diff --git a/.github/workflows/ci.yml b/.github/workflows/Cabal.yml
similarity index 99%
rename from .github/workflows/ci.yml
rename to .github/workflows/Cabal.yml
index 106b8adc8..1cf8e6a95 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/Cabal.yml
@@ -1,5 +1,5 @@
 # modified from https://github.com/jgm/pandoc/blob/master/.github/workflows/ci.yml
-name: CI
+name: Cabal
 
 on:
   push:
diff --git a/.github/workflows/Nix.yml b/.github/workflows/Nix.yml
new file mode 100644
index 000000000..8bc382119
--- /dev/null
+++ b/.github/workflows/Nix.yml
@@ -0,0 +1,27 @@
+name: Nix
+
+on:
+  push:
+    branches:
+    - '**'
+    paths-ignore: []
+  pull_request:
+    paths-ignore: []
+
+jobs:
+  linux:
+
+    runs-on: ubuntu-20.04
+    strategy:
+      fail-fast: false
+    steps:
+    - uses: actions/checkout@v2
+
+    # https://github.com/marketplace/actions/install-nix
+    - name: Install Nix
+      uses: cachix/install-nix-action@v14
+      with:
+        extra_nix_config: |
+          trusted-public-keys = hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
+          substituters = https://hydra.iohk.io https://cache.nixos.org/
+    - run: nix build --extra-experimental-features nix-command -f default.nix
diff --git a/README.md b/README.md
index c127b74f7..b24c33101 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,8 @@ CodeWorld
 =========
 
 [![Build Status](https://travis-ci.org/google/codeworld.svg?branch=master)](https://travis-ci.org/google/codeworld)
-[![Build status](https://github.com/google/codeworld/actions/workflows/ci.yml/badge.svg)](https://github.com/google/codeworld/actions/workflows/ci.yml)
+[![Build status](https://github.com/google/codeworld/actions/workflows/Cabal.yml/badge.svg)](https://github.com/google/codeworld/actions/workflows/Cabal.yml)
+[![Build status](https://github.com/google/codeworld/actions/workflows/Nix.yml/badge.svg)](https://github.com/google/codeworld/actions/workflows/Nix.yml)
 
 CodeWorld is an educational environment using Haskell. It provides a simple
 mathematical model for geometric figures, animations, and interactive and
diff --git a/cabal.project b/cabal.project
index 9466eccf8..0764876ae 100644
--- a/cabal.project
+++ b/cabal.project
@@ -1,12 +1,32 @@
+profiling: false
 packages:
   codeworld-account/
   codeworld-api/
   codeworld-auth/
+  -- codeworld-available-pkgs/
+  codeworld-base/
   codeworld-compiler/
   codeworld-error-sanitizer/
   codeworld-game-api/
   codeworld-game-server/
   codeworld-prediction/
   codeworld-server/
-  codeworld-base/
   funblocks-client/
+
+source-repository-package
+  type: git
+  location: https://github.com/peterbecich/hgeometry.git
+  tag: f898c5580c609320f0c7cc776e80f609711d19c5
+  subdir: hgeometry
+  --sha256: 0bmcb3dh1sfz6k7i30czcqqvarm1mzn55xdnimpnp19kj8v5g8nj
+
+source-repository-package
+  type: git
+  location: https://github.com/peterbecich/hgeometry.git
+  tag: f898c5580c609320f0c7cc776e80f609711d19c5
+  subdir: hgeometry-combinatorial
+  --sha256: 0bmcb3dh1sfz6k7i30czcqqvarm1mzn55xdnimpnp19kj8v5g8nj
+  
+allow-newer:
+    reflex:witherable
+  , patch:witherable
\ No newline at end of file
diff --git a/codeworld-api/codeworld-api.cabal b/codeworld-api/codeworld-api.cabal
index a7f731030..2de3b8cbf 100644
--- a/codeworld-api/codeworld-api.cabal
+++ b/codeworld-api/codeworld-api.cabal
@@ -61,11 +61,11 @@ Library
                        mtl                  >= 2.2.1 && < 2.3,
                        random               >= 1.1   && < 1.2,
                        ref-tf               >= 0.4   && < 0.5,
-                       reflex               >= 0.6.3 && < 0.7,
+                       reflex               >= 0.6.3,
                        template-haskell     >= 2.8   && < 2.18,
                        text                 >= 1.2.2 && < 1.3,
                        time                 >= 1.8   && < 2.0,
-                       witherable           >= 0.3   && < 0.4
+                       witherable           >= 0.3
 
   if impl(ghcjs)
     Js-sources:        jsbits/sim_fp.js
@@ -73,7 +73,7 @@ Library
                        ghcjs-prim,
                        codeworld-game-api,
                        codeworld-prediction,
-                       ghcjs-dom             >= 0.9 && < 0.9.4,
+                       ghcjs-dom             >= 0.9,
                        transformers
   else
     Build-depends:     blank-canvas          >= 0.6 && < 0.8,
@@ -122,11 +122,11 @@ Test-suite unit-tests
                        mtl                  >= 2.2.1 && < 2.3,
                        random               >= 1.1   && < 1.2,
                        ref-tf               >= 0.4   && < 0.5,
-                       reflex               >= 0.6.3 && < 0.7,
+                       reflex               >= 0.6.3,
