The compiler can already infer all the types anyways, you don't need to declare types. It is considered good practice (and -Wall warns for it) to provide types for top level definitions, as they are usually important enough to warrant this form of machine checked documentation.
note: Yes I know the compiler can't actually infer all types all the time, but the exceptions are obvious and require type information in dynamically typed languages too (ie. convert a string to an int: you have to tell it you want an int, you can't just say "convert this string" and have it guess what you want it converted to).
It's also pretty easy and useful to step out of the HM, inferable fragment using any number of popular language extensions. I'm not arguing that it's a problem, but it's disingenuous to suggest that anything resembling all code can be type-inferred.
I don't think so. We are talking about haskell after all, not haskell + experimental ghc extensions. And which popular extensions break type inference anyways?
But the cool thing is that in many (most?) cases you can actually infer the type of reading from a string. You are going to do something with that value right? So you can say
1 + (read "1")
and the compiler will know that you must want to read "1" as a number and does that!
Yeah, I most commonly hit "oh, I need to annotate that" when I'm building some expression piece by piece in ghci, and so effectively what I'm doing with that value is "print it, as appropriate to the type" - which doesn't tell us much about what type it is.
That kind inference only works because + is defined to work on Nums only (importing only prelude). You don't even need the initial 1. A nice trick but these are rather small details.
With the caveat that the compiler can come up with A consistent inferred typing, but it may not be the exact type you had in mind, especially when dealing with numerics. This is very rarely a problem, but in some cases may result in less optimized code than might be possible with a stricter annotation.
note: Yes I know the compiler can't actually infer all types all the time, but the exceptions are obvious and require type information in dynamically typed languages too (ie. convert a string to an int: you have to tell it you want an int, you can't just say "convert this string" and have it guess what you want it converted to).