[Haskell-cafe] There is no null; Maybe/Option types

[wren ng thornton]

On 4/26/11 9:55 AM, Ertugrul Soeylemez wrote:
> wren ng thornton<wren at freegeek.org>  wrote:
>
>> But the greatest thing about Maybe is that you don't *have* to write
>> code in monadic style. Because Maybe makes explicit the null-pointer
>> shenanigans in other languages, you can simply unwrap the Maybe and
>> pass around the raw value instead of letting Nothing permeate your
>> whole program. Spending all your time in the Maybe monad is just as
>> bad as spending all your time in the IO monad.
>
> Unless you're saying that I'm one of the worst Haskell programmers in
> the world,

Hardly. Never having seen your code that would be most uncharitable.

> you are totally wrong.

I'm not sure I see how that follows.

> Monads are an abstraction for convenience and beauty in expression,

This I agree with...

> not for encapsulating bad habits.

...this, not so much. Though I would phrase my negation differently. It 
is not the habits which are encapsulated, it is merely the effects. And 
the effects which are encapsulated are not "bad", per se. For example, 
GHC uses a prodigious amount of mutation under the covers, and we're all 
glad it does! The point is rather that effects like these make reasoning 
difficult. Thus, in order to keep our programs reasonable it behooves us 
to find ways of restricting the scope of these effects ---not because 
the effects are an evil taint that cannot be allowed to spread, but--- 
because it is easier to reason about code which does not make excessive 
use of them.

Effects like mutation, failures, capturing the current continuation, etc 
are all just tools. And like any tools they can be used both for great 
good and for great evil. Knowing that some segment of code does not use 
them means that we needn't worry about there being devils there, but it 
also means we don't have to worry about there being angels. In my 
experience, the angels can wreak just as much havoc as the devils. 
Angels are often inscrutable and too clever to be deciphered by mere 
mortals; and angels have ingenious ways of working around laws I would 
like to set in stone. When I would like to exclude certain kinds of 
behavior, divine grace can be just as damaging as a trickster.

-- 
Live well,
~wren