                        template-haskell     >= 2.8   && < 2.18,
                        text                 >= 1.2.2 && < 1.3,
                        time                 >= 1.8   && < 2.0,
-                       witherable           >= 0.3   && < 0.4
+                       witherable           >= 0.3
 
   if impl(ghcjs)
     Js-sources:        jsbits/sim_fp.js
@@ -134,7 +134,7 @@ Test-suite unit-tests
                        ghcjs-prim,
                        codeworld-game-api,
                        codeworld-prediction,
-                       ghcjs-dom             >= 0.9 && < 0.9.4,
+                       ghcjs-dom             >= 0.9,
                        transformers
   else
     Build-depends:     blank-canvas          >= 0.6 && < 0.8,
diff --git a/codeworld-available-pkgs/codeworld-available-pkgs.cabal b/codeworld-available-pkgs/codeworld-available-pkgs.cabal
index bf9c4fca3..9a1593736 100644
--- a/codeworld-available-pkgs/codeworld-available-pkgs.cabal
+++ b/codeworld-available-pkgs/codeworld-available-pkgs.cabal
@@ -10,317 +10,630 @@ Copyright:           (c) 2020, The CodeWorld Authors
 Bug-reports:         https://github.com/google/codeworld/issues
 
 Library
-  Build-depends:
-    Boolean,
-    Decimal,
-    Earley,
-    HUnit,
-    ListLike,
-    MemoTrie,
-    MonadRandom,
-    NumInstances,
-    Only,
-    QuickCheck,
-    SHA,
-    StateVar,
-    Yampa,
-    active,
-    ad,
-    adjunctions,
-    -- accelerate, (does not build with GHCJS)
-    aeson,
-    algebraic-graphs,
-    apportionment,
-    array,
-    assoc,
-    async,
-    attoparsec,
-    attoparsec-iso8601,
-    auto,
-    -- axiom, (depends on transient, which fails to build)
-    backprop,
-    base,
-    base-compat-batteries,
-    base-orphans,
-    base64-bytestring,
-    basement,
-    bifunctors,
-    bimap,
-    binary,
-    binary-orphans,
-    blaze-builder,
-    blaze-html,
-    blaze-markup,
-    -- board-games, (depends on network)
-    bool8,
-    bytes,
-    bytestring,
-    bytestring-builder,
-    call-stack,
-    capability,
-    case-insensitive,
-    cereal,
-    cereal-text,
-    charset,
-    checksum,
-    circle-packing,
-    clock,
-    colour,
-    combinatorial,
-    comonad,
-    comonad-transformers,
-    concur-core,
-    concurrency,
-    concurrent-output,
-    conduit,
-    constraints,
-    constraints-extras,
-    containers,
-    contravariant,
-    cookie,
-    cryptonite,
-    cubicbezier,
-    data-accessor,
-    data-accessor-transformers,
-    data-default,
-    data-default-class,
-    data-default-instances-containers,
-    data-default-instances-dlist,
-    data-default-instances-old-locale,
-    data-reify,
-    dec,
-    deepseq,
-    dejafu,
-    dense-linear-algebra,
-    dependent-map,
-    dependent-sum,
-    diagrams,
-    diagrams-contrib,
-    diagrams-core,
-    diagrams-lib,
-    diagrams-solve,
-    diagrams-svg,
-    digestive-functors,
-    distributive,
-    dlist,
-    dsp,
-    dual-tree,
-    dunai,
-    either,
-    enclosed-exceptions,
-    enummapset,
-    erf,
-    event-list,
-    exception-transformers,
-    exceptions,
-    explicit-exception,
-    extensible-effects,
-    extra,
-    fail,
-    fast-math,
-    fclabels,
-    fgl,
-    fingertree,
-    finite-typelits,
-    first-class-families,
-    fixed-length,
-    fixed-list,
-    flow,
-    foldl,
-    fmlist,
-    force-layout,
-    -- formattable, (time dependency is too old)
-    -- foundation, (doesn't build for unclear reasons related to ghc-prim)
-    free,
-    fused-effects,
-    generic-deriving,
-    generic-lens,
-    generics-sop,
-    ghc-prim,
-    ghcjs-base,
-    ghcjs-dom,
-    ghcjs-perch,
-    ghcjs-prim,
-    gray-code,
-    groups,
-    half,
-    -- hamilton, (depends on hmatrix, which uses native libs)
-    hashable,
-    hashtables,
-    haskell-lexer,
-    haskell-src-exts,
-    haskell-src-meta,
-    hedgehog,
-    hgeometry >= 0.12,
-    hspec,
-    hspec-core,
-    hspec-expectations,
-    html,
-    http-api-data,
-    http-media,
-    http-types,
-    ieee754,
-    indexed-list-literals,
-    indexed-profunctors,
-    integer-gmp,
-    integer-logarithms,
-    integration,
-    interpolation,
-    intervals,
-    invariant,
-    jsaddle,
-    kan-extensions,
-    keycode,
-    latex,
-    leancheck,
-    lens,
-    lifted-async,
-    lifted-base,
-    linear,
-    log-domain,
-    logict,
-    loop,
-    markov-chain,
-    massiv,
-    math-functions,
-    matrix,
-    megaparsec,
-    memory,
-    mersenne-random-pure64,
-    mfsolve,
-    microlens,
-    microlens-mtl,
-    miso,
-    mmorph,
-    monad-bayes,
-    monad-control,
-    -- monad-coroutine 0.9.1 broken for old base
-    monad-coroutine < 0.9.1,
