Add a rule for single-case case-lambda (#260)

default-recommendations/function-shortcuts-test.rkt

@@ -31,3 +31,8 @@ test: "apply with recursive list* can be flattened"
 test: "apply with quasiquoted list can be flattened"
 - (apply + 0 `(1 2 ,@'(3 4)))
 - (apply + 0 1 2 '(3 4))
+
+
+test: "single-case case-lambda refactorable to regular lambda"
+- (case-lambda [(x y z) (+ x y z)])
+- (λ (x y z) (+ x y z))

default-recommendations/function-shortcuts.rkt

@@ -65,8 +65,15 @@
    (id function arg ... trailing-arg.lifted ... trailing-arg.trailing)])
 
 
+(define-refactoring-rule case-lambda-with-single-case-to-lambda
+  #:description "This `case-lambda` form only has one case. Use a regular lambda instead."
+  #:literals (case-lambda)
+  [(case-lambda [args body ...]) (λ args body ...)])
+
+
 (define function-shortcuts
   (refactoring-suite
    #:name (name function-shortcuts)
    #:rules
-   (list apply-flattening)))
+   (list apply-flattening
+         case-lambda-with-single-case-to-lambda)))