Is this a silly question?

[emfanitek]

In groovyx.comprehension.extension.ListComprehensionExtension you use the following code:

static List bind(List self, @DelegatesTo(List) Closure c) { // Haskell's >>=
    c.delegate = self
    self.collect(c).inject([], {acc,elem->acc+elem})
}

What do you gain by using inject after collect? This creates a new list, that is identical to the original collected list.

[uehaj]

Hi, In short, the purpose of inject is flatten the list. In Scala, bind is called 'flatMap' means "Apply map and then flatten". So in this case inject make the list flatten.

  [[1,2,3], [4,5,6]].inject([], {acc,elem->acc+elem}) == [1, 2, 3, 4, 5, 6]

In haskell, list is a instance of monad with definition of '>>=' in following:

instance Monad [] where
  m >>= f  = concat (map f m)  -- map(==groovy's collect) and then flatten by concat
  return x = [x]
  fail s   = []