-    monad-loops,
-    monad-parallel,
-    monad-unlift,
-    mono-traversable,
-    monoid-extras,
-    monoid-transformer,
-    monoidal-containers,
-    moo,
-    mtl,
-    mtl-compat,
-    mutable-containers,
-    mwc-probability,
-    mwc-random,
-    nats,
-    natural-transformation,
-    netwire,
-    network-uri,
-    newtype-generics,
-    non-negative,
-    numeric-prelude,
-    old-locale,
-    optics,
-    optics-core,
-    optics-extra,
-    optparse-applicative,
-    parallel,
-    parsec,
-    parser-combinators,
-    parsers,
-    patch,
-    pipes,
-    polysemy,
-    pqueue,
-    prelude-compat,
-    pretty,
-    pretty-simple,
-    pretty-show,
-    prettyprinter,
-    prim-uniq,
-    primitive,
-    probability,
-    profunctors,
-    protolude,
-    psqueues,
-    quickcheck-io,
-    random,
-    random-shuffle,
-    reactive-banana,
-    -- reanimate, (depends on chiphunk, which depends on native library)
-    reducers,
-    ref-tf,
-    reflection,
-    reflex,
-    reflex-dom,
-    reflex-dom-core,
-    regex-base,
-    regex-compat-tdfa,
-    regex-tdfa,
-    relude,
-    resourcet,
-    rio,
-    safe,
-    safe-exceptions,
-    scheduler,
-    scientific,
-    semialign,
-    semigroupoids,
-    semigroups,
-    servant,
-    set-cover,
-    singleton-bool,
-    -- singletons, (build error related to Int/Integer/Uniq)
-    smallcheck,
-    sop-core,
-    split,
-    splitmix,
-    statistics,
-    stm,
-    storable-complex,
-    storable-record,
-    streaming,
-    string-conversions,
-    svg-builder,
-    syb,
-    tagged,
-    tasty,
-    tasty-expected-failure,
-    tasty-hedgehog,
-    tasty-hunit,
-    template-haskell,
-    text,
-    tf-random,
-    tfp,
-    these,
-    time,
-    time-compat,
-    transformers,
-    transformers-base,
-    transformers-compat,
-    -- transient, (build fails: missing Semigroup instance for TransIO)
-    trifecta,
-    type-equality,
-    typelits-witnesses,
-    unagi-chan,
-    unbounded-delays,
-    unexceptionalio,
-    unicode,
-    unique,
-    unliftio,
-    unliftio-core,
-    unordered-containers,
-    utf8-string,
-    utility-ht,
-    uuid-types,
-    vault,
-    vector,
-    vector-algorithms,
-    vector-binary-instances,
-    vector-builder,
-    vector-space,
-    vinyl,
-    void,
-    witherable,
-    wl-pprint-annotated,
-    zenc
+  extra-libraries: m
+  if impl(ghcjs -any)
+    Build-depends:
+      Boolean,
+      Decimal,
+      Earley,
+      HUnit,
+      ListLike,
+      MemoTrie,
+      MonadRandom,
+      NumInstances,
+      Only,
+      QuickCheck,
+      SHA,
+      StateVar,
+      Yampa,
+      active,
+      ad,
+      adjunctions,
+      -- accelerate, (does not build with GHCJS)
+      aeson,
+      algebraic-graphs,
+      apportionment,
+      array,
+      assoc,
+      async,
+      attoparsec,
+      attoparsec-iso8601,
+      auto,
+      -- axiom, (depends on transient, which fails to build)
+      backprop,
+      base,
+      base-compat-batteries,
+      base-orphans,
+      base64-bytestring,
+      basement,
+      bifunctors,
+      bimap,
+      binary,
+      binary-orphans,
+      blaze-builder,
+      blaze-html,
+      blaze-markup,
+      -- board-games, (depends on network)
+      bool8,
+      bytes,
+      bytestring,
+      bytestring-builder,
+      call-stack,
+      capability,
+      case-insensitive,
+      cereal,
+      cereal-text,
+      charset,
+      checksum,
+      circle-packing,
+      clock,
+      colour,
+      combinatorial,
+      comonad,
+      comonad-transformers,
+      concur-core,
+      concurrency,
+      concurrent-output,
+      conduit,
+      constraints,
+      constraints-extras,
+      containers,
+      contravariant,
+      cookie,
+      cryptonite,
+      cubicbezier,
+      data-accessor,
+      data-accessor-transformers,
+      data-default,
+      data-default-class,
+      data-default-instances-containers,
+      data-default-instances-dlist,
+      data-default-instances-old-locale,
+      data-reify,
+      dec,
+      deepseq,
+      dejafu,
+      dense-linear-algebra,
+      dependent-map,
+      dependent-sum,
+      diagrams,
+      diagrams-contrib,
+      diagrams-core,
+      diagrams-lib,
+      diagrams-solve,
+      diagrams-svg,
+      digestive-functors,
+      distributive,
+      dlist,
+      dsp,
+      dual-tree,
+      dunai,
+      either,
+      enclosed-exceptions,
+      enummapset,
+      erf,
+      event-list,
+      exception-transformers,
+      exceptions,
+      explicit-exception,
+      extensible-effects,
+      extra,
+      fail,
+      fast-math,
+      fclabels,
+      fgl,
+      fingertree,
+      finite-typelits,
+      first-class-families,
+      fixed-length,
