diff --git a/.github/workflows/haskell.yml b/.github/workflows/haskell.yml
index 92d3748..bbf33cf 100644
--- a/.github/workflows/haskell.yml
+++ b/.github/workflows/haskell.yml
@@ -2,22 +2,18 @@ name: Haskell CI
 
 on:
   push:
-    branches:
-      - '*'
-  pull_request:
-    branches: [ "master" ]
+  workflow_dispatch:
 
 permissions:
   contents: read
 
 jobs:
   fourmolu:
-
     runs-on: ubuntu-latest
-  
+
     steps:
-      - uses: actions/checkout@v3
-      - uses: haskell-actions/run-fourmolu@v9
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: haskell-actions/run-fourmolu@3b7702b41516aa428dfe6e295dc73476ae58f69e # v11
         with:
           version: "0.14.0.0"
   build:
@@ -27,104 +23,58 @@ jobs:
       fail-fast: false
       matrix:
         os: [windows-latest, macos-latest, ubuntu-latest]
-        ghc-version: ['9.6', '9.4', '9.2', '9.0']
+        ghc-version: ["9.12", "9.10", "9.8", "9.6", "9.4", "9.2"]
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
 
       - name: Set up GHC ${{ matrix.ghc-version }}
-        uses: haskell/actions/setup@v2
+        uses: haskell-actions/setup@96f3dafd067155f32643c2a0757ab71d2910e2c2 # v2.8.0
         id: setup
         with:
           ghc-version: ${{ matrix.ghc-version }}
-          enable-stack: true
 
       - name: Installed minor versions of GHC, Cabal, and Stack
         shell: bash
         run: |
           GHC_VERSION=$(ghc --numeric-version)
           CABAL_VERSION=$(cabal --numeric-version)
-          STACK_VERSION=$(stack --numeric-version)
           echo "GHC_VERSION=${GHC_VERSION}"     >> "${GITHUB_ENV}"
           echo "CABAL_VERSION=${CABAL_VERSION}" >> "${GITHUB_ENV}"
-          echo "STACK_VERSION=${STACK_VERSION}" >> "${GITHUB_ENV}"
+
+      - name: Check cabal file
+        run: cabal check
 
       - name: Configure the build
         run: |
-          # cabal configure --enable-tests --enable-benchmarks --disable-documentation
-          # cabal build --dry-run
-          stack build --test --bench --no-haddock --dry-run
-        # The last step generates dist-newstyle/cache/plan.json for the cache key.
-
-      - name: Restore .stack-work cache
-        uses: actions/cache/restore@v3
-        id: cache-restore-stack-work
-        with:
-          path: .stack-work
-          key: ${{ runner.os }}-ghc-${{ env.GHC_VERSION }}-stack-${{ env.STACK_VERSION }}-stack-work-${{ hashFiles('stack.yaml') }}-${{ hashFiles('package.yaml') }}-${{ hashFiles('**/*.hs') }}
-          restore-keys: |
-            ${{ runner.os }}-ghc-${{ env.GHC_VERSION }}-stack-${{ env.STACK_VERSION }}-stack-work-
-      
-      - name: Restore ~/.stack cache (Unix)
-        uses: actions/cache/restore@v3
-        id: cache-restore-stack-global-unix
-        if: runner.os == 'Linux' || runner.os == 'macOS'
-        with:
-          path: ~/.stack
-          key: ${{ runner.os }}-ghc-${{ env.GHC_VERSION }}-stack-${{ env.STACK_VERSION }}-stack-global-${{ hashFiles('stack.yaml') }}-${{ hashFiles('package.yaml') }}
-          restore-keys: |
-            ${{ runner.os }}-ghc-${{ env.GHC_VERSION }}-stack-${{ env.STACK_VERSION }}-stack-global-
-
-      - name: Restore %APPDATA%\stack, %LOCALAPPDATA%\Programs\stack cache (Windows)
-        uses: actions/cache/restore@v3
-        id: cache-restore-stack-global-windows
-        if: runner.os == 'Windows'
+          cabal configure --enable-tests --enable-benchmarks --disable-documentation
+          cabal build --dry-run
+
+      - name: Restore cached dependencies
+        uses: actions/cache/restore@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
+        id: cache
+        env:
+          key: ${{ runner.os }}-ghc-${{ steps.setup.outputs.ghc-version }}-cabal-${{ steps.setup.outputs.cabal-version }}
         with:
-          path: |
-            ~\AppData\Roaming\stack
-            ~\AppData\Local\Programs\stack    
-          key: ${{ runner.os }}-ghc-${{ env.GHC_VERSION }}-stack-${{ env.STACK_VERSION }}-stack-global-${{ hashFiles('stack.yaml') }}-${{ hashFiles('package.yaml') }}
-          restore-keys: |
-            ${{ runner.os }}-ghc-${{ env.GHC_VERSION }}-stack-${{ env.STACK_VERSION }}-stack-global-
+          path: ${{ steps.setup.outputs.cabal-store }}
+          key: ${{ env.key }}-plan-${{ hashFiles('**/plan.json') }}
+          restore-keys: ${{ env.key }}-
 
