Primary repository for Haskell VTY library
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Build Status

vty is a terminal interface library.

This project is hosted on

Install via git with:

git clone git://

Install via cabal with:

cabal install vty


  • Support for a large number of terminals. vt100, ansi, hurd, linux, screen etc etc. Anything with a sufficient terminfo entry.

  • Automatic handling of window resizes.

  • If the terminal support UTF-8 then vty supports Unicode output.

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

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

  • Minimizes repaint area. Virtually eliminating the flicker problems that plagues 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.

  • Automatically supports timeout after for lone ESC. The timeout is customizable.

  • Interface is designed for easy compatible extension.

  • Supports ANSI graphics modes (SGR as defined in console_codes(4)) with a type-safe interface. Gracefull fallback for terminals that do not support, or partially support the standard ANSI graphics modes.

  • Properly handles cleanup, but not due to signals.

  • Comprehensive test suite.

Known Issues

  • Terminals have numerous quirks and bugs. vty picks what works best for the author in ambigious, or buggy situations.

  • Signal handling of STOP, TERM and INT are non existent.

  • 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.

  • Supports "normal" and "extended" (SGR) mouse modes as described at

  • Supports bracketed paste mode as described at

Platform Support

Posix Terminals

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


cygwin only.

Development Notes

Under NixOS

Using cabal

After installing ncurses to user env.

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

Using stack

stack build
stack test
stack install


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 \