Switch from Jinja to Scriggo

This page is targeted to users who are already familiar with designing templates in Python/Jinja but have a limited/no experience with Go/Scriggo.

Here is provided a overview of the similarities and the differences between the two templating languages.

Some examples on this page are taken from the Jinja documentation (copyright 2007 Pallets).

Syntax

Jinja and Scriggo share the same syntax for enclosing statements, rendering expressions and commenting.

  • {% .. %} for statements
  • {{ .. }} for expressions
  • {# .. #} for comments

Some statements need an end tag to be closed.

For example:

{% if condition %}
    ...
{% end %}

Note that in Scriggo, unlike Jinja, the statement name is optional and, if provided, it must be separated by the end keyword:

{% if condition %}
    ...
{% end if %}

Type system

One of the biggest differences between Jinja and Scriggo is the type system.

Jinja is based on Python, thus it offers a dynamically-typed template system, while Scriggo (which is based on Go) is statically typed.

This means that, when writing templates in Scriggo, most of the errors will be catch at compile time.

For example, writing this code in Scriggo:

{% var name string = "hello" %}
{% name = 23 %}                     {# ← WRONG! #}

results in a compilation error like this:

cannot use 23 (type untyped int) as type string in assignment

Escaping

Like in Jinja, the easiest way to output a string that is part of the Scriggo syntax is putting it inside a string literal and showing it:

{{ "{{" }}

For bigger sections, Scriggo makes available the raw block that acts the same as the raw block in Jinja:

{% raw %}
    <ul>
    {% for item in seq %}
        <li>{{ item }}</li>
    {% end for %}
    </ul>
{% end raw %}

Note that the raw block is closed by {% end raw %}, not {% endraw %}.

Tests

Since Scriggo implements a full programming language, tests can be performed using any valid expression.

For example this test in Jinja:

{% if loop.index is divisibleby 3 %}

can be rewritten in Scriggo simply using arithmetic and comparison operators:

{% if loop.index % 3 == 0 %}

Comments

In Scriggo, just like Jinja, you can write commented code enclosing it between {# and #}. Commented portions of the template won't be rendered by Scriggo.

Note that Scriggo, unlike Jinja, supports nested comments:

{#  {# This is a nested comment! #}  #}

Expressions

Literals

Strings

Strings, in Scriggo, can be enclosed between double quotation marks or backticks.

For example, these are valid string literals in Scriggo:

{{ "hello" }}
{{ `hi!` }}

The single quotation mark is used to denote a rune, thus it can only enclose one character:

{% var mychar = 's' %}
{{ mychar }}

Lists

Scriggo has a typed list type called slice, where the type must be specified at compilation-time. Also, slice elements must be enclosed between { and } instead of [ and ].

For example this code in Jinja:

{% set l = [1, 2, 3] %}

can be written in Scriggo as:

{% var l = []int{1, 2, 3} %}

Dictionaries

Scriggo has a typed dictionary type called map, where both the key and the value types must be specified at compile-time.

So, this dictionary:

{% set data = {'dict': 'of', 'key': 'and', 'value': 'pairs'} %}

can be written as:

{% var data = map[string]string{"dict": "of", "key": "and", "value": "pairs"} %}

Note that maps in Scriggo, just like in Go, do not keep any information about keys ordering.

Tuples

Scriggo has no equivalent for tuples. In general, you may want to use slices for sorted values, and maps or structs for values with an associated key.

For example, consider this tuple in Jinja, representing a date:

{% set birthday = (1, 5, 2020) %}

This can be rewritten in Scriggo using a slice:

{% var birthday = []int{1, 5, 2020} %}

or, if you want named values, you can use a map:

{% var birthday = map[string]int{"day": 1, "month": 5, "year": 2020} %}

or a struct:

{% type date struct { day, month, year int } %}
{% var birthday = date{day: 1, month: 5, year: 2020} %}

If Expression

While Jinja does have if expressions, Scriggo doesn't.

In Scriggo you can use an if statement to assign to a variable conditionally:

{% var title = "bar" %}
{% if 2 + 2 == 4 %}
    {% title = "foo" %}
{% end %}
<h1>{{ title }}</h1>

Math and comparisons

Scriggo and Jinja shares a big part of their operators.

For example this template code is valid both in Jinja and Scriggo:

{{ 3 + 10 }} {{ 32 - 2 }} {{ 5 / 2.5 }} {{ 11 % 2 }}
{{ 24 == (2 + 5) }} {{ 1 < 4 }}

Logic

Scriggo, just like Jinja, supports the and, or and not logic operators, but with a difference: while in Jinja (like in Python) the and and or expressions are evaluated as one of the two operands, in Scriggo they are always evaluated to a boolean value.