       - name: Build dependencies
-        run: stack build --only-dependencies
+        run: cabal build --only-dependencies
 
-      - name: Build the package
-        run: stack build
-
-      - name: Save .stack-work cache
-        uses: actions/cache/save@v3
-        id: cache-save-stack-work
-        if: steps.cache-restore-stack-work.outputs.cache-hit != 'true'
-        with:
-          path: .stack-work
-          key: ${{ steps.cache-restore-stack-work.outputs.cache-primary-key }}
-   
-      - name: Save %APPDATA%\stack, %LOCALAPPDATA%\Programs\stack cache (Windows)
-        uses: actions/cache/save@v3
-        if: runner.os == 'Windows'
-            && steps.cache-restore-stack-global-windows.outputs.cache-hit != 'true'
+      - name: Save cached dependencies
+        uses: actions/cache/save@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
+        if: steps.cache.outputs.cache-hit != 'true'
         with:
-          path: |
-            ~\AppData\Roaming\stack
-            ~\AppData\Local\Programs\stack    
-          key: ${{ steps.cache-restore-stack-global-windows.outputs.cache-primary-key }}
-  
-      - name: Save ~/.stack cache (Unix)
-        uses: actions/cache/save@v3
-        id: cache-save-stack-global
-        if: (runner.os == 'Linux' || runner.os == 'macOS') 
-            && steps.cache-restore-stack-global-unix.outputs.cache-hit != 'true'
-        with:
-          path: ~/.stack
-          key: ${{ steps.cache-restore-stack-global-unix.outputs.cache-primary-key }}
+          path: ${{ steps.setup.outputs.cabal-store }}
+          key: ${{ steps.cache.outputs.cache-primary-key }}
 
-      - name: Run tests
-        run: stack test
+      - name: Build the package
+        run: cabal build all
 
-      - name: Check cabal file
-        run: cabal check
+      - name: Run tests
+        run: cabal test all
 
       - name: Build documentation
-        run: stack haddock
\ No newline at end of file
+        run: cabal haddock all --disable-documentation
diff --git a/ChangeLog.md b/ChangeLog.md
index 5e6fb45..62325e2 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -2,6 +2,9 @@
 
 ## Unreleased changes
 
+- Use Hspec for tests
+- Add nix flake
+
 ## [v0.2.0.0](https://github.com/rasheedja/LPPaver/tree/v0.2.0.0)
 
