Summer of Haskell

Midterm update for 2017

Posted on August 4, 2017 by Niki Vazou & Jasper Van der Jeugt (permalink)

Hey all,

We’d like to update the wider Haskell community on the state of the Summer of Haskell projects, now that the midterm evaluation has passed. We are very happy that almost everyone passed the evaluation.

Although several of the students maintain blogs on their own (which we definitely encourage), we also made an attempt to compile the information here.

  1. Safe streaming with linear types
    Student: Edvard Hübinette
    Mentor: Arnaud Spiwack

    The majority of the streaming library internals and prelude is converted for leveraging linear types and uses a linear monad class to ensure that old stream states cannot be accessed again, effectively eliminating the issue with arbitrarily weird behaviour arising from duplicated effects.

    The student has also found some very tricky usability issues that arise from forcing linear consumption, which will be documented in an upcoming blog post.

    Other than that the student is working on implementing linear versions of other monads like State, and trying to figure out how to instance LMonad IO, which seems somewhat tricky.

  2. Bringing Sanity to the GHC Performance Test-Suite
    Student: Jared Weakly
    Mentor: Ben Gamari

    The creation of the tooling, writing the functionality, and all of the necessary supporting elements of the project are seemingly done.

    What remains at this point is to start actually wiring things together in a mock-up and then finally in production. Along the way, any missing functionality will be added, helping tools to streamline things will also be added, and so on.

  3. Haskell IDE Engine
    Student: Zubin Duggal
    Mentor: Alan Zimmerman

    HIE with the vscode plugin is now in a useable state and implements a large portion of the Language Server Protocol.

    More details can be found here:

  4. Last Mile for cabal new-build
    Student: Francesco Gazzetta
    Mentor: Daniel Wagner

    Almost all the basic new-build commands are implemented, and the student is working on new-exec now. A bunch of bugs have been fixed (e.g. datafiles for inplace builds). After new-exec, the student will work on the much-needed new-install, which will probably take most of the remaining time (see the design concept, #4558). The progress is tracked here:

  5. Totality checking base with Liquid Haskell
    Student: Sean Leffler
    Mentor: Niki Vazou
    Co-mentor: Eric Seidel

    So far, the student has identified multiple minor bugs and one major bug in Liquid Haskell.

    While the student hasn’t made great progress on actually verifying base, the project is turning into a research project after and a number of interesting ways have been identified in the ways that Liquid Haskell interacts with the particular style of code used in base - especially Haskell’s laziness.

  6. Modularizing haskell-mode and improving haskell-interactive-mode
    Student: Vasantha Ganesh Kanniappan
    Mentor: Gracjan Polak

    Status of the project: Comint based Major mode for ghci repl (Inf-haskell) is being improved. The student is in the middle of a number of things: converting the interactive-haskell-mode, the minor-mode that can be used along with haskell-mode for getting completion-at-point-functions, M-., loading module to interpreter, getting type of function at point and other features to depend on the comint based process instead of the old haskell-interactive-mode.

    More information can be found in this blogpost:

  7. Haskey (an embedded key-value store modeled after LMDB)
    Student: Henri Verroken
    Mentor: Steven Keuchel
    Co-mentor: George Karachalias

    The following things have been finished:

    • The pure B+tree implementation.
    • The impure B+tree implementation, which abstracts over an page allocation back-end.
    • An append-only page allocator, a page-reusing allocator, and a concurrent page allocator (allowing for concurrent readers and serialized writers), which we are currently heavily testing.
    • Transaction support.
    • An on-disk and in-memory storage engine.

    Currently missing for our MVP (and publishing of the key-value store) are overflow pages to store large values and an efficient binary serialization.

  8. Improve the Shake-Based Hadrian Build System for GHC
    Student: Zhen Zhang
    Mentor: Andrey Mokhov

    28 PRs have been merged up to now, and two out of three major goals (dynamic way support and installation rule) are implemented and tested on Linux and OS X platforms.

    Another major goal, cross-compilation support, is also being investigated in-depth. Besides the coding part, 29 issues have been submitted, and project board has been set up. A nightly build system & tracker, called Hadrian’s Wall, is launched as well. Our team will also talk about Hadrian in this year’s HIW at ICFP.

  9. GHC Performance improvements
    Student: Igor Popov
    Mentor: Jose Calderon

    Unfortunately, the student did not pass the midterm evaluation for this perhaps too ambitious project.

  10. Improvement of Hackage Matrix Builder
    Student: Andika Demas Riyandi
    Mentor: Herbert Valerio Riedel

    The migration of the site’s frontend to Purescript has been completed and soon be deployed.

    Before adding new feature, the API will be upgraded to use servant-purescript so frontend and backend communication will be conducted smoothly. The next features that are planned are extending the UI to allow accessing previous historic reports that are in the database and the ability to traverse package dependency graphs.

  11. WebGHC (a WebAssembly backend for GHC)
    Student: Michael Vogelsang
    Mentor: Will Fancher

    As it stands, WebGHC has solid foundations for building libc, compiler-rt, and ncurses to WebAssembly encoded via nix. It is possible to use the work to easily compile C code to working WebAssembly. The studnet and mentor are optimistic that they will be able to have something usable by the end of the work term.

We are very happy with the progress of the students so far and we hope that they continue to work diligently towards the final evaluation.

Summer of Haskell 2017 is made possible by our generous sponsors:

Davean has volunteered to fund a student expressly to work on the Hadrian build system for GHC. Steven Keuchel has provided funds for a student to work on Haskey.

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