+      fixed-list,
+      flow,
+      foldl,
+      fmlist,
+      force-layout,
+      -- formattable, (time dependency is too old)
+      -- foundation, (doesn't build for unclear reasons related to ghc-prim)
+      free,
+      fused-effects,
+      generic-deriving,
+      generic-lens,
+      generics-sop,
+      ghc-prim,
+      ghcjs-base,
+      ghcjs-dom,
+      ghcjs-perch,
+      ghcjs-prim,
+      gray-code,
+      groups,
+      half,
+      -- hamilton, (depends on hmatrix, which uses native libs)
+      hashable,
+      hashtables,
+      haskell-lexer,
+      haskell-src-exts,
+      haskell-src-meta,
+      hedgehog,
+      hgeometry >= 0.12,
+      hspec,
+      hspec-core,
+      hspec-expectations,
+      html,
+      http-api-data,
+      http-media,
+      http-types,
+      ieee754,
+      indexed-list-literals,
+      indexed-profunctors,
+      integer-gmp,
+      integer-logarithms,
+      integration,
+      interpolation,
+      intervals,
+      invariant,
+      jsaddle,
+      kan-extensions,
+      keycode,
+      latex,
+      leancheck,
+      lens,
+      lifted-async,
+      lifted-base,
+      linear,
+      log-domain,
+      logict,
+      loop,
+      markov-chain,
+      massiv,
+      math-functions,
+      matrix,
+      megaparsec,
+      memory,
+      mersenne-random-pure64,
+      mfsolve,
+      microlens,
+      microlens-mtl,
+      miso,
+      mmorph,
+      monad-bayes,
+      monad-control,
+      -- monad-coroutine 0.9.1 broken for old base
+      monad-coroutine < 0.9.1,
+      monad-loops,
+      monad-parallel,
+      monad-unlift,
+      mono-traversable,
+      monoid-extras,
+      monoid-transformer,
+      monoidal-containers,
+      moo,
+      mtl,
+      mtl-compat,
+      mutable-containers,
+      mwc-probability,
+      mwc-random,
+      nats,
+      natural-transformation,
+      netwire,
+      network-uri,
+      newtype-generics,
+      non-negative,
+      numeric-prelude,
+      old-locale,
+      optics,
+      optics-core,
+      optics-extra,
+      optparse-applicative,
+      parallel,
+      parsec,
+      parser-combinators,
+      parsers,
+      patch,
+      pipes,
+      polysemy,
+      pqueue,
+      prelude-compat,
+      pretty,
+      pretty-simple,
+      pretty-show,
+      prettyprinter,
+      prim-uniq,
+      primitive,
+      probability,
+      profunctors,
+      protolude,
+      psqueues,
+      quickcheck-io,
+      random,
+      random-shuffle,
+      reactive-banana,
+      -- reanimate, (depends on chiphunk, which depends on native library)
+      reducers,
+      ref-tf,
+      reflection,
+      reflex,
+      reflex-dom,
+      reflex-dom-core,
+      regex-base,
+      regex-compat-tdfa,
+      regex-tdfa,
+      relude,
+      resourcet,
+      rio,
+      safe,
+      safe-exceptions,
+      scheduler,
+      scientific,
+      semialign,
+      semigroupoids,
+      semigroups,
+      servant,
+      set-cover,
+      singleton-bool,
+      -- singletons, (build error related to Int/Integer/Uniq)
+      smallcheck,
+      sop-core,
+      split,
+      splitmix,
+      statistics,
+      stm,
+      storable-complex,
+      storable-record,
+      streaming,
+      string-conversions,
+      svg-builder,
+      syb,
+      tagged,
+      tasty,
+      tasty-expected-failure,
+      tasty-hedgehog,
+      tasty-hunit,
+      template-haskell,
+      text,
+      tf-random,
+      tfp,
+      these,
+      time,
+      time-compat,
+      transformers,
+      transformers-base,
+      transformers-compat,
+      -- transient, (build fails: missing Semigroup instance for TransIO)
+      trifecta,
+      type-equality,
+      typelits-witnesses,
+      unagi-chan,
+      unbounded-delays,
+      unexceptionalio,
+      unicode,
+      unique,
+      unliftio,
+      unliftio-core,
+      unordered-containers,
+      utf8-string,
+      utility-ht,
+      uuid-types,
+      vault,
+      vector,
+      vector-algorithms,
+      vector-binary-instances,
+      vector-builder,
+      vector-space,
+      vinyl,
+      void,
+      witherable,
+      wl-pprint-annotated,
+      zenc
+  else
+    -- excludes ghcjs-base and ghcjs-prim
+    Build-depends:
+      Boolean,
+      Decimal,
+      Earley,
+      HUnit,
+      ListLike,
+      MemoTrie,
+      MonadRandom,
+      NumInstances,
+      Only,
+      QuickCheck,
+      SHA,
+      StateVar,
+      Yampa,
+      active,
+      ad,
+      adjunctions,
+      -- accelerate, (does not build with GHCJS)
+      aeson,
+      algebraic-graphs,
+      apportionment,
+      array,
+      assoc,
+      async,
+      attoparsec,
+      attoparsec-iso8601,
+      auto,
+      -- axiom, (depends on transient, which fails to build)
+      backprop,
