[XMonad] Use nix for xmonad build script

dotfiles/config/xmonad/build

@@ -1,32 +1,11 @@
 #!/usr/bin/env bash
 
-function min {
-	[ $1 -le $2 ] && echo "$1" || echo "$2"
-}
-
-function get_exe_dir {
-	# XXX: This exists because calling in to stack is kind of slow with nix
-	# integration enabled, even when just using it to get a path.
-	if [ -e ./.cached-stack-install-path ]; then
-		cat .cached-stack-install-path
-	else
-		stack path --local-install-root
-	fi
-}
-
 SRC_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 
-EXE_NAME=imalison-xmonad
-EXE_LOCATION=$(get_exe_dir)/bin/$EXE_NAME
 output_file=$1; shift
 
-if [ -e ./.cached-stack-install-path ]; then
-	last_built=$(stat -c '%Y' $EXE_LOCATION)
-	xmonad_modified=$(stat -c '%Y' ./xmonad.hs)
-
-	[ $last_built -lt $xmonad_modified ] && stack install
-else
-	stack install
-fi
-
-cp -uf $EXE_LOCATION $output_file
+cd "$SRC_DIR"
+exe_location="$SRC_DIR/result/bin/imalison-xmonad"
+nix-build
+echo "$exe_location" "$output_file" > did_build
+cp -f "$exe_location" "$output_file"