[Haskell-cafe] mapM is supralinear?

Tim Docker tim at dockerz.net
Wed Sep 21 14:57:01 CEST 2011

On 09/09/2011, at 8:19 PM, John Lato wrote:

> Agreed.  Whenever I'd like to use mapM (or any other function for
> which a *M_ is available), I've found the following rules helpful:
> 1.  If I can guarantee the list is short (~ n<=20), go ahead and use  
> mapM
> 2.  Otherwise use mapM_, foldM_, or foldM if a real reduction is
> possible (i.e. not "foldM snocM []").
> Step 2 sometimes requires changing my design, but it's always been for
> the better.  `mapM_` tends to require more pipeline composition, so
> it's leveraging the language's strengths.

This thread is really interesting - it relates directly to problems I  
am currently
having with mapM over large lists (see the thread "stack overflow  

Can you explain what you mean by "mapM_ tends to require more pipeline  
In what way is it leveraging the language strengths?



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