Blog.hs

Path: build/Blog.hs | Language: Haskell | Lines: ~274

Generates standalone blog pages from authored annotations and directory indexes

Overview

Blog.hs addresses a design problem in gwern.net: how to publish "small" or "one-off" writings without the overhead of creating full top-level essays. The traditional essay format requires extensive metadata, formatting, a stable URL, and ongoing maintenance—but many popular writings originated as quick comments on LessWrong, Hacker News, or Reddit.

The solution leverages the annotation system. Off-site writings get saved as annotations with a custom ID (e.g., gwern-2025-drl-scaling), and this module automatically generates a standalone page at /blog/2025/drl-scaling that transcludes that annotation. This gives blog posts the benefits of both systems: lightweight authoring via annotations, but with stable URLs, discoverability through /blog/index, and the ability to be promoted to full essays later.

The module generates three outputs: individual blog post pages (/blog/YYYY/slug.md), a full directory index (/blog/index.md), and a simplified recent-posts list (/blog/newest.md) intended for homepage transclusion.

Public API

`writeOutBlogEntries :: Metadata -> IO ()`

Main entry point. Filters the annotation database for authored writings, validates them, generates individual blog post files, and creates the index pages.

Called by: hakyll.hs (line 79, during site build initialization) Calls: filterForAuthoredAnnotations, writeOutBlogEntry, generateDirectoryBlog, generateDirectoryBlogSimplified, metadataItem2ID (from LinkID)

Internal Architecture

Data Flow

Metadata (annotation DB)
    │
    ▼
filterForAuthoredAnnotations  ─► Filter by author="Gwern" + length>600
    │
    ▼
Validation Pipeline:
  - Check for overly long posts (>30k chars) → warning
  - Validate dates (must be 10 chars: YYYY-MM-DD)
  - Validate titles (max 51 chars for mobile)
  - Validate IDs (checkIdent)
    │
    ▼
Path Generation:
  ID "gwern-2025-foo" → "blog/2025/foo.md"
    │
    ▼
┌─────────────────────────────────────────┐
│ For each entry:                         │
│   writeOutBlogEntry → blog/YYYY/slug.md │
│                                         │
│ generateDirectoryBlog → blog/index.md   │
│ generateDirectoryBlogSimplified →       │
│                       blog/newest.md    │
└─────────────────────────────────────────┘

Key Functions

filterForAuthoredAnnotations :: Metadata -> MetadataList

Filters annotations to find blog candidates:

URL must not be local OR must already be under /blog/
Author must start with "Gwern Branwen"
Abstract must exceed lengthMin (600 characters)

checkIdent :: String -> Bool

Validates ID format. Expects gwern-YYYY/slug or gwern-YYYY-slug:

Minimum length: 13 characters (gwern-YYYY?s)
Maximum length: 47 characters
Year must be 2009 through current year
Slug: alphanumeric and hyphens only

annotation2Markdown :: Path -> MetadataItem -> String

Generates the Markdown content for a blog post page. Creates YAML frontmatter from annotation metadata, then a single transclusion directive:

---
title: 'Title Here'
author: Gwern Branwen
description: "..."
created: YYYY-MM-DD
modified: YYYY-MM-DD
status: finished
...

[Description](https://original-url.com){.include-annotation ...}

<div class='text-center' id='return-to-blog-index-link'>...</div>

Key metadata fields extracted from annotation key-value pairs:

description, status, importance, confidence
css-extension (defaults to dropcaps-de-zs toc-not)
thumbnail, thumbnail-text

generateDirectoryBlog :: [(FilePath, Path, MetadataItem)] -> IO ()

Creates /blog/index.md with:

Link sections by year - Bulleted lists of blog post links grouped by year
Transclude sections - Full annotation transclusions for reading without clicking

Uses Pandoc AST to generate Markdown. Current/last year sections get special IDs (year-current, year-last) for CSS styling.

generateDirectoryBlogSimplified :: [(FilePath, Path, MetadataItem)] -> IO ()

Creates /blog/newest.md with the 29 most recent posts in a two-column bulleted list. Intended for transclusion onto the homepage.

Key Patterns

Recursive Blog Posts

A clever design feature: since the system generates blog pages from annotations, you can create a "recursive" blog post by writing an annotation for a /blog/YYYY/foo URL. The annotation creates the page, which transcludes itself. This allows true standalone blog content rather than requiring an external source URL.

ID Format Flexibility

The system accepts two ID formats and normalizes them:

gwern-2025/foo (slash separator)
gwern-2025-foo (hyphen separator)

Both become blog/2025/foo.md. This accommodates different annotation ID conventions.

Transclusion Classes

Blog post pages use specific transclusion classes:

.include-annotation - Triggers annotation system
.include-strict - Strict mode (fail if missing)
data-include-template='annotation-blockquote-not' - Custom template
.include-spinner-not - No loading spinner
.id-not - Don't generate automatic ID

For non-local URLs, adds rel='canonical' to indicate the original source.

Configuration

Constants (hardcoded in module)

Constant	Value	Purpose
`prefix`	`"blog"`	Output directory prefix
`authorU`	`"Gwern Branwen"`	Full author name for filtering
`authorID`	`"gwern"`	ID prefix for annotations
`lengthMin`	600	Minimum abstract length to qualify
`lengthMax`	30000	Warning threshold for long posts
`titleMax`	51	Title length for mobile display

From Config.Misc

C.cd - Changes to site root directory
C.currentYear / C.currentYearS - For year validation
C.lastYearS - For CSS class assignment
C.author / C.authorL - Author name variants

Integration Points

Input Dependencies

LinkMetadata - sortByDatePublished for chronological ordering
LinkMetadataTypes - Metadata, MetadataList, MetadataItem, Path types
LinkID - metadataItem2ID extracts the custom ID from annotations
Metadata.Date - isYear validates year strings
Typography - titlecase' for title formatting

Output Files

File	Purpose
`blog/YYYY/slug.md`	Individual blog post pages
`blog/index.md`	Full directory with links + transclusions
`blog/newest.md`	Recent posts for homepage

Build Integration

Called early in hakyll.hs build process (line 79), before main Hakyll compilation. Uses writeUpdatedFile to only write files when content changes (avoiding unnecessary rebuilds).

Validation & Error Handling

The module is strict about data quality:

Empty results - Errors if no blog posts found
Long posts - Warning (not error) for posts >30k chars
Invalid dates - Error if not exactly 10 characters
Long titles - Warning for titles >51 chars
Invalid IDs - Error with details about expected format
Path uniqueness - Uses isUniqueList to detect duplicate paths
Year validation - Must be 2009 through current year

Error messages include the specific offending entries for debugging.

Overview​

Public API​

writeOutBlogEntries :: Metadata -> IO ()​

Internal Architecture​

Data Flow​

Key Functions​

Key Patterns​

Recursive Blog Posts​

ID Format Flexibility​

Transclusion Classes​

Configuration​

Constants (hardcoded in module)​

From Config.Misc​

Integration Points​

Input Dependencies​

Output Files​

Build Integration​

Validation & Error Handling​

See Also​