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

1. Type signatures are powerful: Searching a -> a finds id, while [a] -> a finds head.
2. Use package filters: Narrow results with +packagename.
3. Check multiple results: The best match isn't always first.
4. 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.