test sub1 on Int>1 returns PosInt

Author: AlexKnauth

typed-racket-test/succeed/sub1-int-gt-1.rkt

@@ -0,0 +1,13 @@
+#lang typed/racket
+
+;; From this stack overflow question by Lyu Yao Ting:
+;; Type mismatch issue of sub1
+;; https://stackoverflow.com/questions/58887937/type-mismatch-issue-of-sub1
+
+(define-predicate one? One)
+(: pick1 (-> Positive-Integer (Listof Any) Any))
+(define pick1
+  (λ (n lat)
+    (cond [(one? n) (car lat)]
+          [else (pick1 (sub1 n)
+                       (cdr lat))])))