Fwd: [Haskell-cafe] Re: Why?
Alberto G. Corona
agocorona at gmail.com
Thu Dec 10 09:37:53 EST 2009
My understanding is that a pointer to the lazy expression tree for the
calcualtion of the parameter is put it the corresponding location of the
function expression tree. But at any time you can force the evauation before
the call. or the compiler itself. Optimization is possible depending on the
knowledge. What happens if the parameter is a large list and the function
handles a few elements?.
All of these consideration pales when a programmer has to call a procedure
in a library made by others with no documentation, and no clue about what
the procedure does inside. The purity and the type system removes many
2009/12/10 David Leimbach <leimy2k at gmail.com>
And that would be true if everything were strict and not partially evaluated
> sometimes :-)
> My understanding is the following... (and I could be way off)
> Remember that a function of arity N is really N functions of arity 1 with
> their arguments bound one at a time to create a new function along the way.
> At least you *can* write your code that way if you really want to, but the
> laziness might make it such that all the parameters are not bound, due to
> not being "needed" at that moment. Instead a thunk or what some other
> languages might call a "Future" is put in the argument's place, to be
> evaluated when needed.
> If Haskell were strict by default, I think your claim of passing references
> around could be true, but my experience with Haskell has been that sometimes
> it's too lazy for me to write the code that I first thought would be
> efficient without a lot f study and refactoring of that code.
> I'm sure this gets easier with practice, but it's not something I was
> expecting to be as difficult as it all was.
> On Thu, Dec 10, 2009 at 5:57 AM, Alberto G. Corona <agocorona at gmail.com>wrote:
>> One more advantage that is not frequently cited
>> Purity permits to pass every parameter of a procedure by reference
>> (giving the pointer) rather that by value giving a copy, and still be sure
>> that the data has not been modified. Besides the safety. this is great
>> language optimization itself.
>> 2009/12/10 Alberto G. Corona <agocorona at gmail.com>
>>> What material benefit does Haskell derive from being a "pure" functional
>>> language as opposed to an impure one?
>>> Here is my list of benefits of purity (some of them are enhanced by other
>>> features like the type system).
>>> Purity means referential transparency. that means that the programmer
>>> has no way to modify pure data. That cut the tree of possible programmer
>>> errors.In particular, since there are no variables, every state change must
>>> be in the form o a call to a function with new parameters. each function has
>>> no state change (except when needed and then the type system labels the
>>> stateful code as such)( This enforcement goes in the righ direction for
>>> clarity and readability, maintainability, modularity xxxxxbility.
>>> Purity also eases paralel processing, since no data is modified, each
>>> process is isolated better. Less opportunities for errors.
>>> Purity permits lazines because since the execution tree of
>>> an expression has pure, data, can be evaluated later, since it will not be
>>> Lazy evaluation eases mathematical reasoning,because mathematics has no
>>> notion of eager evaluation, but to make use of mathematical equations when
>>> the calculation is needed. .
>>> Mathematical reasoning permits the full use of a long tradition of
>>> mathematical knowledge. This makes code more simple, understandable,
>>> general, proof guarantted and elegant (for those that know the mathematical
>>> domain). This also permits high level optimization of code, both by the
>>> programmer and the compiler.
>>> for sure there are a few more
>>> We are superstitious and guided by "nonrational" ideas such is beauty.
>>> bauauty -> (simplicity -> (less effort to master, less errors)
>>> , utility ->, solve more problems, solve greater
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