[Haskell-cafe] Seen on reddit: or,
foldl and foldr considered slightly harmful
ketil at malde.org
Thu Feb 11 05:00:51 EST 2010
Johann Höchtl <johann.hoechtl at gmail.com> writes:
> In a presentation of Guy Steele for ICFP 2009 in Edinburgh:
> he "considers foldl and foldr" harmful as they hinder parallelism
> because of "Process first element, then the rest" Instead he proposes
> a divide and merge aproach, especially in the light of going parallel.
In Haskell foldl/foldr apply to linked lists (or lazy streams, if you
prefer) which are already inherently sequential, and gets a rather harsh
treatment. I notice he points to finger trees, which I though was
implemented in Data.Sequence.
> are somewhat geared towards Fortress, but I wonder what Haskellers
> have to say about his position.
Can we (easily) parallelize operations on Data.Sequence? Often, the
devil is in the details, and there's a lot of ground to cover between
'trees are easier to parallelize' to an efficient and effective high
level interface. (E.g. non-strict semantics allowing speculative
evalutaion - you still need to insert manual `par`s, right?)
If I haven't seen further, it is by standing in the footprints of giants
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