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https://github.com/ejgallego/HOARe2

Higher-Order Approximate Relational Refinement Types for Mechanism Design and Differential Privacy
https://github.com/ejgallego/HOARe2

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Higher-Order Approximate Relational Refinement Types for Mechanism Design and Differential Privacy

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README 

        
# Welcome to the HOARe² compiler distribution!



[![Build Status](https://travis-ci.com/ejgallego/HOARe2.svg?branch=master)](https://travis-ci.com/ejgallego/HOARe2)



We provide the type checker and examples used in papers:



* "Higher-Order Approximate Relational Refinement Types for Mechanism

   Design and Differential Privacy"

   - ACM: http://dl.acm.org/citation.cfm?id=2677000

   - ArXiV: http://arxiv.org/abs/1407.6845



* "Computer-aided verification in mechanism design"

   - ACM: https://dl.acm.org/citation.cfm?id=3081132

   - ArXiV: http://arxiv.org/abs/1502.04052



## Build instructions:



We recommend using OPAM 2.0 to install the tool, you'll need a recent

repository and standard gnu tools (gcc and make). Note the concrete

versions needed, in particular you need why3 1.2.1. In case of doubt,

the `.travis.yml` file should contain reproducible build

instructions. A typical workflow is:



```

$ opam install --deps-only -d -t .

$ why3 config --detect

$ dune build

$ dune exec -- arlc -L examples/popl/ examples/popl/dummysum.rlc

```



### Provers:



You want to install some SMT solvers to run the tool.

We recommend the following set:



```

$ why3 config --detect

Found prover Alt-Ergo version 2.3.0, OK.

Found prover CVC4 version 1.6, OK.

Found prover CVC4 version 1.4

Found prover CVC3 version 2.4.1, OK.

Found prover Eprover version 2.3, OK.

```



You may be lucky with other versions. Links:



- Alt-Ergo: (http://alt-ergo.ocamlpro.com/)

- CVC3 2.4.1 and CVC4 1.4 / 1.6:

  http://www.cs.nyu.edu/acsys/cvc3/

  http://cvc4.cs.nyu.edu/web/

- Eprover 2.0:

  http://wwwlehre.dhbw-stuttgart.de/~sschulz/E/E.html



### Running HOARe²:



To type-check a program just run:



```

$ dune exec -- arlc examples/ex01

```



`arlc --help` should display help for the tool.



## Editing and viewing examples:



The examples are in the examples/ directory.



We recommend using Emacs and Tuareg-mode to open the .rlc files. It is

not perfect but it does a good job, as our syntax is closely based on

OCaml's one.



You can add:



```

(add-to-list 'auto-mode-alist '("\\.rlc$"      . tuareg-mode) t)

```



to your emacs to automate the mode-loading process.



### Reproducing results:



The provided Travis setup does provide a reproducible checking of the

main examples, including `summarization`. Our CI setup will fail for

any commit that breaks this.



Note that the `binary` example produces .why files to be verified

using the Why3 IDE. We hope to improve this. Use



```

$ why3 ide -I examples/popl $file

```

to proceed.



In particular:



- `examples/binary_vc_length_power_0.why`:



  Requires the use of Eprover, it will then check.



- `examples/binary_vc_m_ass_0_solved.why`:



  This one is tricky and needs Eprover and CVC3 to check.



## More about the tool



If you are curious about the examples individually, we provide several

verbosity options to witness the type checking process `-v 1` to `-v 9`.



Depending on your machine the solvers may need a larger timeout. You

can control it using the --timeout parameter but the default should be

fine for most.



Some examples may take a long time, if they fail with a timeout,

try increasing it:



```

$ dune exec -- arlc --timeout 90 examples/summarization.rlc

```



The tool is in alpha stage, it may be difficult to use for your own

particular programs, but we would be happy to help.



The most common failure of the typechecking is solvers failing to

verify an assertion. If that happens, you can use:



```

$ why3 ide arlc_current.why

```



to play with the proof context and debug the cause of failure.



## Limitations of the tool



There are two important limitations of the tool, however  workarounds do exists:



- Bidirectional type-checking is very limited at the moment. This

  means that you may need to use a cut (see eq_v in dummysum.rlc for

  example) in the leaves to hint the type checker about the return

  type.



  Also `match` expressions do require annotations.



- Assertion checking may fail with an error if the assertion cannot be

  translated to Why3. Why3 has limited support for higher-order and we

  have not implemented a complete defunctionalization/demonadlization

  procedure yet.



  In most cases is possible to factorize the program to avoid

  this error.



## Language extensions



In order to help with development, two helper primitives "trust" and

"have" are supported.



```

have : { Assertion }        in

```



Will introduce a cut or intermediate lemma for helping the SMT. In

quite a few cases, the SMTs cannot prove A -> B directly, but with a

hint C, they are able to prove A -> C, and C -> B. (We usually

discover this conditions using why3ide).



The `have` primitive just eases the introduction of cuts.



```

trust (ass_name) res : T = e in

```



Will consider e to have type T without calling the SMTs. However, it

will output the pending proof to a file "ass_name.why", allowing to

prove it using the why3ide. We also output a Coq file for the

Coq-inclined user.



We hope you have fun, don't hesitate to contact us for any question or

help.



## Language reference:



TODO