Formal comment #193 (enhancement)

proc in hash-table-update! should not mutate hash-table
Reported by: 	Daniel Villeneuve
Version: 	5.92


SUMMARY

The callback procedure of the hash-table-update! function should be
restricted to not mutate the hash-table being updated.

DESCRIPTION

The advertised goal of hash-table-update! is to allow an
implementation to provide a more efficient update algorithm than the
one proposed in the Standard.

Such extra efficiency is presumed to come from the implementation
remembering the "entry" found by the underlying call to hash-table-ref
and reusing this entry in the underlying call to hash-table-set!.

But this remembering seems unsound if <proc> can call
(hash-table-delete! ht key) or (hash-table-clear! ht).

PROPOSAL

Add "<proc> must not mutate the hash-table" as in the specification of
map.


RESPONSE:

In the next draft of the Report, language will be added to the effect 
that "<proc> should not mutate the hashtable".