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 http://lambdahack.github.io.
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. Actual in-game footage.
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
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 firstname.lastname@example.org or, preferably, on any of the public forums.
Other games known to use the LambdaHack library:
- Allure of the Stars6, a near-future Sci-Fi game
Note: the engine and the sample game are bundled together in a single
Hackage3 package released under the permissive
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). 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,
~/.Allure/ on Linux,
C:\Documents And Settings\user\Application Data\LambdaHack\
or something else altogether) on Windows
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
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
version of the game map font. Config file option
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
/) 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 or main game menu options.
Compilation of the library and sample game from source
The latest official version of the LambdaHack library can be downloaded, compiled for SDL2 and installed automatically using the 'cabal' tool, which may already be a part of your OS distribution, but if it's too old (version 3.4 or later is required) you can download the whole current compilation suite as described at https://www.haskell.org/downloads/. Get the LambdaHack package from Hackage3 as follows
cabal update cabal run LambdaHack
For a newer snapshot, clone the source code from github5
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
and then you can compile (and recompile) with
cabal build .
and run the game with
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
Unit tests and integration tests can be run and displayed with
cabal test test --enable-tests --test-show-details=direct
To prepare doctests7, set
tests: True in your
Afterwards, doctests can be executed with
cabal build . && cabal exec cabal test doctests
and their detailed results observed in a log file.
cabal build before each testsuite run is requied
due to bug https://github.com/haskell/cabal/issues/7522.)
contains many sample automated play test commands.
Numerous tests that use the screensaver game modes (AI vs. AI)
and the teletype frontend are gathered in
Some of these are run by CI 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.
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).
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.
CI checks the code with
hlint . using the very liberal configuration
.hlint.yaml. If hlint is still too naggy, feel free to add
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.