Interpreter for SiFun (Simple Functional) Language with three different type systems (supports Higher-Rank Polymorphism).

Currently supports Hindley–Milner type system (simply typed lambda calculus) and Hindley–Milner with Visible Type Application (similar to System F).

Under development is a Bidirectional Typechecking System which will support Higher-Rank Polymorphism without typed function and type application.

Installation

You can clone this repository using:

git clone git@github.com:kkd26/SiFun.git
cd SiFun
opam install .

or use the official opam release using:

opam install sifun

Usage

There are two ways to interact with the interpreter:

1. SiFun REPL (Read–eval–print loop) - interactive console

   sifuni
   

2. SiFun Interpreter - run from file

   sifun <filename>
   

SiFun Language syntax

The basic language supports (similar to Hindley–Milner type system):

• integers 1, 2, 3, ...

• booleans true, false

• variables x, y, ...

• pairs (1, true)

• first and second fst (1,3), snd (4,5), ...

• functions fn x => x, fn x => fn y => (x,y), ...

• application (fn x => (1,x)) 2, ...

The additional features are (similar to System F):

• typed functions fn x : int => x, ...

• type variables a, b, c, ...

• poly types forall a. a->a, forall a b c. a->b->c, ...

• big lambda lam a. (int, fn x : a => x), lam a b c. fn x : a => x, ...

• type application (lam a. fn x : a => x) {int}, ...

Note that ; separates blocks of code and ;; sends EOF, so stops execution.

You can check ./examples for more information about the syntax and semantics.