+      base,
+      base-compat-batteries,
+      base-orphans,
+      base64-bytestring,
+      basement,
+      bifunctors,
+      bimap,
+      binary,
+      binary-orphans,
+      blaze-builder,
+      blaze-html,
+      blaze-markup,
+      -- board-games, (depends on network)
+      bool8,
+      bytes,
+      bytestring,
+      bytestring-builder,
+      call-stack,
+      capability,
+      case-insensitive,
+      cereal,
+      cereal-text,
+      charset,
+      checksum,
+      circle-packing,
+      clock,
+      colour,
+      combinatorial,
+      comonad,
+      comonad-transformers,
+      concur-core,
+      concurrency,
+      concurrent-output,
+      conduit,
+      constraints,
+      constraints-extras,
+      containers,
+      contravariant,
+      cookie,
+      cryptonite,
+      cubicbezier,
+      data-accessor,
+      data-accessor-transformers,
+      data-default,
+      data-default-class,
+      data-default-instances-containers,
+      data-default-instances-dlist,
+      data-default-instances-old-locale,
+      data-reify,
+      dec,
+      deepseq,
+      dejafu,
+      dense-linear-algebra,
+      dependent-map,
+      dependent-sum,
+      diagrams,
+      diagrams-contrib,
+      diagrams-core,
+      diagrams-lib,
+      diagrams-solve,
+      diagrams-svg,
+      digestive-functors,
+      distributive,
+      dlist,
+      dsp,
+      dual-tree,
+      dunai,
+      either,
+      enclosed-exceptions,
+      enummapset,
+      erf,
+      event-list,
+      exception-transformers,
+      exceptions,
+      explicit-exception,
+      extensible-effects,
+      extra,
+      fail,
+      fast-math,
+      fclabels,
+      fgl,
+      fingertree,
+      finite-typelits,
+      first-class-families,
+      fixed-length,
+      fixed-list,
+      flow,
+      foldl,
+      fmlist,
+      force-layout,
+      -- formattable, (time dependency is too old)
+      -- foundation, (doesn't build for unclear reasons related to ghc-prim)
+      free,
+      fused-effects,
+      generic-deriving,
+      generic-lens,
+      generics-sop,
+      ghc-prim,
+      ghcjs-dom,
+      ghcjs-perch,
+      gray-code,
+      groups,
+      half,
+      -- hamilton, (depends on hmatrix, which uses native libs)
+      hashable,
+      hashtables,
+      haskell-lexer,
+      haskell-src-exts,
+      haskell-src-meta,
+      hedgehog,
+      hgeometry >= 0.12,
+      hspec,
+      hspec-core,
+      hspec-expectations,
+      html,
+      http-api-data,
+      http-media,
+      http-types,
+      ieee754,
+      indexed-list-literals,
+      indexed-profunctors,
+      integer-gmp,
+      integer-logarithms,
+      integration,
+      interpolation,
+      intervals,
+      invariant,
+      jsaddle,
+      kan-extensions,
+      keycode,
+      latex,
+      leancheck,
+      lens,
+      lifted-async,
+      lifted-base,
+      linear,
+      log-domain,
+      logict,
+      loop,
+      markov-chain,
+      massiv,
+      math-functions,
+      matrix,
+      megaparsec,
+      memory,
+      mersenne-random-pure64,
+      mfsolve,
+      microlens,
+      microlens-mtl,
+      miso,
+      mmorph,
+      monad-bayes,
+      monad-control,
+      -- monad-coroutine 0.9.1 broken for old base
+      monad-coroutine < 0.9.1,
+      monad-loops,
+      monad-parallel,
+      monad-unlift,
+      mono-traversable,
+      monoid-extras,
+      monoid-transformer,
+      monoidal-containers,
+      moo,
+      mtl,
+      mtl-compat,
+      mutable-containers,
+      mwc-probability,
+      mwc-random,
+      nats,
+      natural-transformation,
+      netwire,
+      network-uri,
+      newtype-generics,
+      non-negative,
+      numeric-prelude,
+      old-locale,
+      optics,
+      optics-core,
+      optics-extra,
+      optparse-applicative,
+      parallel,
+      parsec,
+      parser-combinators,
+      parsers,
+      patch,
+      pipes,
+      polysemy,
+      pqueue,
+      prelude-compat,
+      pretty,
+      pretty-simple,
+      pretty-show,
+      prettyprinter,
+      prim-uniq,
+      primitive,
+      probability,
+      profunctors,
+      protolude,
+      psqueues,
+      quickcheck-io,
+      random,
+      random-shuffle,
+      reactive-banana,
+      -- reanimate, (depends on chiphunk, which depends on native library)
+      reducers,
+      ref-tf,
+      reflection,
+      reflex,
+      reflex-dom,
+      reflex-dom-core,
+      regex-base,
+      regex-compat-tdfa,
+      regex-tdfa,
+      relude,
+      resourcet,
+      rio,
+      safe,
+      safe-exceptions,
+      scheduler,
+      scientific,
+      semialign,
+      semigroupoids,
+      semigroups,
+      servant,
+      set-cover,
+      singleton-bool,
