Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add rules/pauljphilp/effectpatterns/comparing-data-by-value-with-datastructgit clone --depth 1 https://github.com/PaulJPhilp/EffectPatternsWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00286 | $0.00286 |
| Opus 5 | $0.00143 | $0.00143 |
| Sonnet 5 | $0.00057 | $0.00057 |
| Haiku 4.5 | $0.00029 | $0.00029 |
Grade A, and why
comparing-data-by-value-with-datastruct scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
What it actually says
description: Use Data.struct to define objects whose equality is based on their contents, enabling safe and predictable comparisons. globs: "**/*.ts" alwaysApply: true
Comparing Data by Value with Data.struct
Rule: Use Data.struct to define objects whose equality is based on their contents, enabling safe and predictable comparisons.
Example
import { Data, Equal } from "effect";
// Create two structurally equal objects
const user1 = Data.struct({ id: 1, name: "Alice" });
const user2 = Data.struct({ id: 1, name: "Alice" });
// Compare by value, not reference
const areEqual = Equal.equals(user1, user2); // true
// Use in a HashSet or as keys in a Map
import { HashSet } from "effect";
const set = HashSet.make(user1);
console.log(HashSet.has(set, user2)); // true
Explanation:
Data.structcreates immutable objects with value-based equality.- Use for domain entities, value objects, and when storing objects in sets or as map keys.
- Avoids bugs from reference-based comparison.
Explanation:
JavaScript objects are compared by reference, which can lead to subtle bugs when modeling value objects.
Data.struct ensures that two objects with the same contents are considered equal, supporting value-based logic and collections.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 2d ago First seen · 34 lines · 286 tokens per session scan A a2e772801ca4
comparing-data-by-value-with-datastruct is a cursor rule published in the GitHub repository PaulJPhilp/EffectPatterns (795 stars, last pushed 2mo ago), licensed MIT. It adds 286 tokens to every session, about $0.0014 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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