hoogle

# Hoogle [![Hackage version](https://img.shields.io/hackage/v/hoogle.svg?label=Hackage)](https://hackage.haskell.org/package/hoogle) [![Stackage version](https://www.stackage.org/package/hoogle/badge/nightly?label=Stackage)](https://www.stackage.org/package/hoogle) [![Build status](https://img.shields.io/github/actions/workflow/status/ndmitchell/hoogle/ci.yml?branch=master)](https://github.com/ndmitchell/hoogle/actions)

Hoogle is a Haskell API search engine, which allows you to search many standard Haskell libraries by either function name, or by approximate type signature. The online version can be found at https://hoogle.haskell.org/ and searches [Stackage](https://www.stackage.org/).

* **Online version:** https://hoogle.haskell.org/
* **Hackage page:** https://hackage.haskell.org/package/hoogle
* **Source code:** https://github.com/ndmitchell/hoogle
* **Bug tracker:** https://github.com/ndmitchell/hoogle/issues

## Hoogle Use

Hoogle can be used in several ways:

* **Online**, with the web interface at https://hoogle.haskell.org/
* **In [IRC](https://wiki.haskell.org/IRC_channel)**, using the [Lambdabot](https://wiki.haskell.org/Lambdabot) plugin with `@hoogle` and `@hoogle+`
* **From `emacs`**, by means of [`engine-mode`](https://github.com/hrs/engine-mode)
* **[Installed locally](./docs/Install.md)**, with either a command line or in a browser
* **[As a developer](./docs/API.md)**, through Haskell or JSON APIs.

# Searches

## Searching

Here are some example searches:

* `map` searches as text, finding `map`, `concatMap`, `mapM`
* `con map` searches for the text "map" and "con" finding `concatMap`, but not `map`
* `a -> a` searches by type, finding `id :: a -> a`
* `a` searches for the text "a"
* `:: a` searches for the type "a"
* `id :: a -> a` searches for the text "id" and the type "a -> a"


## Scope

By default, searches look at the [Haskell Platform](https://www.haskell.org/platform/) and [Haskell keywords](https://wiki.haskell.org/Keywords). However, all [Stackage](https://stackage.org) packages are available to search. As some examples:

* `mode +cmdargs` searches only the "cmdargs" package
* `file -base` searches the Haskell Platform, excluding the "base" package
* `mode +platform +cmdargs` searches both the Haskell Platform and the "cmdargs" package
* `count +missingh` searches only the "MissingH" package - all packages are written in lower-case

With the set of packages you are searching, you can also restrict the set of modules searched:

* `file -System` excludes results from modules such as `System.IO`, `System.FilePath.Windows` and `Distribution.System`
* `fold +Data.Map` finds results in the `Data.Map` module


# Integration

## Command Line Version

To invoke Hoogle type:

    $ hoogle "[a] -> [b]"

Note the quotes, otherwise you will redirect the output to the file [b].

To ensure you have data files for the Hackage modules, you will first need to
type:

    $ hoogle generate

Which will download and build Hoogle databas