fix: error when inner value is undefined

src/match.ts

@@ -14,12 +14,12 @@ interface Match<Tag extends string> {
 }
 
 const tryMatch = (tag: string, [k, field, ...rest]: string[], v: any): unknown => {
+  if (!k) return [v]
+  if (k === '_') return [null]
+  if (v?.[tag] !== k) return
   if (!v) return
-  if (!k) return v
-  if (k === '_') return null
-  if (v[tag] !== k) return
   if (field) return tryMatch(tag, rest, v[field])
-  return v
+  return [v]
 }
 
 export const matchFor = <Tag extends string>(tag: Tag): Match<Tag> =>
@@ -28,8 +28,8 @@ export const matchFor = <Tag extends string>(tag: Tag): Match<Tag> =>
       for (const [p, f] of Object.entries(pattern)) {
         const ps = p === '_' ? ['_'] : p.split('_')
         const m = tryMatch(tag, ps, value)
-        if (m !== undefined) {
-          return f(m ?? undefined)
+        if (m !== undefined && Array.isArray(m)) {
+          return f(m[0] ?? undefined)
         }
       }
       throw new TypeError('Incomplete pattern!')

test/matchWithSingle.ts

@@ -4,6 +4,17 @@ import { none, Option, some } from './types/utils'
 
 const match = matchWithFor('_tag')
 
+test('option undefined', t => {
+  const o = some(void 0)
+  t.is(
+    match(o).with({
+      Some_value: () => 1,
+      None: () => 0,
+    }),
+    1,
+  )
+})
+
 test('option some', t => {
   const o = some('TS')