Consider this:

{{ 0 or "hello" }}

Jinja renders:

hello

while Scriggo renders:

true

The behavior of the not operator is the same in Jinja and Scriggo, thus it always evaluates to a boolean.

Operator in

While Jinja has the in operator:

{{ 1 in [1, 2, 3] }}
{{ 3 not in [1, 2, 3] }}

Scriggo has the contains and not contains operators (note that the operands are reverted respect to the in operator):

{{ []int{1, 2, 3} contains 1 }}
{{ []int{1, 2, 3} not contains 3 }}

Operator + (plus)

The operator + in Scriggo, just like in Jinja, can also be used to concatenate strings.

{% var name = "hello" %}
{{ name + ", " + "world!" }}

Operator ~ (tilde)

Jinja has the tilde operator that converts the operands in strings and concatenates them:

{% set name = "FooBar" %}
{{ "Hello " ~ name ~ "!" }}

In Scriggo this can be achieved using a built-in function like sprintf:

{% var name = "FooBar" %}
{{ sprintf("Hello %s!", name) }}

If the operands are strings, you can use the operator +.

Methods

In Scriggo, just like in Jinja, you can call methods on values using the syntax:

{{ value.Method(a1, a2) }}

List of control structures

For

Scriggo supports the for loop syntax used in Jinja, plus the ones used in Go.

For example this for loop in Jinja:

<h1>Members</h1>
<ul>
{% for user in users %}
  <li>{{ user.username }}</li>
{% endfor %}
</ul>

can be rewritten in Scriggo just changing the closing tag:

<h1>Members</h1>
<ul>
{% for user in users %}
  <li>{{ user.username }}</li>
{% end for %}
</ul>

If

Scriggo has the if statement with optional else. The condition can be any expression of any type.

Here are some examples:

{% if 2 + 2 == 4 %}
    Well!
{% else %}
    Bad...
{% end if %}
{% var primes = []int{2, 3, 5, 7, 11, 13} %}
{% var n = 5 %}
{% if primes contains n %}
    {{ n }} is prime.
{% end if %}

Block Assignments

Scriggo provides a mechanism similar to the block assignments in Jinja, through the using statement and the itea built-in identifier.

So, for example, this code in Jinja:

{% set navigation %}
    <li><a href="/">Index</a>
    <li><a href="/downloads">Downloads</a>
{% endset %}

can be reproduced in Scriggo as:

{% var navigation = itea; using %}
    <li><a href="/">Index</a>
    <li><a href="/downloads">Downloads</a>
{% end using %}

Since itea is an identifier, it can be used in any expression, so it can also be passed as argument to builtin functions as you use filters in the block assignments in Jinja:

{% set reply|upper %}
    You wrote:
    {{ message }}
{% endset %}

becomes in Scriggo:

{% var reply = toUpper(itea); using string %}
    You wrote:
    {{ message }}
{% end using %}

Calls

Call blocks can be reproduced in Scriggo using the using and show statements and the itea built-in identifier.

For example this code in Jinja:

{% macro render_dialog(title) %}
    <div>
        <h2>{{ title }}</h2>
        <div class="contents">
            {{ caller() }}
        </div>
    </div>
{% endmacro %}

{% call render_dialog('Hello World') %}
    This is a simple dialog rendered by using a macro and
    a call block.
{% endcall %}

can be reproduce in Scriggo as:

{% macro render_dialog(title string, contents macro() html) %}
    <div>
        <h2>{{ title }}</h2>
        <div class="contents">
            {{ contents() }}
        </div>
    </div>
{% end macro %}

{% show render_dialog("Hello World", itea); using macro() html %}
    This is a simple dialog rendered by using a macro and
    a call block.
{% end using %}

The {% show .. %} statement is equivalent to {{ .. }}, but the former is mandatory when used in combination with the using statement.

Filters

Filters can be rewritten in Scriggo using built-in functions and syntactic constructs.

See built-in filters for some examples.

Assignments

In Jinja, you can assign values to variables using the set statement:

{% set navigation = "x.html" %}
{% set navigation = "y.html" %}
{% set key, value = call_something() %}

In Scriggo (just like in Go) there are two main differences:

  • variables must be declared before being assigned
  • when declaring a variable, the var keyword is used instead of set

So the example above becomes:

{% var navigation = "x.html" %}
{% navigation = "y.html" %}
{% var key, value = call_something() %}

Scriggo (like Go) also supports the short variable declaration operator :=, which is not covered in this document.

Template inheritance

Just like Jinja, Scriggo provides a mechanism to implement the template inheritance.

The extends declaration can be used in Scriggo to extend another file, just like in Jijnja:

{% extends "layout/default.html" %}

Blocks and macros

Both the blocks and the macros of Jinja can be implemented in Scriggo using the flexible system of macros.

