Should findIndex return Maybe Number instead of failing with -1?

[sharkdp]

Let me start by saying that I really like how head, tail and other functions in this module are safe by default (compared to Haskell). Considering this, it seems strange to me that findIndex (and three related functions) have the type

findIndex :: forall a. (a -> Boolean) -> [a] -> Number

and fail with -1. While this is technically not 'unsafe' behavior, the -1 should not be used as an array index. Right now, I don't see how the -1 value is useful other than signalling failure. For me, it would feel more natural if the type would simply be

findIndex :: forall a. (a -> Boolean) -> [a] -> Maybe Number

and failure would be indicated by Nothing.

[paf31]

👍 Sounds good to me.

[garyb]

We could also change it to use Int from purescript-integers instead of Number perhaps, as we're adding the compiler optimisation for integers now.