add symbol table demo file

demos/symbol-tables.rkt

@@ -0,0 +1,55 @@
+#lang racket
+
+(module lang racket
+  (require "../main.rkt")
+  (provide my-define my-ref Number List)
+
+  (begin-for-syntax
+    (define-persistent-symbol-table types))
+
+  (syntax-spec
+    (nonterminal type
+      Number
+      (List t:type))
+
+    (binding-class my-var)
+
+    (host-interface/definition
+     (my-define x:my-var t:type)
+     #:binding (export x)
+     #:lhs [(symbol-table-set! types #'x (syntax->datum #'t))
+            #'x]
+     #:rhs [#'7])
+
+    (host-interface/expression
+     (my-ref x:my-var t:type)
+     (when (not (equal? (symbol-table-ref types #'x) (syntax->datum #'t)))
+       (raise-syntax-error #f "type error" #'x))
+     #'x)))
+
+(module def racket
+  (require (submod ".." lang))
+  (provide x)
+  (my-define x Number)
+  ;; =>
+  #;(begin
+      (define-syntax x (syntax-spec-binding my-var))
+      (define x^ 7)))
+
+(module ref racket
+  (require (submod ".." lang) (rename-in (submod ".." def) [x y]))
+  (my-ref y (List Number))
+  ;; =>
+  #;x^)
+
+(require 'ref)
+
+#;(
+   (my-define x t)
+   ->
+   (begin
+     (define x^ 7)
+     (begin-for-syntax
+       (free-id-table-set! ids #'x #'x^)))
+
+   )