markdown-hs

A small Haskell project that converts a subset of Markdown into HTML.

This started as a learning project to practice core Haskell concepts — pattern matching, recursion, Maybe-based error handling, and simple recursive parsing — by building something practical from scratch.

Features

• Headings (# to ######)
• Bold text (**text**)
• Italic text (*text*)
• Unordered lists (- item), including nested lists (2 spaces of indentation per level)
• Horizontal rules (--- or ***)
• Inline Code (Text with `code` in it)
• Fenced Code Block (Start/End Block with ``` )

Anything that doesn't match a supported pattern is marked with an HTML comment (<!-- Error: invalid line -->) instead of failing silently.

Requirements

• GHC (tested with GHC 9.10.3)

Build

ghc -Wall -outputdir build -o convert .\Main.hs  

Usage

./convert

The program reads from input.md and writes the converted HTML to output.html in the current directory.

See example.md for a sample input file covering all supported features — copy it to input.md to try it out:

cp example.md input.md
./convert

Limitations

This is a learning project, not a full Markdown implementation. Notably missing: links, ordered lists, and blockquotes.

Behavior worth knowing:

• Every non-empty line becomes its own paragraph; empty lines only separate blocks and produce no output.
• A blank line ends a list, so two lists separated by an empty line are rendered as two separate lists.
• A line with only the marker (- or - ) is not a list item and is rendered as a paragraph.
• Nesting is based on indentation: one level per two leading spaces.

Documentation

The functions are documented with Haddock comments. To generate the HTML documentation into docs/ (ignored by git):

haddock --html -o docs Main.hs BlockProcessing.hs LineParsing.hs InlineFormatting.hs Validation.hs StringUtils.hs TagHelpers.hs Config.hs

Project structure

• Main.hs — entry point: reads the input file and chains the processing steps
• BlockProcessing.hs — block-level handling (code blocks, horizontal rules, lists)
• LineParsing.hs — single-line parsing (headings, paragraphs, list content)
• InlineFormatting.hs — inline formatting (bold, italic, inline code)
• Validation.hs — checks for headings and list items, list nesting level
• StringUtils.hs — string helper functions
• TagHelpers.hs — HTML tag helpers
• Config.hs — file path configuration