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principle-type-system-discipline SKILL.md skillA

This file is byte-identical to the first copy the registry indexed. Same content hash, so the same checks give both the same grade.

principle-type-system-discipline from iap/pstack-hermes is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.

Install it, pinned

mdr add iap/pstack-hermes/principle-type-system-discipline@git:20261031.336cc57

Pins git:20261031.336cc57 in mdr.lock. Pin the fingerprint instead.

Audit grade: A, 17 of 17 checks passed
Kind: SKILL.md skill
Repository: iap/pstack-hermes
Path: skills/principle-type-system-discipline/SKILL.md
Versions recorded: 1
Latest version: git:20261031.336cc57, committed Oct 31, 2026
Size: 4,922 bytes
Repository stars: 32
License: a license file GitHub does not identify

Apply when designing types, reviewing a function signature, or writing code in any statically-typed language. Make illegal states unrepresentable, brand semantic primitives, parse external data at boundaries, refuse to lie to the compiler, exhaust variants, derive from authoritative schemas.

Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.

What the file says

# Type System Discipline

The type checker is a proof assistant. Use it to eliminate impossible states, mismatched primitives, and unhandled variants at compile time. A case the types let you ignore becomes a runtime failure the compiler could have stopped. Prefer defining errors and special cases out of existence over proliferating handlers. Unrepresentable states, total functions, and interface redesign (the patterns below) are the tools.

Applies to any typed language. Skills like `typescript-best-practices` ground it in specific syntax.

**The patterns:**

- **Make illegal states unrepresentable.** Model variants as sum types: discriminated unions in TypeScript, enums with payloads in Rust/Swift/Kotlin, sealed classes in Scala, ADTs in Haskell/OCaml. Don't model state as a bag of optional fields where contradictory combinations compile. A subtle anti-pattern: `{ completed: boolean; completedAt?: Date }` admits `completed: true; completedAt: undefined`, which is meaningless. Derive the boolean from a single source like `completedAt !== null`, or model the variants explicitly as `{ kind: 'open' } | { kind: 'done'; at: Date }`. If a bug forces the question "wait, can this…
…

Read the whole file at its exact version.

How to install

The exact contents, by fingerprint

mdr add iap/pstack-hermes/principle-type-system-discipline@sha256:c83da8031ffb4c86

The line at the top of this page pins the label git:20261031.336cc57, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.

Badge

[![mdr](https://markdownregistry.com/badge/art_r4q2itsvi2gcjknj.svg)](https://markdownregistry.com/a/art_r4q2itsvi2gcjknj)

0 badge image fetches in 30 days. What the badge shows.

Versions

The registry has recorded 1 version of this file, committed on Oct 31, 2026.

version	committed	commit	size	audit
git:20261031.336cc57 latest	2026-10-31	336cc57	4,922 B	A	view

Audit of the latest version

A 17 of 17 checks passed. Fixed automatic checks with no AI involved, so the same checks give the same answer every run.

pass: Frontmatter block present
pass: Frontmatter declares a name
pass: Frontmatter declares a description
pass: Size between 200 bytes and 200 KB (4922 bytes)
pass: No zero-width or bidi control characters
pass: No instruction hidden inside an HTML comment
pass: No link to an exfiltration or paste host
pass: No credential-shaped string
pass: No instruction to send local credentials anywhere
pass: No text hidden with inline styles
pass: No prompt-injection phrasing
pass: No curl or wget piped into a shell
pass: No recursive delete of root, home or parent
pass: No instruction to read or print local credentials
pass: No base64 blob over 200 characters
pass: No link to a raw IP address
pass: No script tag

Source

GitHub

iap/pstack-hermes · 32 stars · license a license file GitHub does not identify · pushed 2026-11-04 · branch master

API

GET https://markdownregistry.com/api/v1/artifacts/art_r4q2itsvi2gcjknj
GET https://markdownregistry.com/api/v1/resolve?ref=iap/pstack-hermes/principle-type-system-discipline
GET https://markdownregistry.com/api/v1/blob/c83da8031ffb4c86410030d3e261f659598fca2b7d8158fd9dc269d70a3a025e

Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.

Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.

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