feat: improve inference of return types

.changeset/thin-dancers-reply.md

@@ -0,0 +1,22 @@
+---
+'exhaustive': patch
+---
+
+Improve inference of return types with new generic value
+
+The return type of `exhaustive` and `exhaustive.tag` will now be inferred based on the return type of the callback function.
+
+```ts
+type Union = 'IDLE' | 'LOADING' | 'SUCCESS' | 'ERROR';
+
+type HumanReadableUnion = 'idle' | 'loading' | 'success' | 'error';
+
+function unionToHumanReadableString(union: Union): HumanReadableUnion {
+  return exhaustive(union, {
+    IDLE: () => 'idle',
+    LOADING: () => 'loading',
+    SUCCESS: () => 'success',
+    ERROR: (value) => value.toLowerCase(), // type `string` is not assignable to type `HumanReadableUnion`
+  });
+}
+```