fix expected-ty propagation in cond else; closes #3

tapl/mlish.rkt

@@ -482,7 +482,7 @@
    #:when (same-types? #'(ty_body ...))
    #:with τ_out (stx-car #'(ty_body ...))
    #:with [last-body- last-ty] (if (attribute else_body)
-                                   (infer+erase #'else_body)
+                                   (infer+erase #'(add-expected else_body ty-expected))
                                    (infer+erase #'(void)))
    #:with ([last-b- last-b-ty] ...) (if (attribute else_body)
                                    (infers+erase #'(else_b ...))

tapl/tests/mlish/inst.mlish

@@ -32,3 +32,7 @@
   (h))
 
 (check-type i : (→/test (Result Int String)))
+
+(define (f/cond [b : Bool] -> (Result Int String))
+  (cond [b (ok 1)]
+        [else (ok 0)]))