 - Setup CI
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..7d8c09d
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,633 @@
+{
+  "nodes": {
+    "HTTP": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1451647621,
+        "narHash": "sha256-oHIyw3x0iKBexEo49YeUDV1k74ZtyYKGR2gNJXXRxts=",
+        "owner": "phadej",
+        "repo": "HTTP",
+        "rev": "9bc0996d412fef1787449d841277ef663ad9a915",
+        "type": "github"
+      },
+      "original": {
+        "owner": "phadej",
+        "repo": "HTTP",
+        "type": "github"
+      }
+    },
+    "cabal-32": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1603716527,
+        "narHash": "sha256-X0TFfdD4KZpwl0Zr6x+PLxUt/VyKQfX7ylXHdmZIL+w=",
+        "owner": "haskell",
+        "repo": "cabal",
+        "rev": "48bf10787e27364730dd37a42b603cee8d6af7ee",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "3.2",
+        "repo": "cabal",
+        "type": "github"
+      }
+    },
+    "cabal-34": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1645834128,
+        "narHash": "sha256-wG3d+dOt14z8+ydz4SL7pwGfe7SiimxcD/LOuPCV6xM=",
+        "owner": "haskell",
+        "repo": "cabal",
+        "rev": "5ff598c67f53f7c4f48e31d722ba37172230c462",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "3.4",
+        "repo": "cabal",
+        "type": "github"
+      }
+    },
+    "cabal-36": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1669081697,
+        "narHash": "sha256-I5or+V7LZvMxfbYgZATU4awzkicBwwok4mVoje+sGmU=",
+        "owner": "haskell",
+        "repo": "cabal",
+        "rev": "8fd619e33d34924a94e691c5fea2c42f0fc7f144",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "3.6",
+        "repo": "cabal",
+        "type": "github"
+      }
+    },
+    "cardano-shell": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1608537748,
+        "narHash": "sha256-PulY1GfiMgKVnBci3ex4ptk2UNYMXqGjJOxcPy2KYT4=",
+        "owner": "input-output-hk",
+        "repo": "cardano-shell",
+        "rev": "9392c75087cb9a3d453998f4230930dea3a95725",
+        "type": "github"
+      },
+      "original": {
+        "owner": "input-output-hk",
+        "repo": "cardano-shell",
+        "type": "github"
+      }
+    },
+    "flake-compat": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1672831974,
+        "narHash": "sha256-z9k3MfslLjWQfnjBtEtJZdq3H7kyi2kQtUThfTgdRk0=",
+        "owner": "input-output-hk",
+        "repo": "flake-compat",
+        "rev": "45f2638735f8cdc40fe302742b79f248d23eb368",
+        "type": "github"
+      },
+      "original": {
+        "owner": "input-output-hk",
+        "ref": "hkm/gitlab-fix",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "hackage": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1758846310,
+        "narHash": "sha256-kVnn9TScof8n41p7LqwvBvoLlfFhLDkjrP+aOAhmQ9k=",
+        "owner": "input-output-hk",
+        "repo": "hackage.nix",
+        "rev": "173aca690d454916a2d1ab5a7d13b593240fa0f5",
+        "type": "github"
+      },
+      "original": {
+        "owner": "input-output-hk",
+        "repo": "hackage.nix",
+        "type": "github"
+      }
+    },
+    "hackage-for-stackage": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1758846300,
+        "narHash": "sha256-uS0e51ny5rGdI5HiOttTYMjGyOqBSoraXDWCY7gFc9g=",
+        "owner": "input-output-hk",
+        "repo": "hackage.nix",
+        "rev": "813f87b29c01a70bf479ff7c72b240d7d6a3fe16",
+        "type": "github"
+      },
+      "original": {
+        "owner": "input-output-hk",
+        "ref": "for-stackage",
+        "repo": "hackage.nix",
+        "type": "github"
+      }
+    },
+    "hackage-internal": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1750307553,
+        "narHash": "sha256-iiafNoeLHwlSLQTyvy8nPe2t6g5AV4PPcpMeH/2/DLs=",
+        "owner": "input-output-hk",
+        "repo": "hackage.nix",
+        "rev": "f7867baa8817fab296528f4a4ec39d1c7c4da4f3",
+        "type": "github"
+      },
+      "original": {
+        "owner": "input-output-hk",
+        "repo": "hackage.nix",
+        "type": "github"
+      }
+    },
+    "haskellNix": {
+      "inputs": {
+        "HTTP": "HTTP",
+        "cabal-32": "cabal-32",
+        "cabal-34": "cabal-34",
+        "cabal-36": "cabal-36",
+        "cardano-shell": "cardano-shell",
+        "flake-compat": "flake-compat",
+        "hackage": "hackage",
+        "hackage-for-stackage": "hackage-for-stackage",
+        "hackage-internal": "hackage-internal",
+        "hls": "hls",
+        "hls-1.10": "hls-1.10",
+        "hls-2.0": "hls-2.0",
+        "hls-2.10": "hls-2.10",
+        "hls-2.11": "hls-2.11",
+        "hls-2.2": "hls-2.2",
+        "hls-2.3": "hls-2.3",
+        "hls-2.4": "hls-2.4",
+        "hls-2.5": "hls-2.5",
+        "hls-2.6": "hls-2.6",
+        "hls-2.7": "hls-2.7",
+        "hls-2.8": "hls-2.8",
+        "hls-2.9": "hls-2.9",
