Update shell.nix files to ghc843. Try pinning stack.yaml to a 18.09 n…

…ixpkgs tarball.

gibbon-compiler/shell.nix

@@ -9,7 +9,7 @@
 # whatever nixpkgs your user account is currently pointing at.
 { pkgs ? import (fetchTarball (import ../.nix_default_environment.txt)) {}
  # Default should match the current LTS in stack.yaml:
-, ghc ? pkgs.haskell.compiler.ghc822 }:
+, ghc ? pkgs.haskell.compiler.ghc843 }:
 
 with pkgs;
 

gibbon-compiler/stack.yaml

@@ -19,8 +19,9 @@ nix:
   packages: [gcc, which]
   # path: ["https://github.com/NixOS/nixpkgs-channels/archive/nixos-17.03.tar.gz"]
   # nixos-unstable snapshot:
-  # path: ["nixpgs=https://github.com/NixOS/nixpkgs-channels/archive/1e1472ed93e1256dfdac4908ae8edcb90ceff21c.tar.gz"]
+  # path: ["nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/1e1472ed93e1256dfdac4908ae8edcb90ceff21c.tar.gz"]
   # shell-file: shell.nix
+  path: ["nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.09.tar.gz"]
 
 # [2018.05.23] (chai):
 # Ugh, Stack fails to construct a build plan with my system GHC, even though it's pinned to 8.2.2,

shell.nix

@@ -4,7 +4,7 @@
 # Currently using a snapshot of the nixos-18.03 channel.
 # Default GHC should match the current LTS in stack.yaml:
 { pkgs ? import (fetchTarball (import ./.nix_default_environment.txt)) {}
-, ghc ? pkgs.haskell.compiler.ghc822 }:
+, ghc ? pkgs.haskell.compiler.ghc843 }:
 
 with pkgs;