IdeaWell

Project ideas from Hacker News discussions.

Dates That Don't Exist (2015)

Original Article

Hacker News Discussion

📝 Discussion Summary (Click to expand)

1. Libraries treat dates as proleptic Gregorian

"A date object represents a date (year, month and day) in an idealized calendar, the current Gregorian calendar indefinitely extended in both directions." — flotzam

2. Calendar gaps create “impossible” dates that must be handled

"I assume there is a way to handle this in modern contract law. Surely people have forgotten how long the various months are and written contracts referring to April 31." — madcaptenor

3. Calendar adoption varied by region, so multiple systems coexisted

"Technically, they switched to the Revised Julian calendar, not the Gregorian. Also, it was only some of the churches making up Eastern Orthodoxy that switched; others remain on the Julian calendar to this day..." — jaculabilis

🚀 Project Ideas

Generating project ideas…

Proleptic Date Validator SDK

Summary

  • Detects and flags dates that fall within impossible “gap” periods (e.g., 5‑14 Oct 1582) and inconsistent historical calendar usage.
  • Provides safe conversion helpers to map such dates to the correct proleptic calendar for legal, database, or financial use cases.

Details

Key Value
Target Audience Game developers, fintech, legal‑tech, and any systems handling historical dates or contracts
Core Feature Automatic detection of non‑existent dates, configurable jurisdiction rules, and conversion to proleptic Gregorian/Julian
Tech Stack Rust (for speed), WASM for browser use, PostgreSQL for persistence, OpenAPI spec
Difficulty Medium
Monetization Revenue-ready: subscription tier for API calls

Notes

  • HN commenters repeatedly noted “I tried to create a date object in Swift from the date October 5, 1582… it became October 15th” and discussed legal contracts needing gap awareness.
  • Provides a clear, programmatic answer to “how do I handle dates that never existed?” – a direct pain point.
  • Could be packaged as a micro‑library or SaaS validation endpoint, encouraging community contributions and paid premium features.

Contract Clause Calendar Gap Checker

Summary

  • Scans contract documents for dates in the 1582 calendar gap or in jurisdictions with later adoption (e.g., Britain 1752, Russia 1918).
  • Auto‑suggests proper date formatting, jurisdiction‑specific disclosures, and validation rules to avoid ambiguous “Dubia” clauses.

Details

Key Value
Target Audience Legal tech platforms, contract‑management SaaS, corporate legal departments
Core Feature Text‑analysis engine that highlights flagged dates, outputs a “gap‑risk” score, and proposes compliance language
Tech Stack Python (NLTK/Spacy), Elasticsearch for indexing, Flask REST API, Docker deployment
Difficulty High
Monetization Revenue-ready: license per user seat (annual)

Notes

  • Directly references bombcar’s comment about drafting a Dubia for future papal calendar changes and wongarsu’s concern about payment deadlines.
  • Addresses the practical need of ensuring contracts are legally sound when dates fall on non‑existent days.
  • Integration with existing contract‑review pipelines offers immediate utility and a clear path to monetization.

Historical Calendar Converter CLI

Summary

  • Command‑line tool that takes any date, determines the applicable calendar (Julian, Proleptic Gregorian, Revised Julian, etc.), and reports day‑count differences, leap‑day handling, and era switches.
  • Includes utilities for batch processing, CSV import/export, and interactive mode for historians or developers.

Details

Key Value
Target Audience Historians, genealogists, open‑source enthusiasts, data‑engineers working with legacy datasets
Core Feature Bulk conversion of dates across multiple calendar systems, day‑range analysis spanning reform periods, JSON output for pipelines
Tech Stack Go (standard library), Cobra CLI, SQLite for internal reference data, GitHub Actions CI
Difficulty Low
Monetization Hobby

Notes

  • Several commenters (e.g., matsemann, 1313ed01) asked about day‑of‑month jumps and Swedish February 30, indicating a demand for precise date arithmetic.
  • Provides a technical answer to “does the day‑of‑month accurately jump over the non‑existent numbers?” – a direct pain point.
  • Open‑source utility can gain traction on HN, Spark discussions on calendar handling, and potential paid extensions for enterprise support.

Read Later