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GHC 9.10.3 · lts/ghc-9.10.x · c74966e · 2026-09-27

Modulemicrostache-1.0.3Haskell2010

Text.Microstache

This is a Haskell implementation of Mustache templates. The implementation conforms to the version 1.1.3 of official Mustache specification https://github.com/mustache/spec. It is extremely simple and straightforward to use with minimal but complete API — three functions to compile templates (from directory, from file, and from lazy text) and one to render them.

For rendering you only need to create Aeson's Data.Aeson.Value where you put the data to interpolate. Since the library re-uses Aeson's instances and most data types in Haskell ecosystem are instances of classes like Data.Aeson.ToJSON, the whole process is very simple for the end user.

Template Haskell helpers for compilation of templates at compile time are available in the Text.Microstache.Compile.TH module. The helpers are currently available only for GHC 8 users though.

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 parsed template representation. The decision to drop lambdas is intentional, for the sake of simplicity and better integration with Aeson.

Here is an example of basic usage:

{-# LANGUAGE OverloadedStrings #-}

module Main (main) where

import Data.Aeson
import Data.Text
import Text.Microstache
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 err -> print err
    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:

  • 6 types
  • 7 values
  • Packagemicrostache-1.0.3
  • Exports13
  • LanguageHaskell2010
  • LicenceBSD-3-Clause
  • SourceMicrostache.hs

Types

8 declarations
datadata Template
#

Mustache template as name of “top-level” template and a collection of all available templates (partials).

Template is a Semigroup. This means that you can combine Templates (and their caches) using the (<>) operator, the resulting Template will have the same currently selected template as the left one. Union of caches is also left-biased.

Constructors

Instances7Eq, Data, Ord, Show, Generic, Semigroup, …
datadata Node
#

Structural element of template.

Constructors

Instances6Eq, Data, Ord, Show, Generic, Rep
newtypenewtype Key
#

Identifier for values to interpolate.

The representation is the following:

  • [] — empty list means implicit iterators;

  • [text] — single key is a normal identifier;

  • [text1, text2] — multiple keys represent dotted names.

Constructors

Instances9Eq, Data, Ord, Show, Generic, Semigroup, …
newtypenewtype PName
#

Identifier for partials. Note that with the OverloadedStrings extension you can use just string literals to create values of this type.

Constructors

Instances8Eq, Data, Ord, Show, IsString, Generic, …
datadata MustacheException
#

Exception that is thrown when parsing of a template has failed or referenced values were not provided.

Constructors

Instances5Eq, Show, Generic, Exception, Rep
datadata MustacheWarning
#

Constructors

Instances5Eq, Show, Generic, Exception, Rep

Compiling

3 declarations
valuecompileMustacheDir
  1. :: PName

    Which template to select after compiling

  2. -> FilePath

    Directory with templates

  3. -> IO Template

    The resulting template

#

Compile all templates in specified directory and select one. Template files should have extension mustache, (e.g. foo.mustache) to be recognized. This function does not scan the directory recursively.

The action can throw the same exceptions as getDirectoryContents, and T.readFile.

Rendering

2 declarations