landler

An extended λ-calculus interpreter

A λ-calculus interpreter

At its core, landler is a λ-calculus evaluation library and a command-line program that wraps around it. For instance, you can use the library interactively with GHCi:

% ghci
GHCi, version 7.0.4: http://www.haskell.org/ghc/  :? for help
Prelude> :m +Language.Landler
Prelude Language.Landler> dance "(\\x y. y x) World Hello"
[(((\x y. y x) World) Hello,"subst"),((\y. y World) Hello,"subst"),(Hello World,"stuck")]

The command-line program, landler provides a convenient interface to the library and includes some extra features such as let-bindings:

% cat > fix.lambda
let id = (\x. x)
let fix = (\f. (\x. f (x x)) (\x. f (x x)))
(fix id)

% landler fix.lambda
fix id
    name-rep
(\f. (\x. f (x x)) (\x. f (x x))) id
    subst
(\x. id (x x)) (\x. id (x x))
    subst
id ((\x. id (x x)) (\x. id (x x)))
    name-rep
(\x. x) ((\x. id (x x)) (\x. id (x x)))
    subst
(\x. id (x x)) (\x. id (x x))
    cycling
---

The landler CLI program can also be used as a REPL; just run it without any arguments:

% landler
landler, version <VERSION>: https://github.com/scvalex/landler  :? for help
∅ > ((\x. x) y)
[((\x. x) y,"subst"),(y,"stuck: top-level is not an application")]
∅ > type (\x y. x)
b → c → b

Development

Development is Makefile-driven™. That is, I run everything through the Makefile.

To build landler, run:

% make

To build the documentation, run:

% make doc

To install:

% make install

To run the tests (both unit and quickcheck):

% make test

Note that most of these just invoke cabal behind the scenes.