fix bug in dict comparison

tests/dict.js

@@ -0,0 +1,29 @@
+import assert from "node:assert";
+
+import { compareInts, compareStrings } from "../lib/compare/primitives.js";
+import { compareDicts } from "../lib/compare/structures.js";
+import { emptyDict, set } from "../lib/structures/dict.js";
+
+const cmpFn = compareDicts(compareStrings)(compareInts);
+
+const e = emptyDict(compareStrings);
+const f = set(e)("x")(1n);
+const g = set(f)("y")(2n);
+
+assert.equal(
+  cmpFn(e)(e),
+  0,
+  "empty dict should be equal to itself"
+);
+
+assert.equal(
+  cmpFn(g)(g),
+  0,
+  "dict should always equal itself"
+);
+
+assert.equal(
+  cmpFn(f)(g),
+  -1,
+  "f is smaller"
+);