What is Yate?

Yate stands for Yet Anoter Template Engine and is a Haskell library. It is a agnostic meaning it doesn't know anything about any particular output format. It is therefore not suitable for everything, e.g. XSS issues in HTML files.

Example

NB: We'll use JSON herefor the sake of simplicity, but you can use your own data structures by instanciating the typeclass ToYate.

template.txt

Items owned by {%= author.name %}:
{% forall items %}
* {%= .description %}{% if .value %} ({%= .value %}){%end}
{% end %}

data.json

{
  "author": {
    "name": "Tom"
  },
  "items": [
    {
      "description": "Item 1",
      "value": 11.99
    },
    {
      "description": "Item 2"
    }
  ]
}

Main.hs

{-# LANGUAGE TemplateHaskell #-}

import           Data.Aeson
import qualified Data.ByteString.Lazy.Char8 as BSL

import           Text.Yate

template :: Template Value
template = $(loadTemplateFile "template.txt")

main :: IO ()
main = do
  jsonContent <- BSL.readFile "data.json"
  Just  dat   <- decode jsonContent
  Right out   <- renderTemplate template dat
  putStrLn out

Output

Items owned by Tom:
* Item 1 (11.99)
* Item 2

Syntax

Paths

Absolute paths are of the form a.b.c and describe the path to traverse in the data structure to get a certain element. Relative paths have the same function but start from the current object (see in and forall.)

Variable insertion

This is as simple as {%= PATH %}.

If statement

{% if PATH %}
  Block 1
{% else %}
  Block 2
{% end %}

or

{% if PATH %}
  Block
{% end %}

For statement

{% for NAME in PATH %}
  Block
{% end %}

A variable called NAME is added to the main object in the evaluation of the block. Thus, it is accessible with absolute paths.

In statement

{% in PATH %}
  Block
{% end %}

The current object for relative paths is changed to the one accessible with the given path.

Forall statement

{% forall PATH %}
  Block
{% end %}

is some syntactic sugar for:

{% for _element in PATH %}{% in _element %}
  Block
{% end %}{% end %}

Note about variable names

Characters allowed in names are alphanumeric characters as well as -~!@#$%^&*_+=;:'?.

API Documentation

See https://hackage.haskell.org/package/yate for more information.