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Comment by notallama | Hacker News Reader

does this guy not know how to use type declarations?

[1,2,3,4,5] :: [Int] problem solved!

He knows, as it is clearly visible in his article. His point is, he should not need to.

This is a property of many statically typed languages, and Haskell isn't known for being one of the more forgiving languages in that family.

I appreciate that his goals were more mathematically oriented than not, but surely he would've seen something like this coming?

Actually, you don't need to in most real programs. You usually use the elements of a list with some function that makes it clear what type they have.

In GHCi (the interpreter) this doesn't happen. It has some defaulting rules to alleviate this, but I don't quite understand them, so I can't say why they didn't kick in in this case.

The thing with Haskell is that it doesn't automatically coerce types the way other languages do. It uses Hindley-Milner type inference up front if you don't specify your types, but this is far from foolproof. Once it's decided you're using type Foo, you're stuck. You need explicit typing in many cases.

One of the first things you learn as a Haskell programmer is to treat type inference with suspicion.

Languages like SML and OCaml also use this sort of type inference, but you tend to not need type annotations in those languages except in very special cases. I think this is also fairly true of Haskell -- type inference works in 99% of the cases, and explicit type annotations are just a stylistic thing.

Most of the time you're right. But I've done a fair bit of tinkering with Haskell's OpenGL library. Trying to get GHC to differentiate between a Float and a GLfloat inside a Vector is pretty much impossible without resorting to explicit typing. This definitely qualifies as a special case, but it's cropped up often enough as to make me a little gun shy. You don't need to explicitly type everything, just enough to give the compiler a credible hint as to what you're trying to do -- such as the last term in your vector.

The sad thing about the original article is that the writer is throwing his hands up and raging over what is really a small implementation hiccup. I kind of like that the compiler withholds judgment on whether '5' is a Float, Int, or Integer. It means that I no longer need to type ".0" after every Float.

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