hoogle - SKILL.md Agent Skill

name: hoogle description: Search Haskell APIs using Hoogle. Use this skill when working with Haskell projects to look up function signatures, find functions by type, or discover library documentation. Activate proactively when you need to understand Haskell library APIs, find the right function for a task, or look up type signatures.

Hoogle API Search

Hoogle is a Haskell API search engine. Use it to find functions by name or by type signature.

When to Use Hoogle

Use Hoogle proactively when:

Working with Haskell code and need to find a function
Looking up the type signature of a function
Searching for functions that match a type signature (e.g., a -> b -> a)
Finding which module exports a particular function
Looking up documentation for Haskell functions

Search Methods

Search by Function Name

${CLAUDE_PLUGIN_ROOT}/scripts/hoogle-search.sh "map"

Returns functions named "map" or containing "map" in their name.

Search by Type Signature

${CLAUDE_PLUGIN_ROOT}/scripts/hoogle-search.sh "a -> b -> a"

Returns functions matching that type signature. Type variables are automatically generalized.

Search with Package Filter

Include package names in the query:

${CLAUDE_PLUGIN_ROOT}/scripts/hoogle-search.sh "+base map"
${CLAUDE_PLUGIN_ROOT}/scripts/hoogle-search.sh "+containers Data.Map.lookup"

Get Detailed Info

Use --info for the first result's documentation:

${CLAUDE_PLUGIN_ROOT}/scripts/hoogle-search.sh "foldl" --info

Understanding Results

The search returns JSON with this structure:

{
  "results": [
    {
      "url": "https://hackage.haskell.org/package/base/docs/Prelude.html#v:map",
      "module": {"name": "Prelude", "url": "..."},
      "package": {"name": "base", "url": "..."},
      "item": "map :: (a -> b) -> [a] -> [b]",
      "docs": "map f xs is the list obtained by applying f to each element..."
    }
  ],
  "query": "map",
  "count": 10
}

Key fields:

item: The function signature
docs: Documentation/description
module.name: The module that exports this function
package.name: The package containing this function

Database Initialization

Before searching, ensure the Hoogle database exists:

${CLAUDE_PLUGIN_ROOT}/scripts/hoogle-init-db.sh

This checks for a valid database and generates one from Stackage if needed. Generation takes several minutes on first run.

Local Database

For project-specific searches, generate a local database:

${CLAUDE_PLUGIN_ROOT}/scripts/hoogle-init-db.sh --local /path/to/haddock/docs

Common Search Patterns

Goal	Query Example
Find function by name	`hoogle-search.sh "filter"`
Find by exact type	`hoogle-search.sh "(a -> Bool) -> [a] -> [a]"`
Find in specific package	`hoogle-search.sh "+lens view"`
Find class methods	`hoogle-search.sh "Monad m => m a -> m b"`
Find by partial type	`hoogle-search.sh "Map k v -> k -> Maybe v"`

Tips

Type signatures are powerful: Searching a -> a finds id, while [a] -> a finds head.
Use package filters: Narrow results with +packagename.
Check multiple results: The best match isn't always first.
Look at the module: Tells you what to import.

Error Handling

If searches fail with database errors, run:

${CLAUDE_PLUGIN_ROOT}/scripts/hoogle-init-db.sh --force

This regenerates the database from scratch.