Add Dhall env

dhall/.envrc

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+use flake .

dhall/flake.lock

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+{
+  "nodes": {
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1656928814,
+        "narHash": "sha256-RIFfgBuKz6Hp89yRr7+NR5tzIAbn52h8vT6vXkYjZoM=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "7e2a3b3dfd9af950a856d66b0a7d01e3c18aa249",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1659047146,
+        "narHash": "sha256-2qZemVRDR5oCw0Hd32LQSWC7FaEy5sUp5ih9OxqE3yU=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "68716026a095a765c09ec29f06ba234a0298418c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

dhall/flake.nix

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+{
+  description = "A Nix-flake-based Dhall development environment";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+        dhall = pkgs.dhall;
+
+        inherit (pkgs.lib) optionals;
+        inherit (pkgs.stdenv) isLinux;
+
+        otherFormats = with pkgs.haskellPackages; [
+          dhall-bash
+          dhall-docs
+          dhall-lsp-server
+          dhall-nix
+          dhall-json
+          dhall-toml
+          dhall-yaml
+        ] ++ optionals isLinux (with pkgs.haskellPackages; [ dhall-csv dhall-haskell ]);
+
+        inherit (pkgs) mkShell;
+      in {
+        devShells = {
+          default = pkgs.mkShell {
+            buildInputs = [ dhall ] ++ otherFormats;
+
+            shellHook = ''
+              echo "dhall `${dhall}/bin/dhall --version`"
+            '';
+          };
+        };
+      });
+}