[plt-scheme] What is the role of promise and force?

On Sun, 6 May 2007, Grant Rettke wrote:

> What is the role of promise and force?
>
> This weekend I read the R5RS spec. Before then I hadn't heard anything 
> about promise and force, in other words, they don't get blogged about or 
> written up much. Why not? Are they important? For what kinds of things 
> are they used?

Hi Grant,

Maybe this might help?

http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-24.html#%25_sec_3.5

It's all about streams, which tries to deal with modeling the state of a 
system without doing explicit mutation.  A little of the way through the 
chapter, it will discuss how we might implement streams by using DELAY and 
FORCE as our primitives for implementing streams.