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.
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