1. git clone https://github.com/ulan/hindley-milner-exercise.git
2. cd hindley-milner-exercise
3. cabal test
4. cabal build
5. ./dist/build/hindley-milner-exercise/hindley-milner-exercise < your-program-source.txt

A term of the language is one of:

• A variable - any sequence of letters (except one of the keywords).
• A lambda application - two terms separated by a white space.
• A lambda abstraction - written as "\variable . term"
• A (non-recursive) let expression - written as "let variable = (term1) in term2", where the variable doesn't occur in term1 and paranthesis around term1 cannot be omitted.
• A fix expression - written as "fix variable . term", where the variable may occur in the term. Its semantic is given by "fix x . M --> M[x := fix x . M]" (monomorphic type inference for 'fix' is enough)
• A parenthesized expression - written as "(term)". Allows expressions like (x z) (y z).
• Integer (decimal) constant.
• Boolean constant: true | false.

Builtins:

• cmp : Number -> Number -> Bool - comparison.
• add : Number -> Number -> Number - addition.
• sub : Number -> Number -> Number - subtraction.
• mul : Number -> Number -> Number - multiplication.
• div : Number -> Number -> Number - division.
• if : forall a . Bool -> a -> a -> a - conditional.