[Haskell-beginners] Why is there no notion of a one-tuple (e.g.,
a '()' as opposed to a '') in Haskell?
Ben.Lippmeier at anu.edu.au
Thu Sep 25 00:23:51 EDT 2008
On 25/09/2008, at 11:27 AM, ajb at spamcop.net wrote:
>>> Haskell doesn't have a notion of a one-element tuple.
>> Why not?
> Perhaps more crucially, it's hard to see where such a thing would
> be useful.
IORef, and ML's ref types are sort of one element tuples. The ML ref
type is more so, because you don't need a special monad to read and
write its contents..
Ref types are useful because many different parts of your program can
hold pointers to the outer constructor. By updating the constructor to
hold a different value, you propagate this new value throughout your
program in a single, constant time operation.
Ref types can be very useful in practice. IORefs are used GHC's type
inferencer to implement type substitution. They're also heavily used
in interactive programs like frag to propagate the current user
input state throughout the program.
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