How lazy is DData.Seq?

JP Bernardy jyp_7 at
Sun May 9 16:14:20 EDT 2004

--- Wolfgang Jeltsch <wolfgang at> wrote:

> Hi,
> meanwhile, I'm not sure if I need lazyness in my
> concrete example.  But the 
> general point is the following:
> I have functions for converting values of certain
> data types to strings.  I 
> don't use [Char] but Seq Char as the result type of
> these functions to allow 
> for efficient concatenation.  For one concrete type
> I want to test if the 
> values of this type have a certain property.
> I use the to-string conversion function to check for
> this property because a 
> value has the property in question iff the first
> character of the string 
> representation is a letter.  So I want to do
> something like
>     isAlpha $ head $ toString value.
> toString value is constructed by multiple
> applications of append, so it may in 
> the end be something like
>     append (append a (append b c)) (append (append d
> e) f).
> In this example I'd want the terms
>     append b c
> and
>     append (append d e) f)
> to not be evaluated at all.

Ok, I think was mistaken in this respect.

The current version behaves ok for sequences mainly
constructed with fromList, cons or snoc; a sequence
made up of 'append' is strict.


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