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Sequences - Unterstanding
f#

Hi.

I have a question regarding F# sequences.

In F# Language Reference they are described like follows: A sequence is a logical series of elements all of one type. Sequences are particularly useful when you have a large, ordered collection of data but do not necessarily expect to use all the elements. Individual sequence elements are computed only as required, so a sequence can provide better performance than a list in situations in which not all the elements are used....

So, suppose I declared the following sequence 

1

let mySeq = seq { for i in 1 .. 100 do yield i * i }

The default depth of a sequence is 4 elements.

Now suppose I want to iterate through first 10 elements, mySeq will be evaluated again, which will generate 10 elements.

Next time I want to iterate through first 50 elements. mySeq will be evaluated again and generate 50 elements. an so on...

Do I understand it right?

Thanks and best regards.

.

An interesting function in this context: Seq.cache, [link:msdn.microsoft.com]

By on 3/9/2011 10:10 AM ()

Hi,

do you know the Iterators of C#? It's more or less the same thing. 'a seq is AFAIK only a short name for IEnumerable<'a>.

So yes if you first take 10 elements of your seq and than again 50 the first 10 will be computed twice.

By on 3/9/2011 3:56 AM ()

Hi,

do you know the Iterators of C#? It's more or less the same thing. 'a seq is AFAIK only a short name for IEnumerable<'a>.

So yes if you first take 10 elements of your seq and than again 50 the first 10 will be computed twice.

Yes, I knew that a seq<a'> is in fact a IEnumerable<'a>. I just wanted to understand the laziness of F# sequences. Thanks.

By on 3/9/2011 4:03 AM ()

The laziness is just the same as with IEnumerable/IEnumerator - you only call MoveNext if you need to.

By on 3/9/2011 6:03 AM ()

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