can be evaluated by Elixir or compiled to a function

compile_string(source, options \\ [])

Gets a string source and generate a quoted expression that can be evaluated by Elixir or compiled to a function

eval_file(filename, bindings \\ [], options \\ [])

Gets a filename and evaluate the values using the bindings

eval_string(source, bindings \\ [], options \\ [])

Gets a string source and evaluate the values using the bindings

function_from_file(kind, name, file, args \\ [], options \\ [])

Generates a function definition from the file contents

function_from_string(kind, name, source, args \\ [], options \\ [])

Generates a function definition from the string

Link to this section Functions

Link to this function compile_file(filename, options \\ []) View Source 
compile_file(String.t(), keyword()) :: Macro.t() | no_return()

Gets a filename and generate a quoted expression that can be evaluated by Elixir or compiled to a function.

Link to this function compile_string(source, options \\ []) View Source 
compile_string(String.t(), keyword()) :: Macro.t() | no_return()

Gets a string source and generate a quoted expression that can be evaluated by Elixir or compiled to a function.

Link to this function eval_file(filename, bindings \\ [], options \\ []) View Source 
eval_file(String.t(), keyword(), keyword()) :: any()

Gets a filename and evaluate the values using the bindings.

Examples 

# sample.eex
foo <%= bar %>

# iex
EEx.eval_file "sample.eex", [bar: "baz"] #=> "foo baz"
Link to this function eval_string(source, bindings \\ [], options \\ []) View Source 
eval_string(String.t(), keyword(), keyword()) :: any()

Gets a string source and evaluate the values using the bindings.

Examples 

iex> EEx.eval_string "foo <%= bar %>", [bar: "baz"]
"foo baz"
Link to this macro function_from_file(kind, name, file, args \\ [], options \\ []) View Source (macro)

Generates a function definition from the file contents.

The kind (:def or :defp) must be given, the function name, its arguments and the compilation options.

This function is useful in case you have templates but you want to precompile inside a module for speed.

Examples 

# sample.eex
<%= a + b %>

# sample.ex
defmodule Sample do
  require EEx
  EEx.function_from_file :def, :sample, "sample.eex", [:a, :b]
end

# iex
Sample.sample(1, 2) #=> "3"
Link to this macro function_from_string(kind, name, source, args \\ [], options \\ []) View Source (macro)

Generates a function definition from the string.

The kind (:def or :defp) must be given, the function name, its arguments and the compilation options.

Examples 

iex> defmodule Sample do
...>   require EEx
...>   EEx.function_from_string :def, :sample, "<%= a + b %>", [:a, :b]
...> end
iex> Sample.sample(1, 2)
"3"