LiterateX

• Overview
• Source Formats
  • Double-Dash Comments
  • Double-Slash Comments
  • Hash Comments
  • Lisp Semicolon Comments
  • Literate Haskell
  • Percent Comments
• CLI
  • Requirements
  • Installation
    • .deb Package Installation
    • .rpm Package Installation
    • Installation From Hackage
    • Installation From Stackage
  • Usage
• Library
• Related Work
• Project
  • Links
  • Tags
  • Contribution
  • License

Overview

LiterateX transforms literate source code to Markdown. Write documentation in Markdown format in the comments of source code, and LiterateX can transform the file to Markdown, optionally including the source code with syntax highlighting and line numbers. Many source formats are supported, and the following target formats are supported:

• Pandoc Markdown
• GitHub Flavored Markdown
• mdBook Markdown, which does not support per-block line numbering

LiterateX can be used to document code that is particularly important or difficult to understand. For example, documentation can be written in the SQL file that defines the schema for a complex database. LiterateX can translate the .sql file to a Markdown file, which can then be converted to HTML, PDF, or even EPUB with Pandoc.

LiterateX can also be used in the publishing of blog entries, magazine articles, or books. Use the command-line utility or integrate the Haskell library into your own software.

LiterateX has support for source code rules, comment lines that are used to visually separate sections of source code. Since source code rules are only used to make the source code easier to scan quickly, they are ignored (treated as a blank line) when translating to Markdown.

LiterateX also has support for shebang lines at the start of the file. They can be ignored so that they do not precede the documentation.

Source Formats

LiterateX supports a number of source formats. With the exception of literate Haskell, documentation is written in line comments in the source language. Note that multi-line comments are treated as code, not documentation.

Double-Dash Comments

Documentation is parsed from lines that begin with two dashes immediately followed by a space (-- ). Lines that only contain two dashes are treated as blank lines in the documentation. Lines that contain three or more dashes are treated as source code rules and are ignored.

-- # Haskell Example
--
-- Executables are implemented using a `Main` module that exposes a function
-- named `main`.

module Main (main) where

-- The `main` function is run when the program is executed.

main :: IO ()
main = putStrLn "Hello!"

-- This simple example just prints "Hello!" to the screen.

Languages that use double-dash comments include the following:

• Elm
• Haskell
• Idris
• Lua
• SQL

Double-Slash Comments

Documentation is parsed from lines that begin with two slashes immediately followed by a space (// ). Lines that only contain two slashes are treated as blank lines in the documentation. Lines that contain three or more slashes are treated as source code rules and are ignored.

// # Rust Example
//
// The `main` function is run when the program is executed.

fn main() {
    println!("Hello!");
}

// This simple example just prints "Hello!" to the screen.

Languages that use double-slash comments include the following:

• C
• CSS
• Go
• Java
• JavaScript
• Kotlin
• PHP
• Rust
• Scala
• TypeScript

Hash Comments

Documentation is parsed from lines that begin with a hash character immediately followed by a space (# ). Lines that only contain a hash character are treated as blank lines in the documentation. Lines that contain two or more hash characters are treated as source code rules and are ignored.

# # Python Example
#
# A quick-and-dirty Python script can include commands at the top level!

print("Hello!")

# This simple example just prints "Hello!" to the screen.

Languages that use hash comments include the following:

• Bash
• Elixir
• Perl
• Python
• R
• Ruby

Lisp Semicolon Comments

Lisp languages use a semicolon (;) for line comments, but there is a special convention to use a different number of semicolons according to the context. Documentation is parsed from lines that begin with one to four semicolons immediately followed by a space (; , ;; , ;;; , or ;;;; ). Lines that only contain one to four semicolons are treated as blank lines in the documentation. Lines that contain more than four semicolons are treated as source code rules and are ignored.

; # Racket Example
;
; Racket programs must declare the language to use.

#lang racket/base

; Racket can also include commands at the top level!

(println "Hello!")

; This simple example just prints "Hello!" to the screen.

Languages that use Lisp semicolon comments include the following:

• Clojure
• Common Lisp
• Racket
• Scheme

Literate Haskell

GHC has special support for literate programming. Haskell source code is usually written with documentation in comments, in files with a .hs extension. Literate Haskell source code gives documentation the leading role and prefixes code with a greater-than sign and space (> ), in files with a .lhs extension. The documentation can be in any format, and Markdown is a popular choice.

