This is a Haskell implementation of Mustache templates. The implementation conforms to version 1.1.3 of the official Mustache specification. It has a minimal but complete API—three functions to compile templates (from a directory, from a file, and from lazy text) and one to render them.

The implementation uses the Megaparsec parsing library to parse the templates, which results in high-quality error messages.

For rendering one only needs to create an Aeson Value that is used for interpolation of template variables. Since the library re-uses Aeson's instances and most data types in the Haskell ecosystem are instances of classes like Data.Aeson.ToJSON, the process is simple for the end user.

Template Haskell helpers for compilation of templates at compile time are available in the Text.Mustache.Compile.TH module.

One feature that is not currently supported is lambdas. The feature is marked as optional in the spec and can be emulated via processing of the parsed template representation. The decision to drop lambdas is intentional, for the sake of simplicity and better integration with Aeson.

Usage

Here is an example of basic usage:

{-# LANGUAGE OverloadedStrings #-}
module Main (main) where
import Data.Aeson
import Data.Text
import Text.Megaparsec
import Text.Mustache
import qualified Data.Text.Lazy.IO as TIO
main :: IO ()
main = do
  let res = compileMustacheText "foo"
        "Hi, {{name}}! You have:\n{{#things}}\n  * {{.}}\n{{/things}}\n"
  case res of
    Left bundle -> putStrLn (errorBundlePretty bundle)
    Right template -> TIO.putStr $ renderMustache template $ object
      [ "name"   .= ("John" :: Text)
      , "things" .= ["pen" :: Text, "candle", "egg"]
      ]

If I run the program, it prints the following:

Hi, John! You have:
  * pen
  * candle
  * egg

For more information about Mustache templates the following links may be helpful:

The official Mustache site: https://mustache.github.io/
The manual: https://mustache.github.io/mustache.5.html
The specification: https://github.com/mustache/spec
Stack Builders Stache tutorial: https://www.stackbuilders.com/tutorials/haskell/mustache-templates/

License

Distributed under the BSD 3-clause license.