---
pagetitle: readme-lhs
---
[readme-lhs](https://tonyday567.github.io/readme-lhs/index.html) [](https://travis-ci.org/tonyday567/readme-lhs)
===
<blockquote cite>
The language in which we express our ideas has a strong influence on our thought processes. Knuth
</blockquote>
[ghc options](https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/flags.html#flag-reference)
---
> {-# OPTIONS_GHC -Wall #-}
[pragmas](https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/lang.html)
------------------------------------------------------------------------------------
> {-# LANGUAGE NoImplicitPrelude #-}
> {-# LANGUAGE OverloadedStrings #-}
> {-# LANGUAGE DataKinds #-}
> {-# LANGUAGE ScopedTypeVariables #-}
> {-# LANGUAGE TypeOperators #-}
> {-# LANGUAGE FlexibleInstances #-}
[libraries](https://www.stackage.org/)
--------------------------------------
- [protolude](https://www.hackage.org/package/protolude)
- [readme-lhs](https://www.hackage.org/package/readme-lhs)
> import Protolude
> import Readme.Lhs
code
----
- [hoogle](https://www.stackage.org/package/hoogle)
> main :: IO ()
> main = do
> let n = 10
> let answer = product [1..n::Integer]
> void $ runOutput ("example.lhs", LHS) ("readme.md", GitHubMarkdown) $ do
> output "example1" (Fence "Simple example of an output")
```{.output .example1}
```
> output "example2" (Fence (show answer))
10! is equal to:
```{.output .example2}
```
As well as fenced output, output can be Text that replaces the {.output} code block
> output "example3" (Replace "Fenced code block was overwritten")
```{.output .example3}
This will be replaced.
```
or be native pandoc.
> output "example4" (Native [BulletList [[plain "a"], [plain "bullet"], [plain "list"]]])
```{.output .example4}
```
Output that doesn't exist is simply cleared.
``` {.output .example3}
The text inside this code block will be
cleared on execution.
```
Technicals
===
This is an example of mixing literate haskell with markdown, and in using readme-lhs. The file is composed of several elements:
- literate haskell. Bird-tracks are used, as the alternative lhs method is latex. Pandoc can read this, but defaults to bird tracks when rendering `markdown+lhs`.
- markdown. All non bird-tracked lines are considered to be markdown. It's probably incompatible with haddock. This might be easily fixable.
- fenced code blocks with an output class, which are used to insert computation results. The fenced code blocks look like:
\`\`\`{.output .example}
\`\`\`
As it currently stands, ghc cannot read a file with fenced code-blocks that look like:
```
\```haskell
\```
```
Given this, a file cannot be both a valid haskell file, and a markdown file that is rendered nicely by github. This would resolve with adoption of the [literate markdown ghc proposal](https://gitlab.haskell.org/ghc/ghc/wikis/literate-markdown).
template
===
A bare bones stack template is located in [other/readme-lhs.hsfiles](other/readme-lhs.hsfiles). It contains what you need to quickly get started with literate programming.
workflow
---
```
stack build --test --exec "$(stack path --local-install-root)/bin/readme-lhs-example" --file-watch
```