Build all the way to android:
nix-build -A androidApp
Build only the haskell bit:
nix-build -A hsApp
Get a shell with cross binutils:
nix-shell -E 'let rp = (import ./reflex-platform {}).nixpkgsCross.android.arm64; in rp.stdenv.mkDerivation { name = "shell"; buildInput = [ rp.buildPackages.binutilsCross ]; }'
Get a shell with cross ghc:
nix-shell -E 'let rp = (import ./reflex-platform {}).ghcAndroidArm64; in rp.stdenv.mkDerivation { name = "shell"; buildInput = [ rp.ghc ]; }'