slang.

iyi get github.com/domify/slang

Slang

Lightweight, terse templates for iyi, in the syntax of Slim.

Slang started in 2016 as a template language for Crystal. This repository is its continuation as a native iyi module: the lexer, parser and code generation of the last Crystal release (2.0.3) are ported to iyi, along with its tests. The Crystal code is kept unchanged in archive/crystal/ and is no longer maintained. The iyi port is maintained by Priit Tark at domify.

Like the original, a template is turned into iyi code at compile time, so a rendered page is ordinary compiled code by the time the program runs.

Installation

iyi get github.com/domify/slang

Usage

import github.com/domify/slang::{Slang}

def page(name : String, items : Array(String)) : String
  Slang.render("views/page.slang")
end

Slang.render("file.slang") is the rendered template as a String. Slang.embed("file.slang", io) writes it to io, anything with <<, such as a String::Builder. The path is read beside the file that calls the macro, or as it is when absolute. Local variables of the method that renders a template are visible in it.

TEMPLATES.md is a short guide to writing templates, for agents and people who know Slim; AGENTS.md is for working on Slang itself.

Syntax

doctype html
html lang="en"
  head
    meta charset="utf-8"
    title= title
    css:
      h1 {color: red;}
  body
    /! A visible comment
    / An invisible comment
    h1.title Hello, #{name}!
    p
      ' Text is <em>HTML</em>,
      | and #{name} in it is escaped.
    div!= "<hr>"
    ul#items
      - items.each do |item|
        li class=(item == current ? "current" : nil) = item
    input type="checkbox" checked=true
    input type="checkbox" checked=false
    a(href="/about" title="About") About
    span<> spaced
    javascript:
      console.log("8 * 3 =", 8 * 3);

With title = "Slang", name = "<world>", items = ["one", "two"] and current = "two", this renders as (one line, broken here for reading):

<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><title>Slang</title>
<style>h1 {color: red;}</style></head><body><!--A visible comment-->
<h1 class="title">Hello, &lt;world&gt;!</h1>
<p>Text is <em>HTML</em>, and &lt;world&gt; in it is escaped.</p><div><hr></div>
<ul id="items"><li>one</li><li class="current">two</li></ul>
<input type="checkbox" checked><input type="checkbox">
<a href="/about" title="About">About</a> <span>spaced</span>
<script>console.log("8 * 3 =", 8 * 3);</script></body></html>

As in Slim, there is no whitespace between tags. An attribute value without quotes ends at the first space outside parentheses or brackets, so compute a long expression in a - name = … line first. For the same reason, output after such a value needs a space before its =, as in li class=css = item; after a tag or a quoted value, p= name and a href="/"= name need non

Differences from Crystal Slang 2.0.3

• Raw output is !=, as in Haml and Pug, so it does not read as a comparison; == stops the template with an error.
• An attribute whose value is false or nil is left out and true writes the bare name, including id and the entries of a *splat hash.
• Blank class names are left out, and an element without a class name has no class attribute.
• iyi: opens a code block, as crystal: does.
• begin/rescue lines are parsed, but iyi has no exceptions, so they do not compile. Kilt and Kemal's content_for are not supported.
• Fixed bugs of the original:
• =< and => put a space before and after the output; the original added it to the code.
• Comparisons such as a == b and a != b inside an attribute value are kept; the original dropped every = in it.
• An attribute value such as (f(x) == y) no longer ends at the space after the inner ).
• Attributes after a(href="x") no longer stop the template with "Missing hash key: ')'".
• A compile error in a template's code names the template's line.

Development

iyi test

slang_test.iyi holds the tests of the Crystal shard's spec/slang_spec.cr, with their templates under spec/, and the port's own additions. The module is slang.iyi (what rendered code needs at run time, and the macros) and slang/process.iyi (the lexer, parser and code generation the macros run at compile time).

Thanks

Slang exists because of the people who wrote and kept it alive:

• Jerome Gravel-Niquet created Slang in 2016 and maintained it as jeromegn/slang.
• Todd Sundsted maintained the fork toddsundsted/slang from 2020 to 2026 and made Slang 2.0: Slim's whitespace and escaping rules, blocks, case … in, splat attributes and a thorough test suite. This port follows his code closel
• Everyone else who contributed: Dmitry Neveshkin, Anton Maminov, Isaac Sloan, Cris Ward, Florin Lipan, Ivan, Sergey Makridenkov, SlayerShadow, TSUYUSATO Kitsune, V. Elenhaupt, beno and nashimoto.

Their history is in this repository's git log.

License

MIT, see LICENSE.