add postfix-in require form

tapl/postfix-in.rkt

@@ -0,0 +1,36 @@
+#lang racket/base
+
+(provide postfix-in)
+
+(require racket/require-syntax
+         racket/require
+         (for-syntax racket/base
+                     syntax/parse
+                     ))
+(module+ test
+  (require rackunit))
+
+(begin-for-syntax
+  ;; add-postfix : (-> String (-> String String))
+  (define ((add-postfix postfix) str)
+    (string-append str postfix)))
+
+(define-require-syntax postfix-in
+  (lambda (stx)
+    (syntax-parse stx
+      [(postfix-in post-id:id require-spec)
+       #:with post-str:str (symbol->string (syntax-e #'post-id))
+       #'(filtered-in (add-postfix 'post-str) require-spec)])))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(module+ test
+  (require (postfix-in - racket/base))
+
+  (define-binary-check (check-free-id=? actual expected)
+    (free-identifier=? actual expected))
+  
+  (check-free-id=? #'#%app- #'#%app)
+  (check-free-id=? #'λ- #'λ)
+  (check-free-id=? #'define- #'define)
+  )