+      -- singletons, (build error related to Int/Integer/Uniq)
+      smallcheck,
+      sop-core,
+      split,
+      splitmix,
+      statistics,
+      stm,
+      storable-complex,
+      storable-record,
+      streaming,
+      string-conversions,
+      svg-builder,
+      syb,
+      tagged,
+      tasty,
+      tasty-expected-failure,
+      tasty-hedgehog,
+      tasty-hunit,
+      template-haskell,
+      text,
+      tf-random,
+      tfp,
+      these,
+      time,
+      time-compat,
+      transformers,
+      transformers-base,
+      transformers-compat,
+      -- transient, (build fails: missing Semigroup instance for TransIO)
+      trifecta,
+      type-equality,
+      typelits-witnesses,
+      unagi-chan,
+      unbounded-delays,
+      unexceptionalio,
+      unicode,
+      unique,
+      unliftio,
+      unliftio-core,
+      unordered-containers,
+      utf8-string,
+      utility-ht,
+      uuid-types,
+      vault,
+      vector,
+      vector-algorithms,
+      vector-binary-instances,
+      vector-builder,
+      vector-space,
+      vinyl,
+      void,
+      witherable,
+      wl-pprint-annotated,
+      zenc
 
   Default-language:    Haskell2010
 
diff --git a/codeworld-base/codeworld-base.cabal b/codeworld-base/codeworld-base.cabal
index 3f478f405..d9aaeb3ab 100644
--- a/codeworld-base/codeworld-base.cabal
+++ b/codeworld-base/codeworld-base.cabal
@@ -45,7 +45,7 @@ Library
                          codeworld-api,
                          ghc-prim,
                          ghcjs-base,
-                         ghcjs-dom,
+                         ghcjs-dom >=0.9,
                          mtl,
                          random,
                          random-shuffle,
diff --git a/codeworld-compiler/codeworld-compiler.cabal b/codeworld-compiler/codeworld-compiler.cabal
index 75ed47614..0033f98b1 100644
--- a/codeworld-compiler/codeworld-compiler.cabal
+++ b/codeworld-compiler/codeworld-compiler.cabal
@@ -54,16 +54,17 @@ Library
     directory,
     exceptions,
     filepath,
-    ghc == 8.6.5,
-    ghc-boot-th == 8.6.5,
+    ghc,
+    ghc-boot,
+    ghc-boot-th,
     hashable,
     haskell-src-exts >= 1.20,
     megaparsec >= 7.0.0 && < 8.0.0,
     memory,
     mtl,
     process,
+    regex-base,
     regex-tdfa,
-    regex-tdfa-text,
     split,
     syb,
     temporary,
diff --git a/codeworld-error-sanitizer/codeworld-error-sanitizer.cabal b/codeworld-error-sanitizer/codeworld-error-sanitizer.cabal
index 95ad875b1..8940b32f7 100644
--- a/codeworld-error-sanitizer/codeworld-error-sanitizer.cabal
+++ b/codeworld-error-sanitizer/codeworld-error-sanitizer.cabal
@@ -25,8 +25,7 @@ Library
   else
     Build-depends:     array,
                        regex-base,
-                       regex-tdfa,
-                       regex-tdfa-text
+                       regex-tdfa
 
   Default-language:    Haskell2010
   Exposed: True
@@ -49,7 +48,6 @@ Test-suite unit-tests
   else
     Build-depends:     array,
                        regex-base,
-                       regex-tdfa,
-                       regex-tdfa-text
+                       regex-tdfa
 
   Default-language:    Haskell2010
diff --git a/codeworld-requirements/codeworld-requirements.cabal b/codeworld-requirements/codeworld-requirements.cabal
index 3337ab1ed..f2c09c324 100644
--- a/codeworld-requirements/codeworld-requirements.cabal
+++ b/codeworld-requirements/codeworld-requirements.cabal
@@ -36,8 +36,8 @@ library
                        haskell-src-exts >= 1.20,
                        mtl,
                        process,
+                       regex-base,
                        regex-tdfa,
-                       regex-tdfa-text,
                        syb,
                        temporary,
                        text,
diff --git a/codeworld-server/codeworld-server.cabal b/codeworld-server/codeworld-server.cabal
index 035e6a683..d9cb09fd9 100644
--- a/codeworld-server/codeworld-server.cabal
+++ b/codeworld-server/codeworld-server.cabal
@@ -39,7 +39,7 @@ Executable codeworld-server
     fast-logger,
     filelock,
     filepath,
-    haskell-src-exts < 1.21,
+    haskell-src-exts,
     http-conduit,
     lifted-base,
     memory,
diff --git a/default.nix b/default.nix
new file mode 100644
index 000000000..b079a9792
--- /dev/null
+++ b/default.nix
@@ -0,0 +1,34 @@
+# https://input-output-hk.github.io/haskell.nix/tutorials/getting-started/
+{ compiler ? "ghc865",
+  ghcjsVersion ? "8.6.0.0.10",
+  ghcVersion ? "8.6.5",
+  withCoverage ? false
+}:
+  let
+    sources = import ./nix/sources.nix {};
+    haskellNix = import sources.haskellNix {};
+    pkgs = import
+      haskellNix.sources.nixpkgs-unstable
+      haskellNix.nixpkgsArgs;
+      overlays = [
+        (self: super:
+          {
