gobuffalo / Plush
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Plush 
Plush is the templating system that Go both needs and deserves. Powerful, flexible, and extendable, Plush is there to make writing your templates that much easier.
Installation
$ go get -u github.com/gobuffalo/plush
Usage
Plush allows for the embedding of dynamic code inside of your templates. Take the following example:
<!-- input -->
<p><%= "plush is great" %></p>
<!-- output -->
<p>plush is great</p>
Controlling Output
By using the <%= %> tags we tell Plush to dynamically render the inner content, in this case the string plush is great, into the template between the <p></p> tags.
If we were to change the example to use <% %> tags instead the inner content will be evaluated and executed, but not injected into the template:
<!-- input -->
<p><% "plush is great" %></p>
<!-- output -->
<p></p>
By using the <% %> tags we can create variables (and functions!) inside of templates to use later:
<!-- does not print output -->
<%
let h = {name: "mark"}
let greet = fn(n) {
return "hi " + n
}
%>
<!-- prints output -->
<h1><%= greet(h["name"]) %></h1>
Full Example:
html := `<html>
<%= if (names && len(names) > 0) { %>
<ul>
<%= for (n) in names { %>
<li><%= capitalize(n) %></li>
<% } %>
</ul>
<% } else { %>
<h1>Sorry, no names. :(</h1>
<% } %>
</html>`
ctx := plush.NewContext()
ctx.Set("names", []string{"john", "paul", "george", "ringo"})
s, err := plush.Render(html, ctx)
if err != nil {
log.Fatal(err)
}
fmt.Print(s)
// output: <html>
// <ul>
// <li>John</li>
// <li>Paul</li>
// <li>George</li>
// <li>Ringo</li>
// </ul>
// </html>
Comments
You can add comments like this:
<%# This is a comment %>
If/Else Statements
The basic syntax of if/else if/else statements is as follows:
<%
if (true) {
# do something
} else if (false) {
# do something
} else {
# do something else
}
%>
When using if/else statements to control output, remember to use the <%= %> tag to output the result of the statement:
<%= if (true) { %>
<!-- some html here -->
<% } else { %>
<!-- some other html here -->
<% } %>
Operators
Complex if statements can be built in Plush using "common" operators:
-
==- checks equality of two expressions -
!=- checks that the two expressions are not equal -
~=- checks a string against a regular expression (foo ~= "^fo") -
<- checks the left expression is less than the right expression -
<=- checks the left expression is less than or equal to the right expression -
>- checks the left expression is greater than the right expression -
>=- checks the left expression is greater than or equal to the right expression -
&&- requires both the left and right expression to be true -
||- requires either the left or right expression to be true
Grouped Expressions
<%= if ((1 < 2) && (someFunc() == "hi")) { %>
<!-- some html here -->
<% } else { %>
<!-- some other html here -->
<% } %>
Maps
Maps in Plush will get translated to the Go type map[string]interface{} when used. Creating, and using maps in Plush is not too different than in JSON:
<% let h = {key: "value", "a number": 1, bool: true} %>
Would become the following in Go:
map[string]interface{}{
"key": "value",
"a number": 1,
"bool": true,
}
Accessing maps is just like access a JSON object:
<%= h["key"] %>
Using maps as options to functions in Plush is incredibly powerful. See the sections on Functions and Helpers to see more examples.
Arrays
Arrays in Plush will get translated to the Go type []interface{} when used.
<% let a = [1, 2, "three", "four", h] %>
[]interface{}{ 1, 2, "three", "four", h }
For Loops
There are three different types that can be looped over: maps, arrays/slices, and iterators. The format for them all looks the same:
<%= for (key, value) in expression { %>
<%= key %> <%= value %>
<% } %>
The values inside the () part of the statement are the names you wish to give to the key (or index) and the value of the expression. The expression can be an array, map, or iterator type.
Arrays
Using Index and Value
<%= for (i, x) in someArray { %>
<%= i %> <%= x %>
<% } %>
Using Just the Value
<%= for (val) in someArray { %>
<%= val %>
<% } %>
Maps
Using Index and Value
<%= for (k, v) in someMap { %>
<%= k %> <%= v %>
<% } %>
Using Just the Value
<%= for (v) in someMap { %>
<%= v %>
<% } %>
Iterators
type ranger struct {
pos int
end int
}
func (r *ranger) Next() interface{} {
if r.pos < r.end {
r.pos++
return r.pos
}
return nil
}
func betweenHelper(a, b int) Iterator {
return &ranger{pos: a, end: b - 1}
}
html := `<%= for (v) in between(3,6) { return v } %>`
ctx := plush.NewContext()
ctx.Set("between", betweenHelper)
s, err := plush.Render(html, ctx)
if err != nil {
log.Fatal(err)
}
fmt.Print(s)
// output: 45
Helpers
For a full list, and documentation of, all the Helpers included in Plush, see github.com/gobuffalo/helpers.
Custom Helpers
html := `<p><%= one() %></p>
<p><%= greet("mark")%></p>
<%= can("update") { %>
<p>i can update</p>
<% } %>
<%= can("destroy") { %>
<p>i can destroy</p>
<% } %>
`
ctx := NewContext()
// one() #=> 1
ctx.Set("one", func() int {
return 1
})
// greet("mark") #=> "Hi mark"
ctx.Set("greet", func(s string) string {
return fmt.Sprintf("Hi %s", s)
})
// can("update") #=> returns the block associated with it
// can("adsf") #=> ""
ctx.Set("can", func(s string, help HelperContext) (template.HTML, error) {
if s == "update" {
h, err := help.Block()
return template.HTML(h), err
}
return "", nil
})
s, err := Render(html, ctx)
if err != nil {
log.Fatal(err)
}
fmt.Print(s)
// output: <p>1</p>
// <p>Hi mark</p>
// <p>i can update</p>
Special Thanks
This package absolutely 100% could not have been written without the help of Thorsten Ball's incredible book, Writing an Interpeter in Go.
Not only did the book make understanding the process of writing lexers, parsers, and asts, but it also provided the basis for the syntax of Plush itself.
If you have yet to read Thorsten's book, I can't recommend it enough. Please go and buy it!