Ansiform targets Linux, macOS and Windows. The pure builders, layout and rendering code are portable. The differences are in terminal detection, key delivery and terminal size.

• ansi-terminal writes ANSI sequences and provides the same operations through the Windows console API when native support is missing.
• terminal-size queries the size through ioctl on POSIX and the Win32 console API on Windows.
• base supplies handles, echo control, buffering and hWaitForInput.
• Nothing depends on unix. On Windows the dependency graph includes Win32 only through terminal-size.

Everything in this documentation applies as written. hIsTerminalDevice recognises the terminal, hSetBuffering and hSetEcho change the terminal mode, and escape sequences arrive as ordinary input. Terminal.app and iTerm2 send the CSI sequences listed in Input.

Configured colour detection uses hSupportsANSI, which checks that the output handle is a terminal and that TERM is not dumb. NO_COLOR still disables styling.

Escape-sequence timeouts use hWaitForInput, so a lone Escape or an arrow key never interrupts a blocked read with an asynchronous exception. Without -threaded, hWaitForInput blocks other Haskell threads for the length of the timeout; this is fine for the single-threaded interaction loop and avoids a thread per keystroke.

ANSI output, cursor movement and width queries work through ansi-terminal and terminal-size in cmd.exe, Windows Terminal and applications built with a native console. On Windows 10 and later the console processes ANSI sequences; on older consoles ansi-terminal emulates the operations it supports.

The size query runs only when the handle is a terminal. This avoids the stty fallback in terminal-size, which on Windows can close a non-console handle. As a consequence, MinTTY and MSYS sessions, whose handles look like pipes, use the 80 by 24 default instead of a detected size.

Immediate input needs console input that does not wait for Enter. In GHC 9.14.1 the Windows build of the runtime enables the winio I/O manager but keeps mio as the default for the threaded runtime and win32-legacy as the default for the non-threaded runtime. With those defaults, hSetBuffering stdin NoBuffering may not take effect and getChar can wait for Enter, which is the long-standing behaviour tracked as GHC issue 2189.

Select the native manager when building an interactive program:

if os(windows)
  ghc-options: -with-rtsopts=--io-manager=winio

The bundled ansiform-demo and ansiform-tutorial executables already set this option on Windows. Libraries cannot set RTS options, so applications that embed Ansiform must add it themselves.

hIsTerminalDevice stdin is reliable for the native console and Windows Terminal. MinTTY, MSYS and Cygwin connect standard input through pipes, so Ansiform sees a non-interactive stdin: immediate input is not enabled, readKeyPress returns characters only when a line is available, and forms fall back to line reading. Use Windows Terminal or cmd.exe for interactive screens.

The library handles the common Windows key codes: Enter arrives as \r or \n, and Backspace as \b or DEL. Arrow keys reach readKeyPress and the line editor only when the console delivers them as escape sequences. If the console instead reports them as key events, getChar cannot return them and the application sees no input for those keys; this requires Win32 input APIs, which Ansiform does not use. readKeyPress still protects every shortcut from any sequence that is delivered.

GHC uses the console code page for console input and output. Run chcp 65001 and use a font with the required glyphs to display wide characters. The layout code measures them correctly even when the console cannot render them.

• Immediate input through MinTTY, MSYS or Cygwin pipes.
• Mouse input.
• Bracketed paste.
• Grapheme-cluster cursor movement. Editing and cursor movement work by Unicode code point, so combining marks may be split.

The CI matrix builds, tests, checks, documents and packages the library on Linux, macOS and Windows. Linux and Windows use GHC 9.2.8 and GHC 9.14.1. macOS uses macos-15-intel with GHC 9.2.8 and macos-15 with GHC 9.14.1: the arm64 runner has no GHC 9.2.8 bindist, and the SDK on macos-latest is too new for the GHC 9.14.1 linker. A quality job checks formatting and linting, and a separate workflow scans for secrets. CI still cannot press keys, so the interaction statements above come from the GHC, ansi-terminal, terminal-size and base documentation and the manual checklist below.

A manual checklist for each platform:

1. Draw a page, press a key and confirm that the screen changes without Enter.
2. Press the four arrows in a menu and confirm that no shortcut runs.
3. Open a form with promptWithInitial, move, insert, Backspace, Delete, Home, End, submit with Enter and cancel with Esc.
4. Type a value wider than the terminal and confirm that the window scrolls with the cursor.
5. Confirm that colours appear on a terminal and disappear when output is redirected.
6. Resize the terminal and confirm that the layout uses the new width.

On 2026-10-21 the checklist was executed on Linux under a pseudo-terminal. The first run found the lone-Escape timeout fixed in 0.9.0.6. A second run for 1.0.0 confirmed all six items and that every prefilled field is visible as soon as the edit form opens. macOS and Windows still need the same run on real terminals.