I’m just curious, but is there any practical guide or tutorial on this topic? I found it relatively hard to reason about the time complexity of Haskell programs. — Xiaojun "Phil (http://cnphil.com/)" Hu On Friday, 6 June, 2014 at 21:05, Bob Ippolito wrote:

That declares those fields to be strict. See also http://www.haskell.org/haskellwiki/Performance/Data_types

On Friday, June 6, 2014, Song Zhang wrote:

...

This is about syntax of Haskell. I am reading the source code of Yampa. I find that a definition like the following

data SF' a b where SFArr :: !(DTime -> a -> Transition a b) -> !(FunDesc a b) -> SF' a b

in Yampa.hs.

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I really like the explanation of Haskell's non-strict evaluation from Parallel and Concurrent Programming in Haskell, reading this chapter will probably be sufficient and much easier than studying all of GHC's implementation details: http://chimera.labs.oreilly.com/books/1230000000929/ch02.html#sec_par-eval-w... On Fri, Jun 6, 2014 at 10:15 PM, Kim-Ee Yeoh wrote:

On Sat, Jun 7, 2014 at 11:14 AM, Xiaojun "Phil" Hu wrote:

...

I found it relatively hard to reason about the time complexity of Haskell programs.

Is that the question you really want to ask?

If it is, the answer is trivial: if it's O(f(n)) time in other languages, it's also O(f(n)) time in Haskell. (Note: space is a different story.)

But what typically people want to know is: why is my program so slow?

You wonder about the constants covered up by Big-Oh.

And so you're going to have to get acquainted with

0) lambda calculus 1) graph reduction, 2) the G-machine, and 3) the spineless-tagless variant thereof.

You're also going to have to learn to read Core and understand some of the higher order core-to-core optimizations that GHC performs.

-- Kim-Ee

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