LambdaHack: A game engine library for tactical squad ASCII roguelike dungeon crawlers

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LambdaHack is a Haskell game engine library for ASCII roguelike games of arbitrary theme, size and complexity, with optional tactical squad combat. It's packaged together with a sample dungeon crawler in a quirky fantasy setting. The sample game can be tried out in the browser at

Please see the changelog file for recent improvements and the issue tracker for short-term plans. Long term goals include multiplayer tactical squad combat, in-game content creation, auto-balancing and persistent content modification based on player behaviour. Contributions are welcome.

Other games known to use the LambdaHack library:

Note: All modules in this library are kept visible, to let games override and reuse them. OTOH, to reflect that some modules are implementation details relative to others, the source code adheres to the following convention. If a module has the same name as a directory, the module is the exclusive interface to the directory. No references to the modules in the directory are allowed except from the interface module. This policy is only binding when developing the library --- library users are free to access any modules, since the library authors are in no position to guess their particular needs.

This is a workaround .cabal file, flattened to eliminate internal libraries until generating haddocks for them is fixed. The original .cabal file is stored in the github repo.

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Versions 0.1.20080412, 0.1.20080413, 0.1.20090606, 0.1.20110117, 0.1.20110918, 0.2.0, 0.2.1, 0.2.6,, 0.2.8, 0.2.10,,, 0.2.12, 0.2.14,,,,,,,,,,,,,,,,,,,,,,,,
Change log
Dependencies assert-failure (>=0.1.2 && <0.2), async (>=2), base (>=4.10 && <99), base-compat (>=0.10.0), binary (>=0.8), bytestring (>=0.9.2), containers (>=, deepseq (>=1.3), directory (>=, enummapset (>=, file-embed (>=0.0.11), filepath (>=, ghc-compact, ghc-prim, ghcjs-base, ghcjs-dom (>=, hashable (>=, hsini (>=0.2), int-cast (>=0.2), keys (>=3), LambdaHack, miniutter (>=, open-browser (>=0.2), optparse-applicative (>=0.13), pretty-show (>=1.6), primitive (>=, sdl2 (>=2), sdl2-ttf (>=2), splitmix (>=0.0.3), stm (>=2.4), template-haskell (>=2.6), text (>=, th-lift-instances, time (>=1.4), transformers (>=0.4), unordered-containers (>=0.2.3), vector (>=0.11), vector-binary-instances (>=, zlib (>= [details]
License BSD-3-Clause
Author Andres Loeh, Mikolaj Konarski and others
Maintainer Mikolaj Konarski <>
Category Game Engine, Game
Home page
Bug tracker
Source repo head: git clone git://
Uploaded by MikolajKonarski at 2021-04-06T18:22:12Z


Manual Flags


switch to the vty frontend (screen reader friendly)


switch to the curses frontend (not fully supported)


switch to the GTK frontend (not fully supported)


switch to the JSaddle frontend (may be bit-rotted)


turn on expensive assertions of well-tested code


prepare for a release (expose internal functions and types, etc.)


compile so that the JS blob works in terminal with NodeJS

Automatic Flags

Use -f <flag> to enable a flag, or -f -<flag> to disable that flag. More info


Maintainer's Corner

For package maintainers and hackage trustees

Readme for LambdaHack-

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LambdaHack is a Haskell1 game engine library for ASCII roguelike2 games of arbitrary theme, size and complexity, with optional tactical squad combat. It's packaged together with a sample dungeon crawler in a quirky fantasy setting. The sample game can be tried out in the browser at

As an example of the engine's capabilities, here is a showcase of shooting down explosive projectiles. A couple were shot down close enough to enemies to harm them. Others exploded closer to our party members and took out of the air the projectiles that would otherwise harm them.

gameplay screenshot

This was a semi-automatic stealthy speedrun of the escape scenario of the sample game, native binary, SDL2 frontend, single tiny bitmap font. The enemy gang has a huge numerical and equipment superiority. Our team loots the area on auto-pilot until the first foe is spotted. Then they scout out enemy positions. Then hero 1 draws enemies and unfortunately enemy fire as well, which is when he valiantly shoots down explosives to avoid the worst damage. Then heroine 2 sneaks behind enemy lines to reach the remaining treasure. That accomplished, the captain signals retreat and leaves for the next area (the zoo).

