chore: add nix

Author: RyosukeDTomita

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -1,2 +1,29 @@
 # all .out files
 *.out
+input.txt
+inputs.txt
+.direnv/
+# https://github.com/github/gitignore/blob/main/Haskell.gitignore
+dist
+dist-*
+cabal-dev
+*.o
+*.hi
+*.hie
+*.chi
+*.chs.h
+*.dyn_o
+*.dyn_hi
+.hpc
+.hsenv
+.cabal-sandbox/
+cabal.sandbox.config
+*.prof
+*.aux
+*.hp
+*.eventlog
+.stack-work/
+cabal.project.local
+cabal.project.local~
+.HTF/
+.ghc.environment.*

flake.lock

@@ -0,0 +1,37 @@
+{
+  description = "Haskell dev environment AtCoder";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+      in
+      {
+        formatter = nixpkgs.legacyPackages.${system}.nixfmt-tree;
+
+        devShells.default = pkgs.mkShell {
+          packages = [
+            pkgs.zsh
+            (pkgs.haskell.packages.ghc96.ghcWithPackages (ps: [
+              ps.vector
+              ps.containers
+              ps.bytestring
+            ]))
+            pkgs.haskell.packages.ghc96.cabal-install
+            pkgs.haskell.packages.ghc96.haskell-language-server
+          ];
+        };
+      }
+    );
+}