[Haskell-cafe] generalized list comprehensions
duncan.coutts at worc.ox.ac.uk
Mon Nov 10 13:51:34 EST 2008
On Mon, 2008-11-10 at 18:19 +0000, Andrew Coppin wrote:
> I don't actually use *lists* all that much - or at least not list
> transformations. And if I'm going to do something complicated, I'll
> usually write it as a do-expression rather than a comprehension.
> > Just a random example out of Cabal:
> > warn verbosity $
> > "This package indirectly depends on multiple versions of the same "
> > ++ "package. This is highly likely to cause a compile failure.\n"
> > ++ unlines [ "package " ++ display pkg ++ " requires "
> > ++ display (PackageIdentifier name ver)
> > | (name, uses) <- inconsistencies
> > , (pkg, ver) <- uses ]
> > Pretty concise and clear I think.
> Erm... yeah, it's not too bad once I change all the formatting to make
> it clear what's what.
> Wouldn't it be a lot easier as a do-block though?
I don't think so:
++ unlines $ do
(name, uses) <- inconsistencies
(pkg, ver) <- uses
return $ "package " ++ display pkg ++ " requires "
++ display (PackageIdentifier name ver)
Of course reasonable people may disagree. It's mostly aesthetics.
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