The initial purpose of this project was just to try setting up a real-world Haskell project with stack, cleanly written and tested.
It ended up in an interesting task of understanding and implementing a normalizer for the untyped lambda calculus.
There is a command-line interface to the normalizer, which can most easily be accessed via stack exec mini-lambda. Currently, this does only run the full reduction and prints the result. The syntax is defined as follows:
EXPR = VAR
| "(" LAMBDA VAR "." EXPR ")"
| "(" EXPR EXPR ")"
LAMBDA = "λ" | "\\" (a single backspace)
VAR = (['!'..'\''] | ['*'..'-'] | ['/'..'['] | [']'..'~'])+
This means that every lambda and every application have to be fully parenthesized -- this might get improved in the future. For more details, see Parser.hs (the parser combinator used is self-written, just for fun, so there's poor error handling).