Hi Matthew - thanks for the tip and I will experiment with it. Thanks, yc <div>On 8/15/07, Matthew Flatt <<a href="mailto:mflatt@cs.utah.edu">mflatt@cs.utah.edu </a>> wrote:<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">At Wed, 15 Aug 2007 01:23:01 -0700, YC wrote: > Of course - any data stored in a hash table would live until the hash table > goes out of scope or until the data gets overwritten, and it doesn't obey > lexical rules. > > Are there ways to make it obey lexical rules so the register can behave more > like an actual symbol table?   i.e. if a type is declared within a lexical > scope as it goes out of scope the value is removed from the register.  I > assume that if this is possible there needs to be a way to know that I'm in > a different lexical scope then before. See `make-bound-identifier-mapping'. There's no way for bindings to get dropped from the table, but scope should work out right. Also, when compiling modules, a fresh module instantiation for each expand/compile will effectively clear the table each time you expand/compile a module. Matthew </blockquote></div>