3 ms·

intuition about lazy evaluation order can be very misleading

• AnimalMuppet 11y ago
  Is it fair to say that in Haskell, you have to think about evaluation order less, but when you do, it's harder?
  • jonnybgood 11y ago
    When you hit that difficult to reason about evaluation order in Haskell, it'll take that time you thought you gained.
  • oconnore 11y ago
    I think it can be unexpected if you're used to other semantics, but the behavior of laziness is very well defined. > let x = [1 .. 100] :: [Int] > seq x () -- force the first cons > :sprint x x = 1 : _ -- we evaluated the first cons > foldr (\e l -> e + l) 0 x 5050 -- printing this value forces foldr to complete > :sprint x x = [1,2,3,4,5...100] -- all conses evaluated
• safewayclubcard 11y ago
  I agree with this statement. I think lazy evaluation is very hard, especially when you are dealing with a codebase of of say 50 files with structures containing other structures, the line between lazy and strict is very hard to see. The difficulty learning lazy evaluation skill goes from * 0 where you know nothing to 5 where you sort of understand. * 5 - 90 is a space where you think you know what it is, but you really don't. You'll probably get yourself in trouble more than helping. * 90-100 is when you grok it and can use it effectively. I am an avid haskell user for a few years and I am still 50/50 on most of my conclusions about laziness without asking someone else.