On 28 September 2004 05:43, Ben Rudiak-Gould wrote:
On Mon, 27 Sep 2004, Einar Karttunen wrote:
I recently noticed that Data.HashTable silently accepts duplicate keys and keeps all the values. This is very counterintuitive from the interface and makes updating a hashtable quite tedious (lookup + delete + insert).
OCaml's Hashtbl also works this way. It makes sense if you think of a hash table as a speedier drop-in replacement for an association list: Data.HashTable.insert behaves like consing a new (key,val) pair onto the front of an association list, and Data.HashTable.delete and Data.HashTable.lookup behave like the corresponding list functions. I agree 100% that it should be documented, of course.
However, playing around with HashTable just now, I noticed the following (GHCi):
Prelude> hash <- Data.HashTable.fromList id [(1,'a'),(1,'b')] Prelude> Data.HashTable.lookup hash 1 >>= print Just 'b'
This is clearly wrong, and makes me think that Data.HashTable's behavior given identical keys wasn't well thought out. I'm in favor of plagiarizing OCaml's Hashtbl interface, which has the update function (called replace) as well as other useful operations like copy and find_all.
By all means go ahead and fix this, I won't have time to look into it in the short term. Cheers, Simon