Re: [MIT-Scheme-devel] specifying hash table weakness

[Taylor R Campbell]

   Date: Sat, 14 Aug 2010 19:20:06 -0700
   From: "Arthur A. Gleckler" <address@hidden>

   > (MAKE-x-HASH-TABLE* <weakness> #!OPTIONAL <initial-size>),
   >  x \in {EQ, EQV, EQUAL, STRING}

   I wonder whether it makes sense to make X a parameter, too.  That
   wouldn't prevent special treatment of EQ.

That would require adding some more parameters, unless there is only a
fixed set of valid arguments for x so that the appropriate values for
the other parameters can be chosen like in SRFI 69 implementation.
Personally I prefer encoding such limited choices in the names -- if
you can pass a procedure, it is tempting to pass a procedure outside
the allowed set, and the subsequent failure is confusing.

We could have a procedure

(MAKE-HASH-TABLE* <key=?> <key-hash> <rehash-after-gc?> <weakness> 
<initial-size>)

or something, too.

   The other obvious possibility is to make a hash table constructor
   maker, i.e. to curry the construction of hash tables, e.g.:

     ((make-hash-table-constructor comparator weakness) initial-size)

   That requires the addition of the fewest new identifiers.  We can
   watch to see which combinations are actually used and then make
   shortcut identifiers for them.

This is what the proposed HASH-TABLE-CONSTRUCTOR already does, except
that it has two more parameters, for the hash function and for whether
the hash function is altered by garbage collection.