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Liquid Fixpoint

This package implements a Horn-Clause/Logical Implication constraint solver used for various Liquid Types. The solver uses SMTLIB2 to implement an algorithm similar to:

• Houdini
• cartesian predicate abstraction

Requirements

In addition to the .cabal dependencies you require an SMTLIB2 compatible solver binary:

• Z3
• CVC4
• MathSat

If on Windows, please make sure to place the binary and any associated DLLs somewhere in your path.

How To Build and Install

Simply do:

git clone https://github.com/ucsd-progsys/liquid-fixpoint.git
cd liquid-fixpoint
stack install

or (cabal instead of stack if you prefer.)

Using SMTLIB-based SMT Solvers

You can use one of several SMTLIB2 compliant solvers, by:

fixpoint --smtsolver=z3 path/to/file.hs

Currently, we support

* Z3
* CVC4
* MathSat

Configuration Management

It is very important that the version of Liquid Fixpoint be maintained properly.

Suppose that the current version of Liquid Haskell is A.B.C.D:

• After a release to hackage is made, if any of the components B, C, or D are missing, they shall be added and set to 0. Then the D component of Liquid Fixpoint shall be incremented by 1. The version of Liquid Fixpoint is now A.B.C.(D + 1)

• The first time a new function or type is exported from Liquid Fixpoint, if any of the components B, or C are missing, they shall be added and set to 0. Then the C component shall be incremented by 1, and the D component shall stripped. The version of Liquid Fixpoint is now A.B.(C + 1)

• The first time the signature of an exported function or type is changed, or an exported function or type is removed (this includes functions or types that Liquid Fixpoint re-exports from its own dependencies), if the B component is missing, it shall be added and set to 0. Then the B component shall be incremented by 1, and the C and D components shall be stripped. The version of Liquid Fixpoint is now A.(B + 1)

• The A component shall be updated at the sole discretion of the project owners.

It is recommended to use the Bumper utility to manage the versioning of Liquid Fixpoint. Bumper will automatically do the correct update to the cabal file. Additionally, it will update any packages that you have the source for that depend on Liquid Fixpoint.

To update Liquid Fixpoint and Liquid Haskell, first clone Liquid Haskell and Liquid Fixpoint to a common location:

git clone https://github.com/ucsd-progsys/liquidhaskell.git
git clone https://github.com/ucsd-progsys/liquid-fixpoint.git

To increment the D component of Liquid Fixpoint:

./path/to/bumper -3 liquid-fixpoint

This will update the D component of Liquid Fixpoint. If necessary, this will update the Build-Depends of Liquid Haskell. If the Build-Depends was updated, Liquid Haskell's D component will be incremented.

To increment the C component of Liquid Fixpoint, and strip the D component:

./path/to/bumper --minor liquid-fixpoint

As before, this will update Liquid Fixpoint and, if necessary, Liquid Haskell.

To increment the B component of Liquid Fixpoint, and strip the D and C components:

./path/to/bumper --major liquid-fixpoint

As before, this will update Liquid Fixpoint and, if necessary, Liquid Haskell

SMTLIB2 Interface

There is a new SMTLIB2 interface directly from Haskell:

• Language.Fixpoint.SmtLib2

See tests/smt2/{Smt.hs, foo.smt2} for an example of how to use it.

Options

--higherorder allows higher order binders into the environment

--extsolver runs the deprecated external solver.

--parts Partitions an FInfo into a [FInfo] and emits a bunch of files. So:

$ fixpoint -n -p path/to/foo.fq

will now emit files:

path/to/.liquid/foo.1.fq
path/to/.liquid/foo.2.fq
. . .
path/to/.liquid/foo.k.fq

and also a dot file with the constraint dependency graph:

path/to/.liquid/foo.fq.dot