+        "hpc-coveralls": "hpc-coveralls",
+        "iserv-proxy": "iserv-proxy",
+        "nixpkgs": [
+          "haskellNix",
+          "nixpkgs-unstable"
+        ],
+        "nixpkgs-2305": "nixpkgs-2305",
+        "nixpkgs-2311": "nixpkgs-2311",
+        "nixpkgs-2405": "nixpkgs-2405",
+        "nixpkgs-2411": "nixpkgs-2411",
+        "nixpkgs-2505": "nixpkgs-2505",
+        "nixpkgs-unstable": "nixpkgs-unstable",
+        "old-ghc-nix": "old-ghc-nix",
+        "stackage": "stackage"
+      },
+      "locked": {
+        "lastModified": 1758847890,
+        "narHash": "sha256-rGX7RF8Au5ZJJSqlQivsl4seyEslI/K3OnEC9ulLwNM=",
+        "owner": "input-output-hk",
+        "repo": "haskell.nix",
+        "rev": "46abef90b4101ff9253a574cf6fbdc74b78a5863",
+        "type": "github"
+      },
+      "original": {
+        "owner": "input-output-hk",
+        "repo": "haskell.nix",
+        "type": "github"
+      }
+    },
+    "hls": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1741604408,
+        "narHash": "sha256-tuq3+Ip70yu89GswZ7DSINBpwRprnWnl6xDYnS4GOsc=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "682d6894c94087da5e566771f25311c47e145359",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-1.10": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1680000865,
+        "narHash": "sha256-rc7iiUAcrHxwRM/s0ErEsSPxOR3u8t7DvFeWlMycWgo=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "b08691db779f7a35ff322b71e72a12f6e3376fd9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "1.10.0.0",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-2.0": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1687698105,
+        "narHash": "sha256-OHXlgRzs/kuJH8q7Sxh507H+0Rb8b7VOiPAjcY9sM1k=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "783905f211ac63edf982dd1889c671653327e441",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "2.0.0.1",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-2.10": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1743069404,
+        "narHash": "sha256-q4kDFyJDDeoGqfEtrZRx4iqMVEC2MOzCToWsFY+TOzY=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "2318c61db3a01e03700bd4b05665662929b7fe8b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "2.10.0.0",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-2.11": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1747306193,
+        "narHash": "sha256-/MmtpF8+FyQlwfKHqHK05BdsxC9LHV70d/FiMM7pzBM=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "46ef4523ea4949f47f6d2752476239f1c6d806fe",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "2.11.0.0",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-2.2": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1693064058,
+        "narHash": "sha256-8DGIyz5GjuCFmohY6Fa79hHA/p1iIqubfJUTGQElbNk=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "b30f4b6cf5822f3112c35d14a0cba51f3fe23b85",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "2.2.0.0",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-2.3": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1695910642,
+        "narHash": "sha256-tR58doOs3DncFehHwCLczJgntyG/zlsSd7DgDgMPOkI=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "458ccdb55c9ea22cd5d13ec3051aaefb295321be",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "2.3.0.0",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-2.4": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1699862708,
+        "narHash": "sha256-YHXSkdz53zd0fYGIYOgLt6HrA0eaRJi9mXVqDgmvrjk=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "54507ef7e85fa8e9d0eb9a669832a3287ffccd57",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "2.4.0.1",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-2.5": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1701080174,
+        "narHash": "sha256-fyiR9TaHGJIIR0UmcCb73Xv9TJq3ht2ioxQ2mT7kVdc=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "27f8c3d3892e38edaef5bea3870161815c4d014c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "2.5.0.0",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-2.6": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1705325287,
+        "narHash": "sha256-+P87oLdlPyMw8Mgoul7HMWdEvWP/fNlo8jyNtwME8E8=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "6e0b342fa0327e628610f2711f8c3e4eaaa08b1e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "2.6.0.0",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-2.7": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1708965829,
+        "narHash": "sha256-LfJ+TBcBFq/XKoiNI7pc4VoHg4WmuzsFxYJ3Fu+Jf+M=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "50322b0a4aefb27adc5ec42f5055aaa8f8e38001",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "2.7.0.0",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-2.8": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1715153580,
