From b050c4f1922ea9789ebf99adc70a9b06b8c9dc80 Mon Sep 17 00:00:00 2001
From: "William J. Bowman" <wjb@williamjbowman.com>
Date: Sat, 3 Oct 2015 04:09:16 -0400
Subject: [PATCH] Better error messages for let, in certain cases

---
 stdlib/sugar.rkt | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/stdlib/sugar.rkt b/stdlib/sugar.rkt
index 92dcfd5..4802fac 100644
--- a/stdlib/sugar.rkt
+++ b/stdlib/sugar.rkt
@@ -119,7 +119,15 @@
       #:attr id #'x
       #:attr expr #'e
       #:attr type (cond
-                    [(attribute t) #'t]
+                    [(attribute t)
+                     ;; TODO: Code duplication in ::
+                     (unless (type-check/syn? #'e #'t)
+                       (raise-syntax-error
+                         'let
+                         (format "Term ~a does not have expected type ~a. Inferred type was ~a"
+                                 (cur->datum #'e) (cur->datum #'t) (cur->datum (type-infer/syn #'e)))
+                         #'e (quasisyntax/loc #'x (x e))))
+                     #'t]
                     [(type-infer/syn #'e)]
                     [else
                       (raise-syntax-error
@@ -137,6 +145,7 @@
   (syntax-case syn ()
     [(_ pf t)
      (begin
+       ;; TODO: Code duplication in let-clause pattern
        (unless (type-check/syn? #'pf #'t)
          (raise-syntax-error
            '::