Re: [Haskell-cafe] What's the deal with Clean?

Really, arrays in Haskell are the most @#!$! confusing thing in the world. There's a bunch of different array structures. I can't tell which one works best, and all I want to do is x[i] = value. I thought uvector was the answer, you know, fast unboxed ARRAYs. Imagine my surprise when I saw this indexU :: UA e => UArr e -> Int -> e O(n). indexU extracts an element out of an immutable unboxed array. An array implementation with an order N lookup. huh ?? That's not an array, that's a list. I was looking for an array. However, I then found in the same hackage: readMU :: MUArr e s -> Int -> ST s e O(1). readMU reads the element at the specified index of a mutable unboxed array. So O(1) for mutable, but O(n) for immutable ? See, confusing... I'm sure there's a really good, lofty type safety, something or other reason for that, that I'm sure I don't care about ;-) There's also ST. So why is there a uvector, when there's ST ?? etc, etc, etc... and then there's monads... other than that, having fun with haskell :-) Brian On Nov 3, 2009, at 3:42 PM, David Leimbach wrote:

On Tue, Nov 3, 2009 at 2:16 PM, Tracy Wadleigh

...

wrote:

I had to implement a ring buffer, and I wanted the code using it to be written in Haskell. I ended up implementing the buffer in C, and wrapping it in FFI from Haskell because implementing a destructive array in Haskell is kind of unwieldy to someone of my experience level. In Clean, it looks like the uniqueness typing allows for destructive updates in a very controlled manner.

The ST monad provides this functionality. The never-instantiated-in- a-visible-way state parameter of the ST monad provides the "uniqueness" required for doing destructive updates in a pure way.

Someone suggested that to me on IRC once I'd already cranked out a C implementation with FFI bindings. It's just too easy to use the FFI in Haskell :-)

If we raise the barrier of FFI, more people will use ST!

Dave

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