LCI is an interpreter for the lambda calculus. It supports many advanced features such as recursion, user-defined operators and multiple evaluation strategies, all based on the pure calculus. It is free software licenced under the GNU General Public Licence (GPL).
Try it online
LCI can be considered a small (but powerfull) functional progamming language based on the pure lambda-calculus. Its features include:
- Aliases of lambda terms (that is named functions).
- Integers coded as church numerals, with the usual arithmetic operations.
- Recursion. Self-references of aliases are expanded during execution. LCI can also automatically convert recursive terms to non-recursive ones using a fixed point combinator.
- User-defined operators. The user can declare a new
operator with a certain precedence and associativity and define it in lambda
calculus. Many common operators (eg. integer, logic and list operations) are
.lcircand are available by default.
- List syntax.
[a,b,c]is parsed as
Nilare defined in
- Multiple evaluation strategies. Call-by-name and call-by-value can coexist in the same program.
- Human-readable display of terms: for example church numerals are
displayed as numbers and lists using the
- Tracing of execution.
- File interpretation as well as interactive usage.
- A library of pre-defined functions (
All features are implemented in the pure lambda calculus.
To demonstrate them, there is an implementation of the N-Queens problem
queens.lci) in a way that reminds of Haskell syntax.
The latest version is available here. To install extract the archive, cd to that directory and run:
cmake -B build
cd build && make
sudo make install
This will install the
lci executable in
.lcirc, queens.lci in
/usr/local/share/lci. You can install then in a different location by passing
You can also checkout the code from github.
Using Homebrew on OSX
Install Homebrew and run:
brew install lci
Binaries for Windows
Windows binaries are
Simply extract and run the
Building for WebAssembly
The browser version can be built with emscripten.
You first need to build
make_dparser with a normal build, then build
emcmake. The build is created under
mkdir build && cd build
emcmake cmake ..
If you have found a bug please report it. Also feel free to send pull requests, or suggest features.
LCI’s documentation covers most of the program’s features and explains various topics concerning the lambda-calculus