On 9 dec 2008, at 09:11, John Ky wrote:
Hi,
I'm looking for a function for Data.Map that will insert a new key and value into the map if the key doesn't already exist in the map. When the key already exists, I don't want the value updated in the map. Additionally, I want to know whether the key/value was inserted or not so that I can return that fact as a boolean from my function.
I can't work out which function in Data.Map is suitable for this task and I wanted to avoid two lookups.
Data.Map.insertLookupWithKey (\k n o -> o) should do the trick. The first element of the tuple returned is the Maybe a that is Nothing if no value existed at the given key, the second element is the updated map. With kind regards, Arthur. -- /\ / | arthurvl@cs.uu.nl | Work like you don't need the money /__\ / | A friend is someone with whom | Love like you have never been hurt / \/__ | you can dare to be yourself | Dance like there's nobody watching