Using the engine

To use the engine, you need to specify the content to be procedurally generated. You declare what the game world is made of (entities, their relations, physics and lore) and the engine builds the world and runs it. The library lets you compile a ready-to-play game binary, using either the supplied or a custom-made main loop. Several frontends are available (SDL2 is the default for desktop and there is a JavaScript browser frontend) and many other generic engine components are easily overridden, but the fundamental source of flexibility lies in the strict and type-safe separation of code from the content and of clients (human and AI-controlled) from the server.

Please see the changelog file for recent improvements and the issue tracker for short-term plans. Long term goals include multiplayer tactical squad combat, in-game content creation, auto-balancing and persistent content modification based on player behaviour. Contributions are welcome. Please offer feedback to or, preferably, on any of the public forums.

Other games known to use the LambdaHack library:

Note: the engine and the sample game are bundled together in a single Hackage3 package released under the permissive BSD3 license. You are welcome to create your own games by forking and modifying the single package, but please consider eventually splitting your changes into a separate content-heavy package that depends on the upstream engine library. This will help us exchange ideas and share improvements to the common codebase. Alternatively, you can already start the development in separation by cloning and rewriting Allure of the Stars10 and mix and merge with the sample LambdaHack game rules at will. Note that the LambdaHack sample game derives from the Hack/Nethack visual and narrative tradition9, while Allure of the Stars uses the more free-form Moria/Angband style (it also uses the AGPL license, and BSD3 + AGPL = AGPL, so make sure you want to liberate your code and content to such an extent).

Installation of the sample game from binary archives

The game runs rather slowly in the browser (fastest on Chrome) and you are limited to the square font for all purposes, though it's scalable. Also, savefiles are prone to corruption on the browser, e.g., when it's closed while the game is still saving progress (which takes a long time). Hence, after trying out the game, you may prefer to use a native binary for your architecture, if it exists.

Pre-compiled game binaries are available through the release page11 (and, for Windows, dev versions continuously from AppVeyor[18]). To use a pre-compiled binary archive, unpack it and run the executable in the unpacked directory or use program shortcuts from the installer, if available. On Linux, make sure you have the SDL2 libraries installed on your system (e.g., libsdl2-2.0-0 and libsdl2-ttf-2.0-0 on Ubuntu). For Windows (XP no longer supported), the SDL2 and all other needed libraries are included in the game's binary archive.

Screen and keyboard configuration

The game UI can be configured via a config file. The default settings, the same that are built into the binary, are on github at GameDefinition/config.ui.default. When the game is run for the first time, or whenever the settings file is deleted, the file is written to the default user data location, which is ~/.Allure/ on Linux, C:\Users\<username>\AppData\Roaming\LambdaHack\ (or C:\Documents And Settings\user\Application Data\LambdaHack\ or something else altogether) on Windows and Inspect/Application/Local Storage under RMB menu when run inside the Chrome browser. If the user config file is outdated or corrupted, it's automatically moved away together with old savefiles, which guarantees that the new default config file is ultimately put in its place.

Screen fonts and, consequently, window size can be changed by editing the config file in the user data folder. The default bitmap font 16x16xw.bdf used for the game map covers most national characters in the Latin alphabet (e.g. to give custom names to player characters) and results in a game window of exactly 720p HD dimensions. The 8x8xb.fnt bitmap font results in a tiny window and covers latin-1 characters only. The config file parameter allFontsScale permits further window size adjustments, automatically switching to the scalable 16x16xw.woff version of the game map font. Config file option chosenFontset governs not only the main game map font, but also the shape of the rectangular fonts, if any, in which longer texts are overlaid over the map.

For high resolution displays and/or if fullscreen mode is requested in the configuration file, allFontsScale needs to be set. E.g., scale 3 works for 4K displays. Otherwise, the letters may be too small or, in fullscreen or on retina displays in OS X, the screen may be automatically scaled as a whole, not each letter separately, softening letter edges of the square fonts that should be pixel-perfect and crisp.

If you don't have a numeric keypad, you can use the left-hand movement key setup (axwdqezc) or Vi editor keys (aka roguelike keys) or mouse. If numeric keypad doesn't work, toggling the Num Lock key sometimes helps. If running with the Shift key and keypad keys doesn't work, try the Control key instead. The game is fully playable with mouse only, as well as with keyboard only, but the most efficient combination may be mouse for menus, go-to, inspecting the map, aiming at distant positions and keyboard for everything else.

If you are using a terminal frontend, e.g. the best supported vty frontend, then numeric keypad (especially keypad * and /) may not work correctly, depending on versions of libraries, terminfo and terminal emulators. Toggling the Num Lock key may help or make issues worse. As a workaround, in the vty frontend, numbers are used for movement, which sadly prevents the number keys from selecting heroes. The commands that require pressing Control and Shift together won't work either, but fortunately they are not crucial to gameplay.