+            m = self.stdenv.mkDerivation {
+              name = "m";
+              unpackPhase = "true";
+              installPhase = "mkdir -p $out";
+            };
+          }
+        )
+      ];
+
+  in
+    pkgs.haskell-nix.ghcjsProject {
+      # projectFileName = "cabal.project";
+      ghcjsVersion = "8.6.0.0.10";
+      src = pkgs.haskell-nix.haskellLib.cleanGit {
+        name = "codeworld";
+        src = ./.;
+      };
+      compiler-nix-name = compiler;
+    }
diff --git a/funblocks-client/funblocks-client.cabal b/funblocks-client/funblocks-client.cabal
index c5f50adea..6c9abb9bf 100644
--- a/funblocks-client/funblocks-client.cabal
+++ b/funblocks-client/funblocks-client.cabal
@@ -38,11 +38,11 @@ Executable funblocks-client
     Build-depends:       ghcjs-base,
                          text,
                          containers,
-                         ghcjs-dom,
+                         ghcjs-dom >=0.9,
                          mtl
   else
     Build-depends:       ghcjs-base-stub,
                          text,
                          containers,
-                         ghcjs-dom,
+                         ghcjs-dom >=0.9,
                          mtl
diff --git a/nix/sources.json b/nix/sources.json
new file mode 100644
index 000000000..e8393e221
--- /dev/null
+++ b/nix/sources.json
@@ -0,0 +1,38 @@
+{
+    "haskellNix": {
+        "branch": "master",
+        "description": "Alternative Haskell Infrastructure for Nixpkgs",
+        "homepage": "https://input-output-hk.github.io/haskell.nix",
+        "owner": "input-output-hk",
+        "repo": "haskell.nix",
+        "rev": "564458fc4080c0fc51e316d74c3dbb68639ea839",
+        "sha256": "0d7kp3sqw8zhp4sv5awla6ch15mbndmr3640y3pwlvkcb59p8amm",
+        "type": "tarball",
+        "url": "https://github.com/input-output-hk/haskell.nix/archive/564458fc4080c0fc51e316d74c3dbb68639ea839.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "niv": {
+        "branch": "master",
+        "description": "Easy dependency management for Nix projects",
+        "homepage": "https://github.com/nmattia/niv",
+        "owner": "nmattia",
+        "repo": "niv",
+        "rev": "65a61b147f307d24bfd0a5cd56ce7d7b7cc61d2e",
+        "sha256": "17mirpsx5wyw262fpsd6n6m47jcgw8k2bwcp1iwdnrlzy4dhcgqh",
+        "type": "tarball",
+        "url": "https://github.com/nmattia/niv/archive/65a61b147f307d24bfd0a5cd56ce7d7b7cc61d2e.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs": {
+        "branch": "release-20.03",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "eb73405ecceb1dc505b7cbbd234f8f94165e2696",
+        "sha256": "06k21wbyhhvq2f1xczszh3c2934p0m02by3l2ixvd6nkwrqklax7",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/eb73405ecceb1dc505b7cbbd234f8f94165e2696.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    }
+}
diff --git a/nix/sources.nix b/nix/sources.nix
new file mode 100644
index 000000000..1938409dd
--- /dev/null
+++ b/nix/sources.nix
@@ -0,0 +1,174 @@
+# This file has been generated by Niv.
+
+let
+
+  #
+  # The fetchers. fetch_<type> fetches specs of type <type>.
+  #
+
+  fetch_file = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchurl { inherit (spec) url sha256; name = name'; }
+      else
+        pkgs.fetchurl { inherit (spec) url sha256; name = name'; };
+
+  fetch_tarball = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchTarball { name = name'; inherit (spec) url sha256; }
+      else
+        pkgs.fetchzip { name = name'; inherit (spec) url sha256; };
+
+  fetch_git = name: spec:
+    let
+      ref =
+        if spec ? ref then spec.ref else
+          if spec ? branch then "refs/heads/${spec.branch}" else
+            if spec ? tag then "refs/tags/${spec.tag}" else
+              abort "In git source '${name}': Please specify `ref`, `tag` or `branch`!";
+    in
+      builtins.fetchGit { url = spec.repo; inherit (spec) rev; inherit ref; };
+
+  fetch_local = spec: spec.path;
+
+  fetch_builtin-tarball = name: throw
+    ''[${name}] The niv type "builtin-tarball" is deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=tarball -a builtin=true'';
+
+  fetch_builtin-url = name: throw
+    ''[${name}] The niv type "builtin-url" will soon be deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=file -a builtin=true'';
+
+  #
+  # Various helpers
+  #
+
+  # https://github.com/NixOS/nixpkgs/pull/83241/files#diff-c6f540a4f3bfa4b0e8b6bafd4cd54e8bR695
+  sanitizeName = name:
+    (
+      concatMapStrings (s: if builtins.isList s then "-" else s)
+        (
+          builtins.split "[^[:alnum:]+._?=-]+"
+            ((x: builtins.elemAt (builtins.match "\\.*(.*)" x) 0) name)
+        )
+    );
+
+  # The set of packages used when specs are fetched using non-builtins.
