1 files changed, 26 insertions, 0 deletions
diff --git a/src/utils/adt.ts b/src/utils/adt.ts
new file mode 100644
index 0000000..c19398b
--- /dev/null
+++ b/src/utils/adt.ts
@@ -0,0 +1,26 @@
+type TagValue<T, N> = T extends Tag<N, infer V> ? V : never
+
+export const match =
+  <R, T extends Tag<string, any>>(pattern: {
+    [key in T['tag'] | '_']?: (v: TagValue<T, key>) => R
+  }) =>
+  (tag: T): R =>
+    ((pattern as any)[tag.tag] || (pattern._ as any))(tag.value)
+
+type Tag<N, V> = { tag: N; value: V }
+export type Enum<T> = { [N in keyof T]: Tag<N, T[N]> }[keyof T]
+
+export const constructors = <T extends Tag<string, any>>(): {
+  [N in T['tag']]: TagValue<T, N> extends null | never
+    ? (value?: null | never) => T
+    : (value: TagValue<T, N>) => T
+} =>
+  new Proxy(
+    {},
+    {
+      get(_, k) {
+        return (value: any) => ({ tag: k, value })
+      },
+    },
+  ) as any
+