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# Go Liquid Template Parser
[![GoDoc](https://godoc.org/github.com/osteele/liquid?status.svg)](http://godoc.org/github.com/osteele/liquid)
`goliquid` is a pure Go implementation of [Shopify Liquid templates](https://shopify.github.io/liquid), for use in [gojekyll](https://github.com/osteele/gojekyll).
## Status
[![Build Status](https://travis-ci.org/osteele/liquid.svg?branch=master)](https://travis-ci.org/osteele/liquid)
[![Go Report Card](https://goreportcard.com/badge/github.com/osteele/liquid)](https://goreportcard.com/report/github.com/osteele/liquid)
[![GoDoc](https://godoc.org/github.com/osteele/liquid?status.svg)](http://godoc.org/github.com/osteele/liquid)
`liquid` is a pure Go implementation of [Shopify Liquid templates](https://shopify.github.io/liquid), for use in [gojekyll](https://github.com/osteele/gojekyll).
It supports a functional API for defining tags and filters. On the one hand, this isn't idiomatic Go. On the other hand, this made it possibly to quickly implement a boatload of Liquid and Jekyll filters that would otherwise have been onerous. The jury is still out…
<!-- TOC -->
- [Go Liquid Template Parser](#go-liquid-template-parser)
- [Status](#status)
- [Install](#install)
- [Contribute](#contribute)
- [Setup](#setup)
- [Workflow](#workflow)
- [Working on the Parser and Lexer](#working-on-the-parser-and-lexer)
- [References](#references)
- [Attribution](#attribution)
- [Other Implementations](#other-implementations)
- [Go](#go)
- [Other Languages](#other-languages)
- [License](#license)
<!-- /TOC -->
## Status
This library is in its early days. IMO it's not sufficiently mature to be worth snapping off a [versioned URL](http://labix.org/gopkg.in). In particular, the tag and filter extension API is likely to change.
- [ ] Basics
- [x] Literals
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- [ ] Control Flow
- [x] `if`/`else`/`elsif`
- [x] `unless`
- [ ] `case`
- [x] `case`
- [x] `when`
- [ ] `else`
- [ ] Iteration
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make setup
```
Install Ragel. On macOS: `brew install ragel`.
### Workflow
```bash
go generate ./...
go test ./...
```
@ -72,37 +91,48 @@ godoc -http=:6060&
open http://localhost:6060/pkg/github.com/osteele/liquid/
```
### Working on the Parser and Lexer
To work on the lexer, install Ragel. On macOS: `brew install ragel`.
Do this after editing `scanner.rl` or `expressions.y`:
```bash
go generate ./...
```
## References
<https://shopify.github.io/liquid>
<https://help.shopify.com/themes/liquid>
<https://github.com/Shopify/liquid/wiki/Liquid-for-Designers>
* [Shopify.github.io/liquid](https://shopify.github.io/liquid) is the definitive reference.
* [Help.shopify.com](https://help.shopify.com/themes/liquid) goes into more detail, but includes features that aren't present in core Liquid as used by Jekyll.
* Shopify's [Liquid for Designers](https://github.com/Shopify/liquid/wiki/Liquid-for-Designers) is another take.
## Attribution
| Package | Author | Description |
| --- | --- | --- |
| [gopkg.in/yaml.v2](https://github.com/go-yaml) | Canonical | YAML support |
| [Ragel](http://www.colm.net/open-source/ragel/) | Adrian Thurston | scanning expressions |
| Package | Author | Description | License |
|-------------------------------------------------------|-----------------|----------------------------------------------|--------------------|
| [gopkg.in/yaml.v2](https://github.com/go-yaml/yaml) | Canonical | YAML support (for printing parse trees) | Apache License 2.0 |
| [jeffjen/datefmt](https://github.com/jeffjen/datefmt) | Jeffrey Jen | Go bindings to GNU `strftime` and `strptime` | MIT |
| [Ragel](http://www.colm.net/open-source/ragel/) | Adrian Thurston | scanning expressions | MIT |
Michael Hamrah's [Lexing with Ragel and Parsing with Yacc using Go](https://medium.com/@mhamrah/lexing-with-ragel-and-parsing-with-yacc-using-go-81e50475f88f) was essential to understanding `go yacc`.
The [original Liquid engine](https://shopify.github.io/liquid), of course, for the design and documentation of the Liquid template language. Many of the tag and filter test cases are taken directly from the Liquid documentation.
(That said, this is a clean-room implementation to make sure it just implements the documented design.)
## Other Implementations
Go:
### Go
* <https://godoc.org/github.com/karlseguin/liquid> is a partial implementation.
* <https://godoc.org/github.com/acstech/liquid> is a more active fork of Karl Seguin's implementation.
* <https://godoc.org/github.com/hownowstephen/go-liquid> is a more recent entry.
* [karlseguin/liquid](https://github.com/karlseguin/liquid) is a dormant implementation that inspired a lot of forks.
* [acstech/liquid](https://github.com/acstech/liquid) is a more active fork of Karl Seguin's implementation. I submitted a couple of pull requests there.
* [hownowstephen/go-liquid](https://github.com/hownowstephen/go-liquid) is a more recent entry.
<https://github.com/Shopify/liquid/wiki/Ports-of-Liquid-to-other-environments> lists ports to other languages.
After trying each of these, and looking at how to extend them, I concluded that I wasn't going to get very far without a parser generator. I also wanted an easy API for writing filters.
### Other Languages
See Shopify's [ports of Liquid to other environments](https://github.com/Shopify/liquid/wiki/Ports-of-Liquid-to-other-environments).
## License