For example, consider this template file in Jinja that extends another file:

{% extends "base.html" %}
{% block title %}Index{% endblock %}
{% block head %}
    {{ super() }}
    <style type="text/css">
        .important { color: #336699; }
    </style>
{% endblock %}
{% block content %}
    <h1>Index</h1>
    <p class="important">
      Welcome to my awesome homepage.
    </p>
{% endblock %}

In Scriggo it becomes:

{% extends "base.html" %}
{% macro Title %}Index{% end macro %}
{% macro Head(super macro()) %}
    {{ super() }}
    <style type="text/css">
        .important { color: #336699; }
    </style>
{% end macro %}
{% macro Content() %}
    <h1>Index</h1>
    <p class="important">
      Welcome to my awesome homepage.
    </p>
{% end macro %}

Macros in Scriggo, just like macros in Jinja, can accept parameters.

So, this template in Jinja:

{% macro input(name, value='', type='text', size=20) %}
    <input type="{{ type }}" name="{{ name }}" value="{{
        value|e }}" size="{{ size }}">
{% endmacro %}

{{ input("Car", "Red & Blue", size=30) }}

can be written in Scriggo as:

{% macro input(name, value, typ string, size int) %}
    {% if typ == "" %}{% typ = "text" %}{% end if %}
    {% if size == 0 %}{% size = 20 %}{% end if %}
    <input type="{{ typ }}" name="{{ name }}" value="{{
        value }}" size="{{ size }}">
{% end macro %}

{{ input("Car", "Red & Blue", "", 30) }}

As you may have noticed, there are some main differences:

  • Scriggo macros declarations, just like function declarations in Go, does not provide a default mechanism for parameters, so their value must be explicitly set in the body of the macro.
  • The types of the parameters, in Scriggo, must be explicitly declared. The compiler will check if the types of the argument passed to the macro call match the types of the parameters.
  • Scriggo, just like Go, does not have named parameters.

Including other template files

Jinja uses the include statement:

{% include 'header.html' %}

Scriggo uses a more flexible system making available the render operator that reads a template file and returns its rendered content.

So, the example above may be written as:

{{ render "header.html" }}

The value returned by render can be used in any expression:

{% var content = render "myfile.html" %}
File is {{ len(content) }} bytes long.

Importing other template files

Scriggo has the import declaration, just like Jinja, but with some differences.

There are several form of import available.

To import a template file specifying the declarations to import:

{% import "path/to/file.html" for Title, Content %}
{{ Title() }}
{{ Content() }}

To import every (exported) declaration from a template file:

{% import "path/to/file.html" %}
{{ Title() }}
{{ Content() }}

To import a template file, prepending a prefix to the imported declarations:

{% import myfile "path/to/file.html" %}
{{ myfile.Title() }}
{{ myfile.Content() }}

List of built-in filters

To get an overview about filters, see the corresponding section.

Here are just some examples:

abs

Jinja:

{{ -3|abs }}

Scriggo has the built-in function abs:

{{ abs(-3) }}

attr

Jijna

{{  foo|attr("bar") }}

In Scriggo you can access to attributes using a selector, just like in Jinja:

{{  foo.bar }}

Note that if foo has no attribute bar, it results in a compilation error.

In general, attributes names in Scriggo begins with an uppercase letter: that means that such field is exported. In Scriggo, just like in Go, only exported fields can be accessed by other packages from the one that declared such type.

length

Scriggo offer the built-in function runeCount that returns the number of characters of a string.

{{ runeCount("hellò") }}

renders to

5

Scriggo also offers the built-in function len that returns the number of elements in slices and maps and the number of bytes in strings.

{{ len([]int{10, 20, 30}) }}
{{ len("hellò") }}

renders to:

3
6

HTML Escaping

In Jinja the escaping can be achieved both manually (using the e filter) or automatically.

In Scriggo the code is always escaped before being rendered in a given context.

For example:

{{ "<b>Not real bold...</b>" }}

renders as:

&lt;b&gt;Not real bold...&lt;/b&gt;

This happens because the rendered value has type string, so it must be escaped before being rendered in a HTML context.

For this reason, if you write something like:

{{ html("<b>Real bold!</b>") }}

this is rendered as:

<b>Real bold!</b>

because the value type is explicitly set to the html type, so Scriggo won't escape it.

Automatic contextual escaping

Scriggo also offers an automatic contextual escaping. For example consider this:

{% var value = "< is more" %}
<p>{{ value }}</p>
<a href="{{ value }}"></a>

It is rendered as:

<p>&lt; is more</p>
<a href="%3c is more"></a>

As you may notice, the string < is more is automatically escaped using two different algorithms:

  • in the context of HTML it becomes: &lt; is more.
  • in the context of an attribute value, that is automatically detected by the Scriggo parser, it is escaped as %3c is more.

Continue to learn

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