build: adding nix, shell, and haskell code formatters

These need to be run through the top-level nix-shell/shell.nix

sh/fmt

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+
+# Usage: fmt
+
+# Run all formatters and linters ensuring codebase consistency
+
+set -euo pipefail
+
+cd "${0%/*}"
+
+./fmt-shell
+./fmt-nix
+./fmt-haskell
+
+echo 'Done.'

sh/fmt-haskell

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+# Usage: fmt-haskell
+
+set -euo pipefail
+
+cd "${0%/*}/.."
+
+echo "Formatting Haskell"
+
+# FIXME: Avoid inplace (-i) modifications for now.
+find pkg/hs -type f -name '*.hs' \
+    -exec ormolu --mode check \
+    -o '-XBangPatterns' \
+    -o '-XMagicHash' \
+    -o '-XTypeApplications' \
+    -o '-XPatternSynonyms' \
+    {} \+

sh/fmt-nix

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+# Usage: fmt-nix
+
+set -euo pipefail
+
+cd "${0%/*}/.."
+
+echo "Formatting Nix"
+
+find . -type f -name '*.nix' \
+    -exec nixfmt {} \+

sh/fmt-shell

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+# Usage: fmt-shell
+
+set -euo pipefail
+
+cd "${0%/*}/.."
+
+echo "Formatting Shell"
+
+# FIXME: Avoid inplace (-w) modifications for now.
+find sh -type f \
+    -exec shfmt -s -i 2 -ln bash -l {} \+ \
+    -exec shellcheck --shell=bash --format=tty {} \+