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The general consensus in the community afaik, is that head :: [a] -> a in Prelude was a mistake, and the default should be to return a Maybe/Optional. Begin
by sullyj3 6y ago
The general consensus in the community afaik, is that
head :: [a] -> a
in Prelude was a mistake, and the default should be to return a Maybe/Optional. Beginners are generally advised to avoid head, and all other partial functions in the Prelude, such as tail and the indexing operator, wherever possible, and rely on pattern matching instead, which is generally sufficient and more idiomatic for the relevant use cases. I agree that having the option to use a partial function is useful, escape hatches are important, but it shouldn't be the go to.
Nonempty was just a simple example. You're right that it's not very commonly used (probably because it's not in Prelude), but the general culture of writing type safe interfaces and pushing guarantees to compile time %100 is a thing. A commonly used, more complicated example might be Servant, which is a web library which statically ensures your implementation meets an API spec.
- tsimionescu 6y agoWell, since the Prelude was never changed to at least add an alternative headMaybe, perhaps it was not seen as a deep enough mistake. Yes, I am aware that the Haskell community generally tries to push more guarantees to compile time, and that Haskell's ease of defining and using new types equivalent to existing ones but that signify some property helps a lot in this. Still, there is some limit to this. For example, you have many libraries adding measurement units for Haskell, and many libraries doing linear algebra. But you won't find too many people doing linear algebra with measurement units, because the types of intermediate results explode too much (e.g. a type-safe unit-of-measurement matrix multiplication of 3x3 matrices has 18 type parameters, with complicated restrictions between them).
- sullyj3 6y agoDefinitely don't disagree!