Split shell.nix files per language

This allows to only download and build environment for the actual
language one is playing with.
Also do not use downloaded binary but provide a derivation for exercism
binary.

c/shell.nix

@@ -0,0 +1,11 @@
+{
+  pkgs ? import <nixpkgs> { }
+}:
+
+pkgs.mkShellNoCC {
+  name = "exercism";
+  buildInputs = [
+    pkgs.coreutils
+    (pkgs.callPackage ../exercism.nix { })
+  ];
+}

exercism.nix

@@ -0,0 +1,25 @@
+{
+  buildGoModule
+  , fetchFromGitHub
+  , lib
+}:
+
+buildGoModule rec {
+  pname = "exercism";
+  version = "3.3.0";
+  src = fetchFromGitHub {
+    owner = "exercism";
+    repo = "cli";
+    rev = "v${version}";
+    sha256 = "Mtb5c1/k8kp7bETOSE0X969BV176jpoprr1/mQ3E4Vg=";
+  };
+
+  vendorHash = "sha256-fnsSvbuVGRAndU88su2Ck7mV8QBDhxozdmwI3XGtxcA=";
+
+  meta = with lib; {
+    homepage = "https://github.com/exercism/cli";
+    description = "Command line interface for exercism website";
+    license = licenses.mit;
+    platforms = platforms.linux;
+  };
+}

go/shell.nix

@@ -0,0 +1,11 @@
+{
+  pkgs ? import <nixpkgs> { }
+}:
+
+pkgs.mkShellNoCC {
+  name = "exercism";
+  buildInputs = [
+    pkgs.go
+    (pkgs.callPackage ../exercism.nix { })
+  ];
+}

lua/shell.nix

@@ -0,0 +1,11 @@
+{
+  pkgs ? import <nixpkgs> { }
+}:
+
+pkgs.mkShellNoCC {
+  name = "exercism";
+  buildInputs = [
+    (pkgs.lua.withPackages(ps: with ps; [ busted]))
+    (pkgs.callPackage ../exercism.nix { })
+  ];
+}

python/shell.nix

@@ -0,0 +1,11 @@
+{
+  pkgs ? import <nixpkgs> { }
+}:
+
+pkgs.mkShellNoCC {
+  name = "exercism";
+  buildInputs = [
+    (pkgs.python311.withPackages(ps: with ps; [ pytest ]))
+    (pkgs.callPackage ../exercism.nix { })
+  ];
+}

rust/shell.nix

@@ -0,0 +1,14 @@
+{
+  pkgs ? import <nixpkgs> { }
+}:
+
+pkgs.mkShellNoCC {
+  name = "exercism";
+  buildInputs = [
+    pkgs.gcc
+    pkgs.rustc
+    pkgs.cargo
+
+    (pkgs.callPackage ../exercism.nix { })
+  ];
+}

shell.nix

@@ -1,28 +0,0 @@
-{
-  pkgs ? import <nixpkgs> { }
-}:
-
-pkgs.mkShellNoCC {
-  name = "exercism";
-  buildInputs = [
-    # coreutils provides "make" for c compiling
-    pkgs.coreutils
-
-    (pkgs.lua.withPackages(ps: with ps; [ busted]))
-
-    (pkgs.python311.withPackages(ps: with ps; [ pytest ]))
-
-    pkgs.go
-
-    # Rust (needs gcc compiler)
-    pkgs.gcc
-    pkgs.rustc
-    pkgs.cargo
-
-  ];
-
-  shellHook = ''
-    # Expose exercism binary to PATH, see: https://exercism.org/cli-walkthrough
-    export PATH="$(pwd):$PATH"
-  '';
-}