Garbage Collection

Almost all other implementations of Lisps assign variables differently to ours. They do not store a copy of a value in the environment, but actually a pointer, or reference, to it directly. Because pointers are used, rather than copies, just like in C, there is much less overhead required when using large data structures.

Garbage Collection • Pick up that can.

If we store pointers to values, rather than copies, we need to ensure that the data pointed to is not delete before some other value tries to make use of it. We want to deleted it when there are no longer any references to it. One method to do this, called Mark and Sweep, is to monitor those values that are in the environment, as well as every value that has been allocated. When a variable is put into the environment it, and everything it references, is marked. Then, when we wish to free memory, we can then iterate over every allocation, and delete any that are not marked.

This is called Garbage Collection and is an integral part to many programming languages. As with pool allocation, implementing a Garbage Collector does not need to be complicated, but it does need to be done carefully, in particularly if you wish to make it efficient. Implementing this would be essential to making this language practical for working with large amounts of data. A particularly good tutorial on implementing a garbage collector in C can be found here.

This should interest anyone who is concerned with the language’s performance and wishes to change the semantics of how variables are stored and modified in the language.