4 ms·

Haskell is lazy and pure, why can't it auto memoize for us so we can code it like we would in math?

• albertzeyer 12y ago
  A while ago, I asked exactly that question: http://stackoverflow.com/questions/5749039/automatic-memoizing-in-functional-programming-languages http://stackoverflow.com/questions/5749039/automatic-memoizi... I think the answer is basically that there is no good heuristic about what to store, how much and how long.
  • cabalamat 12y ago
    > I think the answer is basically that there is no good heuristic about what to store, how much and how long. In Python you can just put a @memoize decorator before a function you want memoized; would it be possible to have something similar in Haskell?
    • albertzeyer 12y ago
      Yes, see here: http://www.haskell.org/haskellwiki/Memoization http://www.haskell.org/haskellwiki/Memoization Note that in Python, you also have the issue that you still need to specify some cleverness about how long something is stored and what is stored. Many example memoize implementations just store everything (e.g.: https://wiki.python.org/moin/PythonDecoratorLibrary#Memoize https://wiki.python.org/moin/PythonDecoratorLibrary#Memoize) but of course that is not a solution in practice.
      • gizmo686 12y ago
        I don't think the methods mentioned in the haskell wiki are quite equivelent to the python decorator, as they require you to modify the data structure itself to support memoization. It should be possible to use UnsafePerformIO to create a generic function memoize function (at least for inputs that implelemt Eq or Ord), but that is almost definantly overkill and asking for space leaks.