>>f xs = (2,2222) : filter ((/=2) . fst) xs It works but not general as `f` still needs to change other value according to the "KEY". Maybe Data.List will supply what i need.
Ketil Malde-5 wrote: > > zaxis <z_a...@163.com> writes: > >>>>value <- readIORef aaa >>>>writeIORef aaa (f value) > >> then aaa will *point to* a new value. > > Exactly. That's what IORefs are, references pointing to contents that > can be changed in the IO monad. > >> The original value will be Garbage Collected, right ? > > Yes, unless something else is holding on to it. > >> Is [(1,1),(2,2),(3,3)] been regarded as a hash? > > It's a list of pairs. You can treat it as an association list using > e.g. 'lookup' from Data.List, if that's what you mean. > >> If not, what is the best way to change it to [(1,1),(2,2222),(3,3)] in >> function `f` ? > > Not sure if there's anything in Data.List, but you could do something > like: > > f xs = (2,2222) : filter ((/=2) . fst) xs > > -k > -- > If I haven't seen further, it is by standing in the footprints of giants > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- View this message in context: http://www.nabble.com/How-can-i-safely-change-the-value-of-specified-key---tp26005244p26006947.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
