[Haskell-cafe] Re: Re-order type (flip map)
dan.doel at gmail.com
Sun Oct 10 21:02:43 EDT 2010
On Sunday 10 October 2010 5:32:16 pm Johannes Waldmann wrote:
> I mean instead of h . g . f $ x
> I'd sometimes prefer x ? f ? g ? h
> but what are the "?"
Note, before anyone gets too excited about this, there are some built-in
things about the language that make forward chaining less nice. For instance:
(f $ \x -> ...) /= (\x -> ... ? f)
(f $ do ...) /= (do ... ? f)
You need to add parentheses for the right sides, which defeats at least part
of the point of ($).
The second is even incompatible in two ways, because left-to-right
impredicative instantiation seems to be back in GHC 7, and so:
runST $ do ...
will work, while
(do ...) ? runST
will be a type error, assuming it's just flip ($) with the usual type.
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