Lazy evaluation

gistfile1.hs

-- In GHCi
:set +m
let x y = x y
-- ex: x 2 will loop infinitely

:{
  let {
    z y = y
      where
        t = x 2
  }
:}
-- ex: t = x 2 *would* loop infinitely if strictly evaluated, but doesn't because of lazy evaluation

z 2
-- returns 2
z 7
-- returns 7

-- the expression t = x 2 becomes a thunk and introduces space complexity to the function
-- lazy evaluation in haskell can make code more elegant, but otherwise make it difficult to evaluate the time and (particularly the) space complexity of your programs