[Haskell-cafe] Re: Can we come out of a monad?
felipe.lessa at gmail.com
Tue Aug 10 17:27:49 EDT 2010
On Tue, Aug 10, 2010 at 6:21 PM, Martijn van Steenbergen
<martijn at van.steenbergen.nl> wrote:
> On 8/2/10 7:09, Ertugrul Soeylemez wrote:
>> Given the definition of a Haskell function, Haskell is a pure language.
>> The notion of a function in other languages is not:
>> int randomNumber();
>> The result of this function is an integer. You can't replace the
>> function call by its result without changing the meaning of the program.
> I'm not sure this is fair. It's perfectly okay to replace a call
> "randomNumber()" by that method's *body* (1), which is what you argue is
> okay in Haskell.
Nope. For example, suppose we have:
int randomNumber(int min, int max);
randomNumber :: Int -> Int -> IO Int
In Haskell if we say
(+) <$> randomNumber 10 15 <*> randomNumber 10 15
That's the same as
let x = randomNumber 10 15
in (+) <$> x <*> x
If we had in C:
return (randomNumber(10, 15) + randomNumber(10, 15))
That would not be the same as:
int x = randomNumber(10, 15)
return (x + x)
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