Change order of type<: in pat⇐

Added Laarhoven lenses type as a test.

closes #46

Author: iitalics

hackett-lib/hackett/private/adt.rkt

@@ -327,7 +327,7 @@
         (values (listof (cons/c identifier? type?))
                 (-> (listof identifier?) (values syntax? (listof identifier?)))))
     (let-values ([(t_⇒ assumps mk-pat) (pat⇒! pat)])
-      (type<:! t_⇒ t #:src (pat-base-stx pat))
+      (type<:! t t_⇒ #:src (pat-base-stx pat))
       (values assumps mk-pat)))
 
   ; Combines a list of `match` pattern constructors to properly run them against a list of identifiers

hackett-test/tests/hackett/integration/laar-lens.rkt

@@ -0,0 +1,14 @@
+#lang hackett
+(require hackett/data/identity)
+
+(data (Lens s t a b)
+  (L (∀ [f] (Functor f) => {{a -> (f b)} -> {s -> (f t)}})))
+
+(defn make-lens : (∀ [s t a b] {{s -> a} -> {s -> b -> t} -> (Lens s t a b)})
+  [[get set]
+   (L (λ [afb s]
+        {(set s) <$> (afb (get s))}))])
+
+(defn modify : (∀ [s t a b] {(Lens s t a b) -> {a -> b} -> {s -> t}})
+  [[(L l) func s]
+   (run-identity (l {Identity . func} s))])

hackett-test/tests/hackett/regression/github-issue-46.rkt

@@ -0,0 +1,6 @@
+#lang hackett
+
+(data Nop
+  (nop (∀ [a] {a -> a})))
+(defn ->nop : (∀ [a] {a -> Nop -> a})
+  [[x (nop f)] (f x)])