Unfortunately, there is a bug that causes problems when using ATX-style headings (# characters before the heading text). Any easy workaround is to use setext-style headings (underlines) instead, but this limits the number of heading levels. See the Literate Haskell Markdown Headings blog post for more information and an example workaround.

This source format does not support source code rules.

Literate Haskell Example
========================

Executables are implemented using a `Main` module that exposes a function
named `main`.

> module Main (main) where

The `main` function is run when the program is executed.

> main :: IO ()
> main = putStrLn "Hello!"

This simple example just prints "Hello!" to the screen.

Percent Comments

Documentation is parsed from lines that begin with a percent character immediately followed by a space (% ). Lines that only contain a percent character are treated as blank lines in the documentation. Lines that contain two or more percent characters are treated as source code rules and are ignored.

% # Erlang Example
%
% Programs are implemented using a `main` module that exports a `start/0`
% function.

-module(main).
-export([start/0]).

% The `start` function is run when the program is executed.

start() -> io.fwrite("Hello!\n").

% This simple example just prints "Hello!" to the screen.

Languages that use percent comments include the following:

• Erlang
• LaTeX

CLI

LiterateX may be used via a command-line utility named literatex.

Requirements

literatex has only been tested on Linux. It might work on Windows and macOS.

Installation

.deb Package Installation

Check the Releases page for .deb packages.

.rpm Package Installation

Check the Releases page for .rpm packages.

Installation From Hackage

Install literatex from Hackage using Cabal as follows:

$ cabal v2-install literatex

Installation From Stackage

Install literatex from Stackage using Stack as follows:

$ stack install literatex

Usage

See the literatex man page for usage information.

Library

The LiterateX Haskell library provides an API for integrating LiterateX functionality in your own software.

Related Work

Literate programming is a style of programming introduced by Donald Knuth in which the main idea is "to regard a program as a communication to human beings rather than as a set of instructions to a computer." LiterateX is faithful to this idea in that it is used for communication to human beings. Note, however, that LiterateX does not support another core aspect of Knuth's literate programming: the ability to write source code in the order best for human understanding. Since LiterateX transforms actual source code files, the source code has to be written in whatever order is required by the language. Those interested in writing code in different order are encouraged to check out noweb and CWEB.

The lhs2tex utility is used to work with literate Haskell and LaTeX.

The markdown-unlit utility is used to extract Haskell code from Markdown files. This is useful in cases where the Markdown file is displayed on GitHub.

The src2md utility, written in Common Lisp, also supports multiple source formats. It outputs Markdown that includes HTML, which limits the usefulness of the Markdown.

The extract-documentation-comments utility, written in JavaScript, extracts documentation from multi-line JavaScript comments.

mlp.clj, written in Clojure, is a babashka script that transforms literate Clojure source code to Markdown, including HTML. The author uses it to implement a live preview of literate Clojure documentation while using the Notepad++ (Windows editor).

Project

Links

• Hackage: https://hackage.haskell.org/package/literatex
• Stackage: https://www.stackage.org/package/literatex
• Flora: https://flora.pm/packages/@hackage/literatex
• GitHub: https://github.com/ExtremaIS/literatex-haskell
• GitHub Actions CI: https://github.com/ExtremaIS/literatex-haskell/actions

Branches

The main branch is reserved for releases. It may be considered stable, and HEAD is always the latest release.

The develop branch is the primary development branch. It contains changes that have not yet been released, and it is not necessarily stable.

Hackage revisions are made for metadata changes, such as relaxation of constraints when new versions of dependencies are released. The literatex.cabal metadata in the main branch may therefore not match that of Hackage. The literatex.cabal metadata in the develop branch may match, unless work is being done on a new release that contains other changes.

Tags

All releases are tagged in the main branch. Release tags are signed using the security@extrema.is GPG key.

Contribution

Issues and feature requests are tracked on GitHub: https://github.com/ExtremaIS/literatex-haskell/issues

Issues may also be submitted via email to bugs@extrema.is.

License

This project is released under the MIT License as specified in the LICENSE file.