+        "narHash": "sha256-Vi/iUt2pWyUJlo9VrYgTcbRviWE0cFO6rmGi9rmALw0=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "dd1be1beb16700de59e0d6801957290bcf956a0a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "2.8.0.0",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hls-2.9": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1719993701,
+        "narHash": "sha256-wy348++MiMm/xwtI9M3vVpqj2qfGgnDcZIGXw8sF1sA=",
+        "owner": "haskell",
+        "repo": "haskell-language-server",
+        "rev": "90319a7e62ab93ab65a95f8f2bcf537e34dae76a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "haskell",
+        "ref": "2.9.0.1",
+        "repo": "haskell-language-server",
+        "type": "github"
+      }
+    },
+    "hpc-coveralls": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1607498076,
+        "narHash": "sha256-8uqsEtivphgZWYeUo5RDUhp6bO9j2vaaProQxHBltQk=",
+        "owner": "sevanspowell",
+        "repo": "hpc-coveralls",
+        "rev": "14df0f7d229f4cd2e79f8eabb1a740097fdfa430",
+        "type": "github"
+      },
+      "original": {
+        "owner": "sevanspowell",
+        "repo": "hpc-coveralls",
+        "type": "github"
+      }
+    },
+    "iserv-proxy": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1755243078,
+        "narHash": "sha256-GLbl1YaohKdpzZVJFRdcI1O1oE3F3uBer4lFv3Yy0l8=",
+        "owner": "stable-haskell",
+        "repo": "iserv-proxy",
+        "rev": "150605195cb7183a6fb7bed82f23fedf37c6f52a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "stable-haskell",
+        "ref": "iserv-syms",
+        "repo": "iserv-proxy",
+        "type": "github"
+      }
+    },
+    "nixpkgs-2305": {
+      "locked": {
+        "lastModified": 1705033721,
+        "narHash": "sha256-K5eJHmL1/kev6WuqyqqbS1cdNnSidIZ3jeqJ7GbrYnQ=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "a1982c92d8980a0114372973cbdfe0a307f1bdea",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-23.05-darwin",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-2311": {
+      "locked": {
+        "lastModified": 1719957072,
+        "narHash": "sha256-gvFhEf5nszouwLAkT9nWsDzocUTqLWHuL++dvNjMp9I=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "7144d6241f02d171d25fba3edeaf15e0f2592105",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-23.11-darwin",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-2405": {
+      "locked": {
+        "lastModified": 1735564410,
+        "narHash": "sha256-HB/FA0+1gpSs8+/boEavrGJH+Eq08/R2wWNph1sM1Dg=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "1e7a8f391f1a490460760065fa0630b5520f9cf8",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-24.05-darwin",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-2411": {
+      "locked": {
+        "lastModified": 1748037224,
+        "narHash": "sha256-92vihpZr6dwEMV6g98M5kHZIttrWahb9iRPBm1atcPk=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "f09dede81861f3a83f7f06641ead34f02f37597f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-24.11-darwin",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-2505": {
+      "locked": {
+        "lastModified": 1754477006,
+        "narHash": "sha256-suIgZZHXdb4ca9nN4MIcmdjeN+ZWsTwCtYAG4HExqAo=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "4896699973299bffae27d0d9828226983544d9e9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-25.05-darwin",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-unstable": {
+      "locked": {
+        "lastModified": 1754393734,
+        "narHash": "sha256-fbnmAwTQkuXHKBlcL5Nq1sMAzd3GFqCOQgEQw6Hy0Ak=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "a683adc19ff5228af548c6539dbc3440509bfed3",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "old-ghc-nix": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1631092763,
+        "narHash": "sha256-sIKgO+z7tj4lw3u6oBZxqIhDrzSkvpHtv0Kki+lh9Fg=",
+        "owner": "angerman",
+        "repo": "old-ghc-nix",
+        "rev": "af48a7a7353e418119b6dfe3cd1463a657f342b8",
+        "type": "github"
+      },
+      "original": {
+        "owner": "angerman",
+        "ref": "master",
+        "repo": "old-ghc-nix",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "haskellNix": "haskellNix",
+        "nixpkgs": [
+          "haskellNix",
+          "nixpkgs-2505"
+        ]
+      }
+    },
+    "stackage": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1758845522,
+        "narHash": "sha256-SgkvlWF9a+Qrkn791ZOiUVt3wuZXRJ06YjpTZMRy+R8=",
+        "owner": "input-output-hk",
+        "repo": "stackage.nix",
+        "rev": "e2f097d435e38fb6e649efa4a95e214a506a1da5",
+        "type": "github"
+      },
+      "original": {
+        "owner": "input-output-hk",
+        "repo": "stackage.nix",
+        "type": "github"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..69be272
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,45 @@
+{
+  inputs = {
+    haskellNix.url = "github:input-output-hk/haskell.nix";
