[Haskell-cafe] Re: Processing of large files

[Tomasz Zielonka]

On Thu, Nov 04, 2004 at 11:44:32AM +0300, Alexander Kogan wrote:
> Ok. 
> I have 2 questions about this:
> 1. This means seq function evaluates only 'top' of argument, so when I pass, 
> for example, list as argument, it will be evaluated only to [unevaluated, 
> unevaluated, ...]? Am I right?

Almost. [...] is a syntactic sugar. List is defined by an algebraic data
type:

    data [a] = (:) a [a] | []

seq'ing a list will only force the topmost constructor, ie:

    unevaluated : unevaluated

or 

    []

or
    _|_

Note that the things marked 'unevaluated' above, could be already
evaluated by some other computation.

> 2. If so, is there method to _completely_ evaluate expression?

Most of the time you don't need it. But if you think you do, search
for DeepSeq. I think that Data.Generics could be also used for that.

Best regards,
Tom

-- 
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