About

Imported from personamanagmentlayer/pcl (stdlib/languages/haskell-expert/SKILL.md). Install upstream with npx skills add personamanagmentlayer/pcl --skill haskell-expert. Copyright stays with the author.

Haskell Expert

Name: haskell-expert
Author: personamanagmentlayer

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

Lazy Evaluation

Understand when evaluation happens
Use strict folds (foldl') for accumulation
Apply strictness annotations when needed
Watch for space leaks
Profile before optimizing
Leverage laziness for infinite structures

Monad Usage

Choose appropriate monads for effects
Use do-notation for readability
Consider monad transformers for multiple effects
Keep monadic code isolated
Understand monad laws
Use liftIO sparingly in transformers

Code Organization

One module per logical component
Export only necessary functions
Use qualified imports to avoid conflicts
Group related functions
Document with Haddock comments
Follow Haskell naming conventions

Anti-Patterns

Performance Issues

Using foldl instead of foldl'
Creating unnecessary space leaks
Not profiling before optimizing
Overusing lazy evaluation
Ignoring strictness analysis
Premature abstraction

Type System Misuse

Overcomplicating with advanced features
Not using type signatures
Avoiding newtype wrappers
Overusing String instead of Text
Type class proliferation
Partial functions without Maybe/Either

Monad Misuse

Excessive monad transformer stacks
Using IO for everything
Not understanding monad laws
Mixing effects unnecessarily
Overusing unsafePerformIO
Not leveraging monad properties

Code Quality

Partial functions (head, tail, !!)
Ignoring compiler warnings
Not handling errors properly
Overusing lazy I/O
Poor naming conventions
Insufficient testing

General Anti-Patterns

Fighting the type system
Premature optimization
Not using standard libraries
Reinventing the wheel
Overly clever code
Neglecting documentation

Reference Documentation

Detailed material lives alongside this skill and is read on demand:

Code Examples — Installation and Setup, Functional Programming Basics, Algebraic Data Types and Type Classes, Monads and Effect Handling, Advanced Type System Features, Lazy Evaluation and Performance

Resources

Official Documentation

Learning Resources

Advanced Topics

Tools and Libraries

Hoogle - API search
Stackage - Stable package sets
HLS - Language server

Community

Use it

Copy one of these into your project. Installing also returns the manifest and these snippets.

yaml

targets:
  - https://api.opensmartroute.ai/api/v1/registry/personamanagmentlayer-pcl-haskell-expert/manifest   # or paste the manifest below

Manifest

An Open Capability Manifest: the router reads it to know what this does, what it costs and when to pick it.

personamanagmentlayer-pcl-haskell-expert.ocm.jsonjson

{
  "ocm": "1",
  "id": "personamanagmentlayer-pcl-haskell-expert",
  "kind": "skill",
  "name": "haskell-expert",
  "description": "Expert knowledge in Haskell functional programming, advanced type system, monads, lazy evaluation, and purely functional design. Use when the user mentions functional programming, monads, type system, lazy evaluation, pure functions, or category theory, or when the task involves Monads and Effects, Installation and Setup, Functional Programming Basics, or Algebraic Data Types and Type Classes.",
  "publisher": "personamanagmentlayer",
  "version": "1.0.0",
  "capabilities": {
    "domains": [
      "general"
    ],
    "tags": [
      "skill-md",
      "haskell",
      "functional-programming",
      "monads",
      "type-system",
      "lazy-evaluation",
      "pure-functions",
      "category-theory",
      "skills-sh"
    ],
    "languages": [
      "en"
    ]
  },
  "quality_prior": 0.6,
  "examples": [
    "Expert knowledge in Haskell functional programming, advanced type system, monads, lazy evaluation, and purely functional design. Use when the user mentions functional programming, monads, type system, lazy evaluation, pure functions, or category theory, or when the task involves Monads and Effects, Installation and Setup, Functional Programming Basics, or Algebraic Data Types and Type Classes."
  ],
  "primary": false,
  "metadata": {
    "source": {
      "provider": "skills.sh",
      "repository": "https://github.com/personamanagmentlayer/pcl",
      "path": "stdlib/languages/haskell-expert/SKILL.md",
      "ref": "HEAD",
      "url": "https://github.com/personamanagmentlayer/pcl/blob/HEAD/stdlib/languages/haskell-expert/SKILL.md",
      "key": "personamanagmentlayer/pcl/stdlib/languages/haskell-expert/SKILL.md"
    },
    "allowed_tools": [
      "Read",
      "Write",
      "Edit",
      "Bash",
      "Glob",
      "Grep"
    ]
  },
  "instructions": "# Haskell Expert\n\nYou are an expert in Haskell programming language, specializing in functional programming, advanced type systems, monads, type classes, and purely functional design patterns.\n\n## Core Concepts\n\n### Functional Programming\n\n- **Pure Functions**: No side effects, referential transparency\n- **Immutability**: All values are immutable by default\n- **Higher-Order Functions**: Functions as first-class values\n- **Composition**: Build complex functions from simple ones\n- **Recursion**: Primary iteration mechanism\n- **Pattern Matching**: Destructure data elegantly\n\n### Type System\n\n- **",
  "cost": {
    "context_tokens": 1341
  }
}

Fetch it by URL: GET /api/v1/registry/personamanagmentlayer-pcl-haskell-expert/manifest?version=1.0.0

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