+    nixpkgs.follows = "haskellNix/nixpkgs-2505";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, haskellNix }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        overlays = [ haskellNix.overlay ];
+        pkgs = import nixpkgs {
+          inherit system overlays;
+          inherit (haskellNix) config;
+        };
+
+        project = pkgs.haskell-nix.cabalProject' {
+          src = ./.;
+          compiler-nix-name = "ghc967";
+          shell = {
+            tools = {
+              cabal = "3.16.0.0";
+              hlint = "3.8";
+              haskell-language-server = "2.11.0.0";
+              fourmolu = "0.17.0.0";
+            };
+            buildInputs = with pkgs; [
+              # system dependencies go here
+            ];
+          };
+        };
+
+        flake = project.flake {};
+      in flake);
+  
+  # --- Flake Local Nix Configuration ---
+  nixConfig = {
+    # This sets the flake to use the IOG nix cache.
+    # Nix should ask for permission before using it,
+    # but remove it here if you do not want it to.
+    extra-substituters = ["https://cache.iog.io"];
+    extra-trusted-public-keys = ["hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ="];
+    allow-import-from-derivation = "true";
+  };
+}
diff --git a/package.yaml b/package.yaml
deleted file mode 100644
index f4ba4bc..0000000
--- a/package.yaml
+++ /dev/null
@@ -1,56 +0,0 @@
-name:                simplex-method
-version:             0.2.0.0
-github:              "rasheedja/simplex-method"
-license:             BSD3
-author:              "Junaid Rasheed"
-maintainer:          "jrasheed178@gmail.com"
-copyright:           "BSD-3"
-
-extra-source-files:
-- README.md
-- ChangeLog.md
-
-# Metadata used when publishing your package
-synopsis:            Implementation of the two-phase simplex method in exact rational arithmetic
-category:            Math, Maths, Mathematics, Optimisation, Optimization, Linear Programming
-
-# To avoid duplicated efforts in documentation and dealing with the
-# complications of embedding Haddock markup inside cabal files, it is
-# common to point users to the README.md file.
-description:         Please see the README on GitHub at <https://github.com/rasheedja/simplex-method#readme>
-
-dependencies:
-- base >= 4.14 && < 5
-- containers >= 0.6.5.1 && < 0.7
-- generic-lens >= 2.2.0 && < 2.3 
-- lens >= 5.2.2 && < 5.3
-- monad-logger >= 0.3.40 && < 0.4
-- text >= 2.0.2 && < 2.1
-- time >= 1.12.2 && < 1.13
-
-default-extensions:
-  DataKinds
-  DeriveFunctor
-  DeriveGeneric
-  DisambiguateRecordFields
-  DuplicateRecordFields
-  FlexibleContexts
-  LambdaCase
-  OverloadedLabels
-  OverloadedRecordDot
-  OverloadedStrings
-  RecordWildCards
-  TemplateHaskell
-  TupleSections
-  TypeApplications
-  NamedFieldPuns
-
-library:
-  source-dirs: src
-
-tests:
-  simplex-haskell-test:
-    main:                Spec.hs
-    source-dirs:         test
-    dependencies:
-    - simplex-method
diff --git a/simplex-method.cabal b/simplex-method.cabal
index 3078198..f3e9673 100644
--- a/simplex-method.cabal
+++ b/simplex-method.cabal
@@ -1,9 +1,3 @@
-cabal-version: 1.12
-
--- This file has been generated from package.yaml by hpack version 0.36.0.
---
--- see: https://github.com/sol/hpack
-
 name:           simplex-method
 version:        0.2.0.0
 synopsis:       Implementation of the two-phase simplex method in exact rational arithmetic
@@ -16,6 +10,7 @@ maintainer:     jrasheed178@gmail.com
 copyright:      BSD-3
 license:        BSD3
 license-file:   LICENSE
+cabal-version:  1.12
 build-type:     Simple
 extra-source-files:
     README.md
@@ -36,34 +31,77 @@ library
   hs-source-dirs:
       src
   default-extensions:
-      DataKinds DeriveFunctor DeriveGeneric DisambiguateRecordFields DuplicateRecordFields FlexibleContexts LambdaCase OverloadedLabels OverloadedRecordDot OverloadedStrings RecordWildCards TemplateHaskell TupleSections TypeApplications NamedFieldPuns
+      DataKinds
+      DeriveFunctor
+      DeriveGeneric
+      DerivingStrategies
+      DisambiguateRecordFields
+      DuplicateRecordFields
+      ExtendedDefaultRules
+      FlexibleContexts
+      GeneralizedNewtypeDeriving
+      LambdaCase
+      NamedFieldPuns
+      OverloadedLabels
+      OverloadedRecordDot
+      OverloadedStrings
+      RecordWildCards
+      TemplateHaskell
+      TupleSections
+      TypeApplications
+      QuasiQuotes
   build-depends:
       base >=4.14 && <5
-    , containers >=0.6.5.1 && <0.7
-    , generic-lens >=2.2.0 && <2.3
-    , lens >=5.2.2 && <5.3
-    , monad-logger >=0.3.40 && <0.4
-    , text >=2.0.2 && <2.1
-    , time >=1.12.2 && <1.13
+    , containers >= 0.6.5.1 && < 0.8
+    , generic-lens >= 2.2 && < 2.3
+    , lens >= 5.2.2 && < 5.4
+    , text >= 2.0.2 && < 2.2
+    , time >= 1.12.2 && < 1.15
+    , monad-logger >= 0.3.40 && < 0.4
+    , QuickCheck >= 2.16.0 && < 2.17
   default-language: Haskell2010
 
