[Haskell-beginners] question on types

[Daniel Fischer]

On Friday 29 July 2011, 03:26:33, Jake Penton wrote:
> 
> Ok, thanks. I have some studying to do about haskell types, clearly.
> 
> Does that mean then that there is no definition possible of f other than
> 'undefined'? I mean this compiles:
> 
> f::a
> f = undefined
> 
> But is there any other possible second line defining f?

Sure, you can write the same thing in many different ways:

f :: a
f = f

f :: a
f = let x = x in x

f :: a
f = error "Foo"

but all definitions of "f :: a" that compile yield (some kind of) bottom, 
since _|_ is the only value that is common to all types (whether an attempt 
to evaluate such a value yields actual nontermination or an exception 
message depends; the first two don't terminate in ghci but result in 
"<<loop>>" when used in a compiled programme).

> 
> - Jake -