[Haskell-cafe] memorize function with number parameterized types in GHC

[Bin Jin]

Hi,
Then how about p2num, how to memorize this function.

Also I think it's okay to memorize this kind of function. The type system
ensure all calling of montgKeys have the same type, e.g., it's a pure
function without parameter, it's safe to memorize it since it didn't occupy
more memory than representing dynamic generated types.
On Nov 6, 2011 11:06 PM, "Yucheng Zhang" <yczhang89 at gmail.com> wrote:

> On Sun, Nov 6, 2011 at 9:35 PM, Bin Jin <bjin1990 at gmail.com> wrote:
> > Hi,
> > Since I actually didn't use the parameter in calculation, the return
> value
> > only depends on the type
> > of input, not the actually value. If it's impossible to cache the
> result, is
> > there another way to
> > memorize this "function" ?
>
> Sorry, I haven't considered about 'number parameterized
> type' when I answered the question.
>
> However, you can still use a data structure like MemoTrie [1]
> to memorize the function. The memorization is trivial, since
> you can convert between the number-typed 'undefined' and
> 'Integer' with the functions 'p2num' and 'num2p' in your
> code. I've not tested, but this is an example using MemoTrie:
>
> > import Data.MemoTrie
> >
> > memoMontgKeys :: (PostiveN p, Integral a, Bits a) => p -> a
> > memoMontgKeys = memoMontgKeys' . p2num
> >
> > memoMontgKeys' :: (Integral a) => Integer -> a
> > memoMontgKeys' = memo (montgKeys . num2p)
>
> On the other hand, I think GHC is not expected to do the
> memorization automatically. An arbitrary number can turn up
> as the argument type of 'montgKeys'. This is similar to a
> function with an Integer argument, which GHC does not
> memorize now.
>
>
> [1] http://hackage.haskell.org/package/MemoTrie
>
>
>
> Yucheng Zhang
>
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