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haskell-expert

haskell-expert is a skill for Claude Code from personamanagmentlayer/pcl. It costs 79 tokens per session (1,401 once invoked), scanned A, original, Apache-2.0.

A Haskell programming reference skill covering functional programming, strong type systems, lazy evaluation, and monads. Haskell is a programming language that commonly uses immutable data and functions without side effects.

In plain words
What is it for?
It helps explain or work with pure functions, type classes, pattern matching, lazy evaluation, recursion, monads, and advanced Haskell types.
Why use it?
It supplies language-specific guidance for concepts that may be unfamiliar or difficult to apply correctly in Haskell code.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

not rated 45repo +1 18d ago A scan SkillSpector: pass 79 tokens original Apache-2.0

Good fit It helps explain or work with pure functions, type classes, pattern matching, lazy evaluation, recursion, monads, and advanced Haskell types.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/personamanagmentlayer/pcl/haskell-expert
View source ↗ personamanagmentlayer/pcl pclang.org
Install

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.

Any agent
npx skills add personamanagmentlayer/pcl --skill haskell-expert
Clone the repo
git clone --depth 1 https://github.com/personamanagmentlayer/pcl

Made for: Claude Code.

Wrote 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.

agentmods badge for haskell-expert

README.md
[![agentmods](https://agentmods.dev/badge/skills/personamanagmentlayer/pcl/haskell-expert/github.svg)](https://agentmods.dev/skills/personamanagmentlayer/pcl/haskell-expert)
Your own site
<a href="https://agentmods.dev/skills/personamanagmentlayer/pcl/haskell-expert"><img src="https://agentmods.dev/badge/skills/personamanagmentlayer/pcl/haskell-expert/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for haskell-expert

Your own site · 80×15
<a href="https://agentmods.dev/skills/personamanagmentlayer/pcl/haskell-expert"><img src="https://agentmods.dev/badge/skills/personamanagmentlayer/pcl/haskell-expert.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 79 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,401 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00079 $0.01401
Opus 5.5 $0.00032 $0.00560
Sonnet 5.5 $0.00016 $0.00280
Haiku 4.5 $0.00008 $0.00140

Measured 2mo ago against content hash 5f847c4a8384, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

haskell-expert 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 2mo 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.

stdlib/languages/haskell-expert/SKILL.md · 200 lines

How it starts

The opening of the file, as written. The whole thing — 200 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Haskell Expert

You are an expert in Haskell programming language, specializing in functional programming, advanced type systems, monads, type classes, and purely functional design patterns.

Core Concepts

Functional Programming

  • Pure Functions: No side effects, referential transparency
  • Immutability: All values are immutable by default
  • Higher-Order Functions: Functions as first-class values
  • Composition: Build complex functions from simple ones
  • Recursion: Primary iteration mechanism
  • Pattern Matching: Destructure data elegantly

Type System

  • Strong Static Typing: Compile-time type safety
  • Type Inference: Hindley-Milner type inference
  • Parametric Polymorphism: Generic types
  • Type Classes: Ad-hoc polymorphism
  • GADTs: Generalized Algebraic Data Types
  • Type Families: Type-level functions

Lazy Evaluation

  • Non-Strict Semantics: Expressions evaluated when needed
  • Infinite Data Structures: Define infinite lists
  • Thunks: Suspended computations
  • Strictness Annotations: Control evaluation strategy
  • Space Leaks: Understanding and preventing
  • Fusion: Automatic optimization of compositions

Monads and Effects

  • Monad Type Class: Abstract computation patterns
  • IO Monad: Handle side effects purely
  • Maybe/Either: Error handling monads
  • State Monad: Stateful computations
  • Reader/Writer: Environment and logging
  • Monad Transformers: Compose monadic effects

Best Practices

Function Design

  • Keep functions pure when possible
  • Use descriptive type signatures
  • Leverage higher-order functions
  • Compose small functions into larger ones
  • Use point-free style judiciously
  • Prefer pattern matching over if-then-else

Type System

  • Let type inference work for you
  • Add type signatures for top-level functions
  • Use newtype for type safety
  • Leverage type classes for polymorphism
  • Use GADTs for type-safe DSLs
  • Consider phantom types for compile-time guarantees

Read the full file on GitHub · 200 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

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.

  1. 2mo ago First seen · 200 lines · 79 tokens per session scan A 5f847c4a8384

Subscribe to this mod's changes

haskell-expert is a skill published in the GitHub repository personamanagmentlayer/pcl (45 stars, last pushed 18d ago), licensed Apache-2.0. It adds 79 tokens to every session and 1,401 once invoked, about $0.0003 per session on Opus 5.5. 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 2026-09-05.

Languagesanthropiccategory-theoryclaudedeepseekfunctional-programminggeminihaskelllazy-evaluationmonadspure-functionstype-system
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