Simple addition to Control.Arrow
I keep finding myself needing to apply functions to both elements in a tuple and now that I've started playing around with AFRP libraries I find myself applying arrows to both sides of tuples there too. As a result I would like to propose the following addition to Control.Arrow: both :: Arrow a => a b c -> a (b, b) (c, c) both = join (***) -- or if importing join from Control.Monad is undesirable both f = f *** f Why not just write "f *** f" I hear you ask? Because when f is not a trivial expression then you need to either bind it to a new name and use "newName *** newName" (which I personally dislike, because I'm terrible at coming up with names) or write "join (***) f" which I don't find a particularly appealing notation either. Kind regards, Merijn Verstraaten
I don't know what is the best name for it, but I have found myself defining
this function lot of times.
On Wed, Oct 10, 2012 at 7:15 AM, Merijn Verstraaten
I keep finding myself needing to apply functions to both elements in a tuple and now that I've started playing around with AFRP libraries I find myself applying arrows to both sides of tuples there too. As a result I would like to propose the following addition to Control.Arrow:
both :: Arrow a => a b c -> a (b, b) (c, c) both = join (***) -- or if importing join from Control.Monad is undesirable both f = f *** f
Why not just write "f *** f" I hear you ask? Because when f is not a trivial expression then you need to either bind it to a new name and use "newName *** newName" (which I personally dislike, because I'm terrible at coming up with names) or write "join (***) f" which I don't find a particularly appealing notation either.
Kind regards, Merijn Verstraaten
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Should perhaps be noted that this exists in the lens package as "over both"
and also for up to 9-tuples as "over each".
On Tue, Jan 8, 2013 at 3:21 AM, Daniel Díaz Casanueva wrote: I don't know what is the best name for it, but I have found myself
defining this function lot of times. On Wed, Oct 10, 2012 at 7:15 AM, Merijn Verstraaten <
merijn@inconsistent.nl> wrote: I keep finding myself needing to apply functions to both elements in a
tuple and now that I've started playing around with AFRP libraries I find
myself applying arrows to both sides of tuples there too. As a result I
would like to propose the following addition to Control.Arrow: both :: Arrow a => a b c -> a (b, b) (c, c)
both = join (***)
-- or if importing join from Control.Monad is undesirable
both f = f *** f Why not just write "f *** f" I hear you ask? Because when f is not a
trivial expression then you need to either bind it to a new name and use
"newName *** newName" (which I personally dislike, because I'm terrible at
coming up with names) or write "join (***) f" which I don't find a
particularly appealing notation either. Kind regards,
Merijn Verstraaten _______________________________________________
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participants (3)
-
dag.odenhall＠gmail.com -
Daniel Díaz Casanueva -
Merijn Verstraaten