[Haskell-cafe] Is "let" special?

[Henning Thielemann]

On Thu, 4 Nov 2010, Ryan Ingram wrote:

> When you use arrows for your DSL, how do you avoid getting trapped by
> "arr"?  It seems like it's hard to avoid people working arbitrary
> functions into your computation using it.

I use this for instance in synthesizer-llvm. Actually people can lift 
anything into the arrow, but in the end there is a run function that 
expects an arrow of type

   Arrow (Value a) (Value b)

where (Value a) denotes a virtual LLVM register that holds a value with a 
type equivalent to the Haskell type 'a'. There are functions like (\a -> 
(a,a)) that can be lifted to the arrow and that make sense. But e.g. there 
is no (uncury (+)) for Value.