From e243ee065668cdd856349972a1ee83a291da67db Mon Sep 17 00:00:00 2001
From: AlexKnauth <alexander@knauth.org>
Date: Tue, 3 May 2016 11:00:41 -0400
Subject: [PATCH] =?UTF-8?q?add=20=3F=E2=88=80=20and=20=3F=CE=9B?=
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---
 tapl/mlish.rkt | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/tapl/mlish.rkt b/tapl/mlish.rkt
index 8056881..1608bde 100644
--- a/tapl/mlish.rkt
+++ b/tapl/mlish.rkt
@@ -31,6 +31,25 @@
 ;; - pattern matching
 ;; - (local) type inference
 
+;; creating possibly polymorphic types
+;; ?∀ only wraps a type in a forall if there's at least one type variable
+(define-syntax ?∀
+  (lambda (stx)
+    (syntax-case stx ()
+      [(?∀ () body)
+       #'body]
+      [(?∀ (X ...) body)
+       #'(∀ (X ...) body)])))
+
+;; ?Λ only wraps an expression in a Λ if there's at least one type variable
+(define-syntax ?Λ
+  (lambda (stx)
+    (syntax-case stx ()
+      [(?Λ () body)
+       #'body]
+      [(?Λ (X ...) body)
+       #'(Λ (X ...) body)])))
+
 (begin-for-syntax 
   ;; matching possibly polymorphic types
   (define-syntax ~?∀