TIL: wrapping list comprehension in a function can prevent fusion
TIL: wrapping list comprehension in a function can prevent fusion
This fuses:
[(x, y) | x <- [0 .. 10], y <- [0 .. 10]]
But this does not:
liftA2 (,) [0 .. 10] [0 .. 10]
Because the latter inlines to:
let xs = [0..10]; ys = [0..10] in xs >>= \x -> ys >>= \y -> (x, y)
And GHC is afraid to push the ys binding into the \x -> ... lambda because that might duplicate the work of evaluating [0..10]. Even though in the end fusing everything would be beneficial.