vty

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`vty` is a terminal interface library. It provides a high-level
interface for doing terminal I/O. Vty is supported on GHC versions
7.10.1 and up.

`vty` and its partner packages are published on
[Hackage](https://hackage.haskell.org/). The `vty` package works in
concert with one or more *platform packages* to do terminal I/O. Each
platform package provides support for terminal I/O on a specific
platform. Known platform packages are:

* [vty-unix](https://github.com/jtdaugherty/vty-unix) - the Unix
  terminal backend for Vty
* [vty-windows](https://github.com/chhackett/vty-windows) - the Windows
  terminal backend for Vty
* [vty-crossplatform](https://github.com/jtdaugherty/vty-crossplatform) -
  a package that builds `vty-unix` or `vty-windows` based on the build
  environment

# How to use Vty

1. Add a package dependency on `vty-unix`, `vty-windows,` or
   `vty-crossplatform`, depending on the desired level of platform
   support. For example, if an application only supports Unix systems,
   it should depend on `vty-unix`. But if an application is intended to
   work anywhere Vty works, then `vty-crossplatform` is the best choice.
2. Add a package dependency on `vty`; the core library abstractions,
   types, and functions are obtained from `vty` itself. The platform
   packages do not re-export the core library's modules.
3. Import `mkVty` from the platform package in step (1) and use that to
   construct a `Vty` handle and initialize the terminal.
4. If desired, call `Graphics.Vty.Config.userConfig` to load the Vty
   user configuration since this step is not automatic.

Once you've initialized the terminal and have a `Vty` value, all of the
`vty` package's API is now ready to use to do terminal I/O.

# Implementing support for a new platform

Although this shouldn't be necessary to do very often (if ever!), if
you would like to implement support for a new platform for Vty, see
`PLATFORM-HOWTO.md`.

# Features

* Provides an efficient output algorithm. Output buffering and terminal
  state changes are minimized.

* Automatically handles window resizes.

* Minimizes repaint area, which virtually eliminates the flicker
  problems that plague ncurses programs.

* Provides a pure, compositional interface for efficiently constructing
  display images.

* Automatically supports refresh on Ctrl-L.

* Provides extensible input and output interfaces.

* Properly handles cleanup (but not due to signals).

* Provides a comprehensive test suite.

* Supports "normal" and "extended" (SGR) mouse modes as described at
  http://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h2-Mouse-Tracking

* Supports bracketed paste mode as described at
  http://cirw.in/blog/bracketed-paste

* Supports multi-column Unicode characters such as emoji characters. In
  cases where Vty and your terminal emulator disagree on character
  widths, Vty provides a tool `vty-build-width