[plt-scheme] How to make unit functors?

From: Matthew Flatt (mflatt at cs.utah.edu)
Date: Wed May 28 18:38:22 EDT 2003

At Wed, 28 May 2003 17:19:18 -0500, Robby Findler wrote:
> Say that I'm implementing a finite mapping data structure that claims
> to map all values, but only creates the actual entries lazily (ie, when
> they are looked up or changed or something like that). If you ask me
> for 'l many times, but I only keep the hash code for 'l in my data
> structure, you may get different entries in the table at different
> times, as the symbol table is gc'd.

I don't quite follow. If you keep only the hash code, how do you know
that it has something to do with 'l (as opposed to, say, 'foo)?

> In some sense, the hash-code is a ptr to 'l that the gc forgets
> about.

This doesn't sound right, mainly because the hash-code-to-value mapping
is not a function.


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