transform literate source code to Markdown.
This package provides a library as well as a command-line utility that transforms literate source code to Markdown. Please see the README on GitHub at https://github.com/ExtremaIS/literatex-haskell#readme.
LiterateX
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:
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:
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:
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:
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:
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 [email protected] 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 [email protected].
License
This project is released under the MIT License as specified in the LICENSE file.