Some effort went into making the vty frontend usable with screen readers, but without feedback it's hard to say how accessible that setup is. As a side effect of screen reader support, there is no aiming line nor path in vty frontend and some of map position highlighting is performed using the terminal cursor. Screen readers may also work better with animations turned off, using --noAnim or the corresponding config file option.

Compilation of the library and sample game from source

The recommended frontend is based on SDL2, so you need the SDL2 libraries for your OS. On Linux, remember to install the -dev versions as well, e.g., libsdl2-dev and libsdl2-ttf-dev on Ubuntu Linux 16.04. Other frontends are compiled similarly, but compilation to JavaScript for the browser is more complicated and requires the ghcjs15 compiler and optionally the Google Closure Compiler16.

The latest official version of the LambdaHack library can be downloaded, compiled for SDL2 and installed automatically using the Cabal tool, which is already a part of your OS distribution, or available within The Haskell Platform7. Get the library from Hackage3 as follows

cabal update
cabal run LambdaHack

For a newer snapshot, clone the source code from github5 and run cabal run LambdaHack from the main directory. Alternatively, if you'd like to develop in this codebase, the following speeds up the turn-around a lot

cp cabal.project.local.development cabal.project.local
cabal install cabal-plan

and then compile with

cabal build .

and run the game with

make play

There is a built-in black and white line terminal frontend, suitable for teletype terminals or a keyboard and a printer (but it's going to use a lot of paper, unless you disable animations with --noAnim). It is used in CI and for some tests and benchmarks defined in Makefile. To compile with one of the less rudimentary terminal frontends (in which case you are on your own regarding font choice and color setup and you won't have the spiffy colorful squares outlining special positions that exist in SDL2 frontend, but only crude cursor highlights), use Cabal flags, e.g, to switch to the vty console frontend optimized for screen readers, run

cabal run -fvty LambdaHack

Testing and debugging

The Makefile contains many sample test commands. Numerous tests that use the screensaver game modes (AI vs. AI) and the teletype frontend are gathered in make test. Of these, travis runs test-travis on each push to github. Test commands with prefix frontend start AI vs. AI games with the standard, user-friendly frontend and auto-locating the game binary.

Run LambdaHack --help to see a brief description of all debug options. Of these, the --sniff option is very useful (though verbose and initially cryptic), for displaying the traffic between clients and the server. Some options in the config file may prove useful too, though they mostly overlap with commandline options (and will be totally merged at some point).

You can use HPC with the game as follows (details vary according to HPC version).

cabal clean
cabal build --enable-coverage
make test
hpc report --hpcdir=dist/hpc/dyn/mix/LambdaHack --hpcdir=dist/hpc/dyn/mix/LambdaHack-xxx/ LambdaHack
hpc markup --hpcdir=dist/hpc/dyn/mix/LambdaHack --hpcdir=dist/hpc/dyn/mix/LambdaHack-xxx/ LambdaHack

A quick manual playing session, after the automated tests, would be in order as well, since the tests don't touch the topmost UI layer. Note that a debug option of the form --stopAfter* is required to cleanly terminate any automated test. This is needed to gather any HPC info, because HPC requires a clean exit to save data files.

Coding style

Stylish Haskell is used for slight auto-formatting at buffer save; see .stylish-haskell.yaml. As defined in the file, indentation is 2 spaces wide and screen is 80-columns wide. Spaces are used, not tabs. Spurious whitespace avoided. Spaces around arithmetic operators encouraged. Generally, relax and try to stick to the style apparent in a file you are editing. Put big formatting changes in separate commits.

Haddocks are provided for all module headers and for all functions and types from major modules, in particular for the modules that are interfaces for a whole directory of modules. Apart of that, only very important functions and types are distinguished by having a haddock. If minor ones have comments, they should not be haddocks and they are permitted to describe implementation details and be out of date. Prefer assertions instead of comments, unless too verbose.

The 'pointman' from game manual and UI is called 'leader' in the source code and there are a few more mismatches, though the source code naming and the UI naming should each be consistent in separation. If the UI names stick, perhaps source code will be renamed at some point.

This codebase is an experiment in extensive use of states without lens. So far, it works, doesn't result in much larger files or lots of repetition and has the added benefits that newcomers don't need to learn any lens library. Record punning, etc., definitely helps.

Further information

For more information, visit the wiki4 and see, CREDITS and COPYLEFT.

Have fun!