ECR
module ECR
Overview
Embedded Crystal (ECR) is a template language for embedding Crystal code into other text, that includes but is not limited to HTML. The template is read and transformed at compile time and then embedded into the binary.
There are and syntax. The former will render returned values. The latter will not, but instead serve to control the structure as we do in Crystal.
Using a dash inside <...>
either eliminates previous indentation or removes the next newline:
- : removes previous indentation
- : removes next newline
- : removes previous indentation
- : removes next newline
Quick Example:
require "ecr" class Greeting def initialize(@name : String) end ECR.def_to_s "greeting.ecr" end # greeting.ecr Greeting, <%= @name %>! Greeting.new("John").to_s #=> Greeting, John!
Using logical statements:
# greeting.ecr <%- if @name -%> Greeting, <%= @name %>! <%- else -%> Greeting! <%- end -%> Greeting.new(nil).to_s #=> Greeting!
Using loops:
require "ecr" class Greeting @names : Array(String) def initialize(*names) @names = names.to_a end ECR.def_to_s "greeting.ecr" end # greeting.ecr <%- @names.each do |name| -%> Hi, <%= name %>! <%- end -%> Greeting.new("John", "Zoe", "Ben").to_s #=> Hi, John! #=> Hi, Zoe! #=> Hi, Ben!
Likewise, other Crystal logic can be implemented in ECR text.
Defined in:
ecr.crecr/macros.cr
Macro Summary
- def_to_s(filename)
Defines a
to_s(io)
method whose body is the ECR contained in filename, translated to Crystal code. - embed(filename, io_name)
Embeds an ECR file contained in filename into the program.
Macro Detail
macro def_to_s(filename)Source
Defines a to_s(io)
method whose body is the ECR contained in filename, translated to Crystal code.
# greeting.ecr Hello <%= @name %>!
require "ecr/macros" class Greeting def initialize(@name : String) end ECR.def_to_s "greeting.ecr" end Greeting.new("World").to_s # => "Hello World!"
The macro basically translates the text inside the given file to Crystal code that appends to the IO:
class Greeting def to_s(io) io << "Hello " io << @name io << "!" end end
macro embed(filename, io_name)Source
Embeds an ECR file contained in filename into the program.
The generated code is the result of translating the contents of the ECR file to Crystal, a program that appends to the IO with the given io_name.
# greeting.ecr Hello <%= name %>!
require "ecr/macros" name = "World" io = IO::Memory.new ECR.embed "greeting.ecr", io io.to_s # => "Hello World!"
The ECR.embed
line basically generates this:
io << "Hello " io << name io << "!"
© 2012–2017 Manas Technology Solutions.
Licensed under the Apache License, Version 2.0.
https://crystal-lang.org/api/0.22.0/ECR.html