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.
git clone --depth 1 https://github.com/PaulJPhilp/EffectPatternsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/rules/pauljphilp/effectpatterns/effectful-pattern-matching-with-matcheffect)<a href="https://agentmods.dev/rules/pauljphilp/effectpatterns/effectful-pattern-matching-with-matcheffect"><img src="https://agentmods.dev/badge/rules/pauljphilp/effectpatterns/effectful-pattern-matching-with-matcheffect.svg" alt="Measured on agentmods" height="20"></a>What 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 5.1 | $0.00250 | $0.00250 |
| Opus 5 | $0.00125 | $0.00125 |
| Sonnet 5 | $0.00050 | $0.00050 |
| Haiku 4.5 | $0.00025 | $0.00025 |
Grade A, and why
effectful-pattern-matching-with-matcheffect 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 4d 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 matchEffect to pattern match on the result of an Effect, running effectful logic for both success and failure cases. globs: "**/*.ts" alwaysApply: true
Effectful Pattern Matching with matchEffect
Rule: Use matchEffect to pattern match on the result of an Effect, running effectful logic for both success and failure cases.
Example
import { Effect } from "effect";
// Effect: Run different Effects on success or failure
const effect = Effect.fail("Oops!").pipe(
Effect.matchEffect({
onFailure: (err) => Effect.logError(`Error: ${err}`),
onSuccess: (value) => Effect.log(`Success: ${value}`),
})
); // Effect<void>
Explanation:
matchEffectallows you to run an Effect for both the success and failure cases.- This is useful for logging, cleanup, retries, or any effectful side effect that depends on the outcome.
Explanation:
Sometimes, handling a success or failure requires running additional Effects (e.g., logging, retries, cleanup).
matchEffect lets you do this declaratively, keeping your code composable and type-safe.
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.
- 4d ago First seen · 29 lines · 250 tokens per session scan A 3cc72a7c54f1
effectful-pattern-matching-with-matcheffect is a cursor rule published in the GitHub repository PaulJPhilp/EffectPatterns (796 stars, last pushed 2mo ago), licensed MIT. It adds 250 tokens to every session, about $0.0013 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 2026-09-03.
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