+  mkPkgs = sources: system:
+    let
+      sourcesNixpkgs =
+        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; }) { inherit system; };
+      hasNixpkgsPath = builtins.any (x: x.prefix == "nixpkgs") builtins.nixPath;
+      hasThisAsNixpkgsPath = <nixpkgs> == ./.;
+    in
+      if builtins.hasAttr "nixpkgs" sources
+      then sourcesNixpkgs
+      else if hasNixpkgsPath && ! hasThisAsNixpkgsPath then
+        import <nixpkgs> {}
+      else
+        abort
+          ''
+            Please specify either <nixpkgs> (through -I or NIX_PATH=nixpkgs=...) or
+            add a package called "nixpkgs" to your sources.json.
+          '';
+
+  # The actual fetching function.
+  fetch = pkgs: name: spec:
+
+    if ! builtins.hasAttr "type" spec then
+      abort "ERROR: niv spec ${name} does not have a 'type' attribute"
+    else if spec.type == "file" then fetch_file pkgs name spec
+    else if spec.type == "tarball" then fetch_tarball pkgs name spec
+    else if spec.type == "git" then fetch_git name spec
+    else if spec.type == "local" then fetch_local spec
+    else if spec.type == "builtin-tarball" then fetch_builtin-tarball name
+    else if spec.type == "builtin-url" then fetch_builtin-url name
+    else
+      abort "ERROR: niv spec ${name} has unknown type ${builtins.toJSON spec.type}";
+
+  # If the environment variable NIV_OVERRIDE_${name} is set, then use
+  # the path directly as opposed to the fetched source.
+  replace = name: drv:
+    let
+      saneName = stringAsChars (c: if isNull (builtins.match "[a-zA-Z0-9]" c) then "_" else c) name;
+      ersatz = builtins.getEnv "NIV_OVERRIDE_${saneName}";
+    in
+      if ersatz == "" then drv else
+        # this turns the string into an actual Nix path (for both absolute and
+        # relative paths)
+        if builtins.substring 0 1 ersatz == "/" then /. + ersatz else /. + builtins.getEnv "PWD" + "/${ersatz}";
+
+  # Ports of functions for older nix versions
+
+  # a Nix version of mapAttrs if the built-in doesn't exist
+  mapAttrs = builtins.mapAttrs or (
+    f: set: with builtins;
+    listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set))
+  );
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/lists.nix#L295
+  range = first: last: if first > last then [] else builtins.genList (n: first + n) (last - first + 1);
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L257
+  stringToCharacters = s: map (p: builtins.substring p 1 s) (range 0 (builtins.stringLength s - 1));
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L269
+  stringAsChars = f: s: concatStrings (map f (stringToCharacters s));
+  concatMapStrings = f: list: concatStrings (map f list);
+  concatStrings = builtins.concatStringsSep "";
+
+  # https://github.com/NixOS/nixpkgs/blob/8a9f58a375c401b96da862d969f66429def1d118/lib/attrsets.nix#L331
+  optionalAttrs = cond: as: if cond then as else {};
+
+  # fetchTarball version that is compatible between all the versions of Nix
+  builtins_fetchTarball = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchTarball;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchTarball ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      else
+        fetchTarball attrs;
+
+  # fetchurl version that is compatible between all the versions of Nix
+  builtins_fetchurl = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchurl;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchurl ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      else
+        fetchurl attrs;
+
+  # Create the final "sources" from the config
+  mkSources = config:
+    mapAttrs (
+      name: spec:
+        if builtins.hasAttr "outPath" spec
+        then abort
+          "The values in sources.json should not have an 'outPath' attribute"
+        else
+          spec // { outPath = replace name (fetch config.pkgs name spec); }
+    ) config.sources;
+
+  # The "config" used by the fetchers
+  mkConfig =
+    { sourcesFile ? if builtins.pathExists ./sources.json then ./sources.json else null
+    , sources ? if isNull sourcesFile then {} else builtins.fromJSON (builtins.readFile sourcesFile)
+    , system ? builtins.currentSystem
+    , pkgs ? mkPkgs sources system
+    }: rec {
+      # The sources, i.e. the attribute set of spec name to spec
+      inherit sources;
+
+      # The "pkgs" (evaluated nixpkgs) to use for e.g. non-builtin fetchers
+      inherit pkgs;
+    };
+
+in
+mkSources (mkConfig {}) // { __functor = _: settings: mkSources (mkConfig settings); }