add shell for preparing dev tooling and generate purs-packages.nix

pinned.nix

+import (
+  builtins.fetchTarball {
+    url = "https://github.com/nixos/nixpkgs/archive/ece829033b7b8f4e81261fef5427144df4147bc4.tar.gz";
+    sha256 = "07n91k3d9i9pym8npsszha9mnvg4d1r0l0ldnhk4g8sx15vv1br5";
+  }
+)

shell.nix

+{ pkgs ? import ./pinned.nix {} }:
+let
+  easy-ps = import (
+    pkgs.fetchFromGitHub {
+      owner = "justinwoo";
+      repo = "easy-purescript-nix";
+      rev = "14e7d85431e9f9838d7107d18cb79c7fa534f54e";
+      sha256 = "0lmkppidmhnayv0919990ifdd61f9d23dzjzr8amz7hjgc74yxs0";
+    }
+  ) {
+    inherit pkgs;
+  };
+
+  soba = import (
+    pkgs.fetchFromGitHub {
+      owner = "justinwoo";
+      repo = "soba";
+      rev = "2add8804bce7e7c1ab5eb1c3d8f6783e938a04d3";
+      sha256 = "1qagyklcllr2sxdb315prw33af6g37762zgk2ahh3ifxpns6ifxx";
+    }
+  ) {
+    inherit pkgs;
+  };
+
+  purs-packages = import ./purs-packages.nix { inherit pkgs; };
+
+  cpPackage = pp:
+    let
+      target = ".psc-package/local/${pp.name}/${pp.version}";
+    in
+      ''
+        mkdir -p ${target}
+        cp --no-preserve=mode,ownership,timestamp -r ${pp.fetched.outPath}/* ${target}
+      '';
+
+  install-purs-packages = pkgs.writeShellScriptBin "install-purs-packages" ''
+    #!/usr/bin/env bash
+    ${builtins.toString (builtins.map cpPackage (builtins.attrValues purs-packages))}
+    echo done installing deps.
+  '';
+
+  build-purs = pkgs.writeShellScriptBin "build-purs" ''
+    #!/usr/bin/env bash
+    purs compile "src/**/*.purs" ".psc-package/*/*/*/src/**/*.purs"
+  '';
+
+  storePath = x: ''"${x.fetched.outPath}/src/**/*.purs"'';
+
+  build-purs-from-store = pkgs.writeShellScriptBin "build-purs-from-store" ''
+    #!/usr/bin/env bash
+    purs compile "src/**/*.purs" \
+      ${builtins.toString (builtins.map storePath (builtins.attrValues purs-packages))}
+  '';
+in
+pkgs.mkShell {
+  buildInputs = [
+    easy-ps.purs
+    easy-ps.psc-package
+    soba
+    install-purs-packages
+    build-purs
+    build-purs-from-store
+    pkgs.yarn
+  ];
+}
+
+## how to build the project with nix dependencies:
+#
+# 1. start a nix shell (e.g. `nix-shell -j 20`, this uses 20 jobs to fetch deps)
+# 2. run `yarn` to install npm deps
+# 3. run `install-purs-packages` if you want dependencies locally, available for psc-package and for inspection
+# 4. run `build-purs` to build from local sources. otherwise use `build-purs-from-store`.
+#
+# note that the purescript compiler uses filepaths and timestamps, so using the above two commands
+# interchangeably will lead to constant rebuilding of the entire project.
+#
+## how to update purs-packages.nix
+#
+# 1. run `soba insdhall` to generate packages.json
+# 2. run `soba nix` to generate a nix derivation from packages.json
+