Use current-readtable as the base for the TR readtable.

Closes PR 1115.

collects/tests/typed-scheme/succeed/at-exp.rkt

@@ -0,0 +1,9 @@
+
+#lang at-exp typed/racket
+
+(define contents
+ (lambda args args))
+
+(define doc @contents{x y})
+
+@contents{x y}

collects/typed-scheme/language-info.rkt

@@ -14,5 +14,5 @@
            (require (for-syntax typed-scheme/utils/tc-utils scheme/base))
            (begin-for-syntax (set-box! typed-context? #t)))
         (current-namespace))
-  (current-readtable readtable))
+  (current-readtable (readtable)))
 

collects/typed-scheme/typed-reader.rkt

@@ -72,15 +72,15 @@
       (let-values ([(l c p) (port-next-location port)])
         (list src line col pos (and pos (- p pos)))))]))
 
-(define readtable
-  (make-readtable #f #\{ 'dispatch-macro parse-id-type))
+(define (readtable)
+  (make-readtable (current-readtable) #\{ 'dispatch-macro parse-id-type))
 
 (define (*read inp)
-  (parameterize ([current-readtable readtable])
+  (parameterize ([current-readtable (readtable)])
     (read inp)))
 
 (define (*read-syntax src port)
-  (parameterize ([current-readtable readtable])
+  (parameterize ([current-readtable (readtable)])
     (read-syntax src port)))
 
 (provide readtable (rename-out [*read read] [*read-syntax read-syntax]))