[Haskell-cafe] Re: Making monadic code more concise

Alexander Solla ajs at 2piix.com
Tue Nov 16 15:40:47 EST 2010

On Nov 16, 2010, at 12:36 PM, Ling Yang wrote:

>  Are only
> 'trivial' results possible, or that the incomputability problems are  
> just moved
> into type space?

That's typically the case, under Rice's theorem.

A construct is derivable if it works for all cases (i.e., it's a "free  
theorem"), or if it works for none.  If it works for some, you need to  
encode the differences between the cases yourself.

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