Note that although serializing simple values (like numbers and symbols) to urls works, serializing big data doesn't work because urls have a length limit. What

Note that although serializing simple values (like numbers and symbols) to urls works, serializing big data doesn't work because urls have a length limit. What I was trying to explain is a system that stores the data on the server and passes pointers to this data to the client. Web applications that use databases already work this way. The id/primary key column of a database table is the pointer. To serialize a closure you generate ids for the values of the free variables. Then you save the values in a hash table and send the ids to the client (instead of the actual values). To deserialize a closure you fetch the free variables from the hash table. This system doesn't work yet because this hash table keeps growing. Every time you serialize a closure you put the free variables in the hash table. This is wasteful because some of the values might already be in the hash table. This is simple to fix; just look if the value is in the hash table, and if it is you return the existing id (this can be done efficiently by having two hash tables: ids->values and values->ids).