 test-suite simplex-haskell-test
   type: exitcode-stdio-1.0
   main-is: Spec.hs
   other-modules:
-      TestFunctions
+      Linear.Simplex.Solver.TwoPhaseSpec
       Paths_simplex_method
   hs-source-dirs:
       test
   default-extensions:
-      DataKinds DeriveFunctor DeriveGeneric DisambiguateRecordFields DuplicateRecordFields FlexibleContexts LambdaCase OverloadedLabels OverloadedRecordDot OverloadedStrings RecordWildCards TemplateHaskell TupleSections TypeApplications NamedFieldPuns
+      DataKinds
+      DeriveFunctor
+      DeriveGeneric
+      DerivingStrategies
+      DisambiguateRecordFields
+      DuplicateRecordFields
+      ExtendedDefaultRules
+      FlexibleContexts
+      GeneralizedNewtypeDeriving
+      LambdaCase
+      NamedFieldPuns
+      OverloadedLabels
+      OverloadedRecordDot
+      OverloadedStrings
+      RecordWildCards
+      TemplateHaskell
+      TupleSections
+      TypeApplications
+      QuasiQuotes
   build-depends:
       base >=4.14 && <5
-    , containers >=0.6.5.1 && <0.7
-    , generic-lens >=2.2.0 && <2.3
-    , lens >=5.2.2 && <5.3
-    , monad-logger >=0.3.40 && <0.4
     , simplex-method
-    , text >=2.0.2 && <2.1
-    , time >=1.12.2 && <1.13
+    , containers >= 0.6.5.1 && < 0.8
+    , generic-lens >= 2.2 && < 2.3
+    , lens >= 5.2.2 && < 5.4
+    , text >= 2.0.2 && < 2.2
+    , time >= 1.12.2 && < 1.15
+    , monad-logger >= 0.3.40 && < 0.4
+    , QuickCheck >= 2.16.0 && < 2.17
+    , hspec >= 2.11.12 && < 2.12
+    , hspec-expectations >= 0.8.3 && < 0.9
+    , interpolatedstring-perl6 >= 1.0.2 && < 1.1
+  build-tool-depends:
+      hspec-discover:hspec-discover >= 2.11.12 && < 2.12
   default-language: Haskell2010
diff --git a/stack.yaml b/stack.yaml
deleted file mode 100644
index eab5650..0000000
--- a/stack.yaml
+++ /dev/null
@@ -1,68 +0,0 @@
-# This file was automatically generated by 'stack init'
-#
-# Some commonly used options have been documented as comments in this file.
-# For advanced use and comprehensive documentation of the format, please see:
-# https://docs.haskellstack.org/en/stable/yaml_configuration/
-
-# Resolver to choose a 'specific' stackage snapshot or a compiler version.
-# A snapshot resolver dictates the compiler version and the set of packages
-# to be used for project dependencies. For example:
-#
-# resolver: lts-3.5
-# resolver: nightly-2015-09-21
-# resolver: ghc-7.10.2
-#
-# The location of a snapshot can be provided as a file or url. Stack assumes
-# a snapshot provided as a file might change, whereas a url resource does not.
-#
-# resolver: ./custom-snapshot.yaml
-# resolver: https://example.com/snapshots/2018-01-01.yaml
-resolver: lts-21.22
-
-# User packages to be built.
-# Various formats can be used as shown in the example below.
-#
-# packages:
-# - some-directory
-# - https://example.com/foo/bar/baz-0.0.2.tar.gz
-#   subdirs:
-#   - auto-update
-#   - wai
-packages:
-- .
-# Dependency packages to be pulled from upstream that are not in the resolver.
-# These entries can reference officially published versions as well as
-# forks / in-progress versions pinned to a git hash. For example:
-#
-# extra-deps:
-# - acme-missiles-0.3
-# - git: https://github.com/commercialhaskell/stack.git
-#   commit: e7b331f14bcffb8367cd58fbfc8b40ec7642100a
-#
-# extra-deps: {}
-
-# Override default flag values for local packages and extra-deps
-# flags: {}
-
-# Extra package databases containing global packages
-# extra-package-dbs: []
-
-# Control whether we use the GHC we find on the path
-# system-ghc: true
-#
-# Require a specific version of stack, using version ranges
-# require-stack-version: -any # Default
-# require-stack-version: ">=2.5"
-#
-# Override the architecture used by stack, especially useful on Windows
-# arch: i386
-# arch: x86_64
-#
-# Extra directories used by stack for building
-# extra-include-dirs: [/path/to/dir]
-# extra-lib-dirs: [/path/to/dir]
-#
-# Allow a newer minor version of GHC than the snapshot specifies
-# compiler-check: newer-minor
-
-system-ghc: true
diff --git a/stack.yaml.lock b/stack.yaml.lock
deleted file mode 100644
index e8d3cc7..0000000
--- a/stack.yaml.lock
+++ /dev/null
@@ -1,12 +0,0 @@
-# This file was autogenerated by Stack.
-# You should not edit this file by hand.
-# For more information, please see the documentation at:
-#   https://docs.haskellstack.org/en/stable/lock_files
-
-packages: []
-snapshots:
-- completed:
-    sha256: afd5ba64ab602cabc2d3942d3d7e7dd6311bc626dcb415b901eaf576cb62f0ea
-    size: 640060
-    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/21/22.yaml
-  original: lts-21.22
diff --git a/test/TestFunctions.hs b/test/Linear/Simplex/Solver/TwoPhaseSpec.hs
similarity index 95%
rename from test/TestFunctions.hs
rename to test/Linear/Simplex/Solver/TwoPhaseSpec.hs
index b2af317..06b98d9 100644
--- a/test/TestFunctions.hs
+++ b/test/Linear/Simplex/Solver/TwoPhaseSpec.hs
@@ -1,9 +1,21 @@
-module TestFunctions where
+module Linear.Simplex.Solver.TwoPhaseSpec where
 
