Quick, an Ocaml quiz:

What is the best way to write a summation function?

let sum a = List.fold_left (fun x total -> x+total) 0 a

let sum a = List.fold_right (fun x total -> x+total) a 0

let plus1 a = List.map (fun x -> x+1) a

let plus1 a = List.rev_map (fun x -> x+1) a

Answer: fold_left and rev_map.

Why? Because fold_left and rev_map are tail recursive, and therefore a) faster, b) use less resources, and c) don’t blow up when you pass a large list. Don’t get me started on the fact that the default List.map is implemented as a recursive procedure!

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