pi-forall
=========
   A demo implementation of a simple dependently-typed language for OPLSS 2013
	Stephanie Weirich

The goal of this project is to bring up the design issues that occur in the
implementation languages like Agda, Coq, Epigram, Idris, etc. Of course, it
can't cover everything, but this code is a good starting point for discussion.

As it's main purpose is didactic, the code itself has been written for
clarity, not for speed. The point of this implementation is an introduction to
practical issues of language design and how specific features interact with
each other. 

Furthermore, this code based includes a number of features (unit, booleans,
sigma types) which are all subsumed by the general mechanism for
datatypes. These are included to give examples before diving into the more
general, and much more complicated, code. 


Features
--------
  - PTS representation (uniform syntax for all levels)
  - bidirectional type checking
  - erased arguments (forall)
  - propositional equality 
  - inductive & indexed datatypes 

Not covered (Future work!)
--------------------------
  - nontermination
  - effects
  - co-induction
  - type inference & unification
  - general constraint solving

This code is open source. Feel free to extend or adapt it for your own
project. The definitive version will be uploaded to github after the summer 
school is complete. 
  https://github.com/sweirich/pi-forall

Caveat 
------
There will be bugs. There will be *design* bugs. The language is probably not
sound. Or may not be so in the presence of 'innocent' axioms like classical
logic. Even in this little language there are many semantic pitfalls. C'est la
vie.

Installation
----------
  pi-forall requires GHC and cabal, most easily available from 
  the Haskell Platform (http://www.haskell.org/platform/) 
  
  in the top level directory type 'cabal install'

Contents
--------
pi-forall/
  README (this file)
  LICENSE
  pi-forall.cabal
  test/*.pi          example files
  src/*.hs           source code

Acknowledgement
---------------

Some of this code was adapted from the 'zombie-trellys' implementation by the
Trellys team. The Trellys team includes Aaron Stump, Tim Sheard, Stephanie
Weirich, Garrin Kimmell, Harley D. Eades III, Peng Fu, Chris Casinghino,
Vilhelm Sjöberg, Nathan Collins, and Ki Yung Ahn.

This material is based upon work supported by the National Science Foundation
under Grant Number 0910786. Any opinions, findings, and conclusions or
recommendations expressed in this material are those of the author(s) and do
not necessarily reflect the views of the National Science Foundation.