make t.recursion slightly more type safe

src/index.ts

@@ -351,11 +351,16 @@ export class RecursiveType<RT extends Any, A = any, O = A, I = mixed> extends Ty
  }
 }
 
-export const recursion = <A, RT extends Mixed = Mixed, O = A, I = mixed>(
+export const recursion = <A, O = mixed, I = mixed, RT extends Type<A, O, I> = Type<A, O, I>>(
  name: string,
  definition: (self: RT) => RT
 ): RecursiveType<RT, A, O, I> => {
- const Self: any = new RecursiveType(name, (m): m is A => type.is(m), (m, c) => type.validate(m, c), identity)
+ const Self: any = new RecursiveType<RT, A, O, I>(
+ name,
+ (m): m is A => type.is(m),
+ (m, c) => type.validate(m, c),
+ identity as any
+ )
  const type = definition(Self)
  Self.type = type
  Self.serialize = type.serialize

typings-checker/index.ts

@@ -270,11 +270,11 @@ type Rec = {
  b: Rec | undefined
 }
 
-const Rec = t.recursion<Rec, Generable>('T', self =>
- t.interface({
+const RecRT = t.recursion<Rec, Rec, t.mixed, GenerableInterface>('T', self => {
+ return t.interface({
  a: t.number,
  b: t.union([self, t.undefined])
  })
-)
+})
 
-f(Rec) // OK!
+f(RecRT) // OK!