On 24 May 2011 13:41, Johannes Waldmann
I could just store the length of the list - as an additional argument to the "Cons" constructor that is automatically initialized on construction (and you never need to change it later, since Haskell objects are "immutable", in the words of Java programmers)
In Haskell, the reason for not doing this (besides simplicity, and inertia) actually is (I think) laziness: you don't want to evaluate the "length" field of the second argument of the "cons" prematurely.
Neither OCaml nor PLT Scheme cache the length or they didn't a year of two ago when someone asked this question on the Haskell Beginners list and I checked the respective source trees. As the PLT Scheme list was implemented in C at the time (maybe it still is?) I was a bit surprised by this.