+import Prelude hiding (EQ)
+
+import Control.Monad
+import Control.Monad.IO.Class
+import Control.Monad.Logger
 import qualified Data.Map as M
 import Data.Ratio
+import Text.InterpolatedString.Perl6
+
+import Test.Hspec
+import Test.Hspec.Expectations.Contrib (annotate)
+
+import Linear.Simplex.Prettify
+import Linear.Simplex.Solver.TwoPhase
 import Linear.Simplex.Types
-import Prelude hiding (EQ)
+import Linear.Simplex.Util
 
 testsList :: [((ObjectiveFunction, [PolyConstraint]), Maybe Result)]
 testsList =
@@ -1046,3 +1058,35 @@ testQuickCheck3 =
     , GEQ (M.fromList [(1, -5), (2, -1), (2, 1)]) (-5)
     ]
   )
+
+spec :: Spec
+spec = describe "twoPhaseSimplex" $ do
+  it "Check golden tests" $ do
+    forM_ testsList $
+      \((obj, constraints), expectedResult) -> do
+        actualResult <-
+          runStdoutLoggingT $
+            filterLogger (\_logSource logLevel -> logLevel > LevelInfo) $
+              twoPhaseSimplex obj constraints
+        let prettyObj = prettyShowObjectiveFunction obj
+            prettyConstraints = map prettyShowPolyConstraint constraints
+
+            expectedObjVal = extractObjectiveValue expectedResult
+            actualObjVal = extractObjectiveValue actualResult
+        annotate
+          [qc|
+             
+Objective Function (Non-prettified): {obj}
+Constraints        (Non-prettified): {constraints}
+====================================
+Objective Function     (Prettified): {prettyObj}
+Constraints            (Prettified): {prettyConstraints}
+====================================
+Expected Solution            (Full): {expectedResult}
+Actual Solution              (Full): {actualResult}
+Expected Solution       (Objective): {expectedObjVal}
+Actual Solution         (Objective): {actualObjVal}
+
+          |]
+          $ do
+            actualResult `shouldBe` expectedResult
diff --git a/test/Spec.hs b/test/Spec.hs
index 4a8ad55..a824f8c 100644
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -1,42 +1 @@
-module Main where
-
-import Control.Monad
-import Control.Monad.IO.Class
-import Control.Monad.Logger
-
-import Linear.Simplex.Prettify
-import Linear.Simplex.Solver.TwoPhase
-import Linear.Simplex.Types
-import Linear.Simplex.Util
-
-import TestFunctions
-
-main :: IO ()
-main = runStdoutLoggingT $ filterLogger (\_logSource logLevel -> logLevel > LevelInfo) $ runTests testsList
-
-runTests :: (MonadLogger m, MonadFail m, MonadIO m) => [((ObjectiveFunction, [PolyConstraint]), Maybe Result)] -> m ()
-runTests [] = do
-  liftIO $ putStrLn "All tests passed"
-  pure ()
-runTests (((testObjective, testConstraints), expectedResult) : tests) =
-  do
-    testResult <- twoPhaseSimplex testObjective testConstraints
-    if testResult == expectedResult
-      then runTests tests
-      else do
-        let msg =
-              "\nThe following test failed: "
-                <> ("\nObjective Function (Non-prettified): " ++ show testObjective)
-                <> ("\nConstraints        (Non-prettified): " ++ show testConstraints)
-                <> "\n===================================="
-                <> ("\nObjective Function (Prettified): " ++ prettyShowObjectiveFunction testObjective)
-                <> "\nConstraints        (Prettified): "
-                <> "\n"
-                <> concatMap (\c -> "\t" ++ prettyShowPolyConstraint c ++ "\n") testConstraints
-                <> "\n===================================="
-                <> ("\nExpected Solution      (Full): " ++ show expectedResult)
-                <> ("\nActual Solution        (Full): " ++ show testResult)
-                <> ("\nExpected Solution (Objective): " ++ show (extractObjectiveValue expectedResult))
-                <> ("\nActual Solution   (Objective): " ++ show (extractObjectiveValue testResult))
-                <> "\n"
-        fail msg
+{-# OPTIONS_GHC -F -pgmF hspec-discover #-}