vty: A simple terminal UI library

[ bsd3, library, program, user-interfaces ] [ Propose Tags ]

vty is terminal GUI library in the niche of ncurses. It is intended to be easy to use, have no confusing corner cases, and good support for common terminal types.

See the vty-examples package as well as the program test/interactive_terminal_test.hs included in the vty package for examples on how to use the library.

Import the Graphics.Vty convenience module to get access to the core parts of the library.

© 2006-2007 Stefan O'Rear; BSD3 license.

© Corey O'Connor; BSD3 license.

© Jonathan Daugherty; BSD3 license.

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Versions [RSS] 3.0.0, 3.0.1, 3.0.2, 3.0.4, 3.1.0, 3.1.2, 3.1.4, 3.1.6, 3.1.8,,, 4.0.0,,,,,,,,,,,,,,,,,, 4.7.1, 4.7.2, 4.7.3, 4.7.4, 4.7.5, 5.0.0, 5.0.1, 5.0.2, 5.1.0, 5.1.1, 5.1.3, 5.1.4, 5.2.0, 5.2.1, 5.2.2, 5.2.3, 5.2.4, 5.2.5, 5.2.6, 5.2.7, 5.2.8, 5.2.9, 5.2.10, 5.2.11, 5.3, 5.3.1, 5.4.0, 5.5.0, 5.6, 5.7, 5.7.1, 5.8, 5.8.1, 5.9, 5.9.1, 5.10, 5.11, 5.11.1, 5.11.2, 5.11.3, 5.12, 5.13, 5.14, 5.15, 5.15.1, 5.16, 5.17, 5.17.1, 5.18, 5.18.1, 5.19, 5.19.1, 5.19.2, 5.20, 5.21, 5.22, 5.23, 5.23.1, 5.24, 5.24.1, 5.25, 5.25.1, 5.26, 5.27, 5.28, 5.28.1, 5.28.2, 5.29, 5.30, 5.31, 5.32, 5.33, 5.34, 5.35, 5.35.1, 5.36, 5.37 (info)
Change log CHANGELOG.md
Dependencies base (>=4.8 && <5), blaze-builder (>= && <0.5), bytestring, containers, deepseq (>=1.1 && <1.5), directory, filepath (>=1.0 && <2.0), hashable (>=1.2), microlens (<0.4.10), microlens-mtl, microlens-th, mtl (>= && <2.3), parallel (>=2.2 && <3.3), parsec (>=2 && <4), semigroups (>=0.16), stm, terminfo (>=0.3 && <0.5), text (>=0.11.3), transformers (>=, unix, utf8-string (>=0.3 && <1.1), vector (>=0.7), vty [details]
License BSD-3-Clause
Maintainer Jonathan Daugherty (cygnus@foobox.com)
Revised Revision 1 made by HerbertValerioRiedel at 2019-01-22T10:32:19Z
Category User Interfaces
Home page https://github.com/jtdaugherty/vty
Source repo head: git clone https://github.com/jtdaugherty/vty.git
Uploaded by JonathanDaugherty at 2018-03-17T16:42:58Z
Distributions Arch:5.37, Debian:5.28.2, Fedora:5.33, LTSHaskell:5.37, NixOS:5.33, Stackage:5.37, openSUSE:5.33
Executables vty-demo, vty-mode-demo
Downloads 105237 total (330 in the last 30 days)
Rating 2.5 (votes: 3) [estimated by Bayesian average]
Your Rating
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Status Docs available [build log]
Last success reported on 2018-03-17 [all 1 reports]

Readme for vty-5.21

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Build Status

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.

Install via git with:

git clone git://github.com/jtdaugherty/vty.git

Install via cabal with:

cabal install vty


  • Supports a large number of terminals. vt100, ansi, hurd, linux, screen, etc., or anything with a sufficient terminfo entry.

  • Automatic handling of window resizes.

  • Unicode output on terminals with UTF-8 support.

  • Handles multi-column glyphs. (Requires user to properly configure terminal.)

  • Efficient output. Output buffering and terminal state changes are minimized.

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

  • A pure, compositional interface for efficiently constructing display images.

  • Automatically decodes keyboard keys into (key,[modifier]) tuples.

  • Automatically supports refresh on Ctrl-L.

  • Supports a keypress timeout after for lone ESC. The timeout is customizable.

  • The interface is designed for easy extension.

  • Supports ANSI graphics modes (SGR as defined in console_codes(4)) with a type-safe interface and graceful fallback for terminals with limited or nonexistent support for such modes.

  • 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

Development Notes

Vty uses threads internally, so programs made with Vty need to be compiled with the threaded runtime using the GHC -threaded option.

Platform Support

Posix Terminals

Uses terminfo to determine terminal protocol. With some special rules to handle some omissions from terminfo.


Unsupported (but contributions and testing here are very welcome!)


If you decide to contribute, that's great! Here are some guidelines you should consider to make submitting patches easier for all concerned:

  • If you want to take on big things, talk to me first; let's have a design/vision discussion before you start coding. Create a GitHub issue and we can use that as the place to hash things out.
  • If you make changes, make them consistent with the syntactic conventions already used in the codebase.
  • Please provide Haddock documentation for any changes you make.

Development Notes

Under NixOS

Using cabal

After installing ncurses to the user environment:

LIBRARY_PATH=$HOME/.nix-profile/lib/ cabal configure --enable-tests --extra-lib-dirs=$HOME/.nix-profile/lib
LIBRARY_PATH=$HOME/.nix-profile/lib/ cabal build
LIBRARY_PATH=$HOME/.nix-profile/lib/ cabal test

Code Coverage

As of last testing, profiling causes issues with coverage when enabled. To evaluate coverage, configure as follows:

rm -rf dist ; cabal configure --enable-tests --enable-library-coverage \
  --disable-library-profiling \


rm -rf dist ; cabal configure --enable-tests --disable-library-coverage \
  --enable-library-profiling \

Known Issues

  • Terminals have numerous quirks and bugs. Vty picks what works best for the author in ambiguous or buggy situations.

  • Signal handling of STOP, TERM and INT are nonexistent.

  • The character encoding of the terminal is assumed to be UTF-8 if unicode is used.

  • Terminfo is assumed to be correct unless there is an override configured. Some terminals will not have correct special key support (shifted F10 etc). See Config for customizing vty's behavior for a particular terminal.

  • Uses the TIOCGWINSZ ioctl to find the current window size, which appears to be limited to Linux and BSD.


Good sources of documentation for terminal programming are: