add Fault monad

nib/std/fault.nix

@@ -0,0 +1,16 @@
+{...}: rec {
+  # Fault Monad
+  # Wrapper around an error (ie builtins.abort)
+  Fault = error: {
+    error = error;
+  };
+
+  # Pattern Matching
+  isFault = F: builtins.attrNames F == ["error"];
+
+  # Unwrap (Monadic Return Operation)
+  unwrap = F: F.error;
+
+  # Map (Monadic Bind Operation)
+  map = f: F: Fault (f (unwrap F));
+}