Haskell's lazy-by-default evaluation makes it more difficult to reason about memory usage, because it is all too easy to accidentally build up large expression

Haskell's lazy-by-default evaluation makes it more difficult to reason about memory usage, because it is all too easy to accidentally build up large expression trees at runtime [1]. This makes it a rather bad choice for a kernel or other low-level stuff. Compare Rust, which tries to keep allocations (and the size/asymptotic complexity of allocations) explicit and visible. [1] The optimizer catches some cases, but not all of them.