On 27 Mar 2008, at 15:32, Luke Palmer wrote:
More to the point, if List is declared as:
newtype List a = List (Integer -> a)
Instead of with "data", it also works.
The problem, as was stated, was that -+ is too strict. That is, without the ~ there, -+ evaluates its right argument to make sure it's not _|_ (that is the only other possibility in this case), and then proceeds with the rest of the function. So in:
h x = first x -+ h (rest X)
This first evaluates the recursive call, which will evaluate the recursive call, which ...
Thank for the suggestion, and explanation. The reason I used a "data" construct was that I include the size of the list, excluded in order to keep the example as simple as possible: data List a = List(Ordinal -> a, Ordinal) In addition, there seems to be no way to choose default value for a given (non-empty) type in Haskell, so I wrote it data List a = Empty | List(Ordinal -> a, Ordinal) Here, if a type T has a default element t, I can represent the empty list by List(\_ -> t, 0) making the constructor "Empty" redundant. Hans Aberg