Problem with Lazyness

gistfile1.idr

-- Only works in the REPL, compiled code explodes with SIGABRT
-- or SIGSEGV

-- Does not terminate
nats : Stream Nat
nats = 0 :: map (+1) nats

mapi : List a -> List (Nat, a)
mapi xs = mapi' nats xs
  where mapi' : Stream Nat -> List a -> List (Nat, a)
        mapi' _ []                = []
        mapi' (n :: ns) (x :: xs) = (n, x) :: mapi' ns xs

{-
-- Works
nats : Lazy (List Nat)
nats = 0 :: map (+1) nats

mapi : List a -> List (Nat, a)
mapi xs = mapi' nats xs
  where mapi' : Lazy (List Nat) -> List a -> List (Nat, a)
        mapi' _ []                = []
        mapi' (n :: ns) (x :: xs) = (n, x) :: mapi' ns xs
-}