define a monadic result attribute set

nib/std/result.nix

@@ -0,0 +1,46 @@
+{lists}: rec {
+  # Result Monad
+  Ok = value: {
+    ok = true;
+    value = value;
+  };
+  Err = err: {
+    ok = false;
+    error = err;
+  };
+
+  # Pattern Matching
+  isOk = r: builtins.hasAttr "ok" r && r.ok;
+  isErr = r: builtins.hasAttr "ok" r && !r.ok;
+
+  # Unwrap (Monadic Return Operation)
+  unwrap = f: r:
+    if isOk r
+    then r.value
+    else f r.error;
+
+  unwrapDefault = default: unwrap (x: default);
+
+  # Map (Monadic Bind Operation)
+  identity = r: r;
+
+  map = r: f: g:
+    if isOk r
+    then Ok (f r.value)
+    else Err (g r.value);
+  mapOk = f: map f identity;
+  mapErr = f: map identity f;
+
+  # Conditionals
+  okOr = r: f:
+    if isOk r
+    then r
+    else f r;
+
+  errOr = r: f:
+    if isErr r
+    then r
+    else f r;
+
+  firstErr = lists.findFirst isErr (Ok "No errors");
+}