Hi,
I don't understand what's taking place here.
>From Hoogle:
=
liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
Promote a function to a monad, scanning the monadic arguments from left to
right. For example,
liftM2 (+) [0,1] [0,2] = [0,2,1,3]
liftM2 (+) (
On 10-07-23 02:43 PM, michael rice wrote:
liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
[...]
What does it mean to "promote a function to a monad?"
liftM2 f m1 m2 is canned code for
do
a1 <- m1
a2 <- m2
return (f a1 a2)
for example liftM2 f [s,t] [x,y] is [f s x, f s y,
On 11:43 Fri 23 Jul , michael rice wrote:
> Hi,
>
> I don't understand what's taking place here.
>
> >From Hoogle:
>
> =
>
> liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
>
> Promote a function to a monad, scanning the monadic arguments from left to
> right.
On Fri, Jul 23, 2010 at 11:43:08AM -0700, michael rice wrote:
> What does it mean to "promote a function to a monad?"
>
> It would seem that the monad values must understand the function that's being
> promoted, like Ints understand (+).
>
> Prelude Control.Monad> liftM2 (+) (Just 1) (Just 1)
>
El vie, 23-07-2010 a las 15:05 -0400, Nick Bowler escribió:
> On 11:43 Fri 23 Jul , michael rice wrote:
> [...]
> > But how does one add [0,1] and [0,2] to get [0,2,1,3]?
>
> liftM2 (+) [0,1] [0,2] gives the list
>
> [0+0, 0+2, 1+0, 1+2]
which one could have found out by asking ghci:
Prel
ürgen Doser wrote:
From: Jürgen Doser
Subject: Re: [Haskell-cafe] Heavy lift-ing
To: "michael rice"
Cc: haskell-cafe@haskell.org
Date: Friday, July 23, 2010, 4:50 PM
El vie, 23-07-2010 a las 15:05 -0400, Nick Bowler escribió:
> On 11:43 Fri 23 Jul , michael rice wrote:
> [...]
&g
On Jul 23, 2010, at 4:35 PM, michael rice wrote:
Why is it called "lift"-ing?
Basically, because mathematicians like enlightening metaphors. It is
a mathematical term.
A "monadic value" has an "underlying" value. To turn a function that
works on the underlying value into one that work
El vie, 23-07-2010 a las 16:35 -0700, michael rice escribió:
> Thanks all,
>
> Wild, at least up to the "optional" part, which I haven't dug into
> yet.
>
> So the (+) for the Maybe monad and the (+) for the List monad are one
> in the same, the magic springs from the monads.
>
> Why is it calle
Lists are non-deterministic, but the function taken by liftM2 does not
necessarily generate all possible outcomes. In the case of (+) it
does, not in the case of (-):
liftM2 (-) [0,1] [2,3] => [0-1,0-2,1-2,1-3] => [-2,-3,-1,-2]
if all possible cases were generated between the two lists we have to
i
On Fri, Jul 23, 2010 at 09:12:44PM -0500, aditya siram wrote:
> Lists are non-deterministic, but the function taken by liftM2 does not
> necessarily generate all possible outcomes. In the case of (+) it
> does, not in the case of (-):
> liftM2 (-) [0,1] [2,3] => [0-1,0-2,1-2,1-3] => [-2,-3,-1,-2]
>
I wouldn't-it was a bad example. My only point was that because of the
way (>>=) is implemented for lists the order of the arguments 'a' and
'b' in 'liftM2 f a b' matters.
-deech
On Sat, Jul 24, 2010 at 1:37 AM, Lennart Augustsson
wrote:
> Why would you expect swapped operands to (-) ?
>
>
> Sen
On Sat, Jul 24, 2010 at 4:08 PM, aditya siram wrote:
> I wouldn't-it was a bad example. My only point was that because of the
> way (>>=) is implemented for lists the order of the arguments 'a' and
> 'b' in 'liftM2 f a b' matters.
>
> -deech
No, it's not. The type of liftM2 makes this clear:
lif
Perhaps I'm being unclear again. All I was trying to say was that:
liftM2 (-) [0,1] [2,3] /= liftM2 (-) [2,3] [0,1]
-deech
On Sat, Jul 24, 2010 at 9:30 AM, Max Rabkin wrote:
> On Sat, Jul 24, 2010 at 4:08 PM, aditya siram wrote:
>> I wouldn't-it was a bad example. My only point was that because
Prelude Control.Monad> liftM2 (\a b -> a : b : []) "abc" "123"
["a1","a2","a3","b1","b2","b3","c1","c2","c3"]
Prelude Control.Monad>
Got it!
Thanks to all.
Michael
--- On
On 24/07/2010, aditya siram wrote:
> Perhaps I'm being unclear again. All I was trying to say was that:
> liftM2 (-) [0,1] [2,3] /= liftM2 (-) [2,3] [0,1]
>
> -deech
I'm sorry if I'm bumping an old thread, but why should "liftM2 f" be
commutative when "f" isn't?
(I hope I'm not responding incorr
On 17/08/10 17:13, Tilo Wiklund wrote:
On 24/07/2010, aditya siram wrote:
Perhaps I'm being unclear again. All I was trying to say was that:
liftM2 (-) [0,1] [2,3] /= liftM2 (-) [2,3] [0,1]
-deech
I'm sorry if I'm bumping an old thread, but why should "liftM2 f" be
commutative when
> I think the point that was being made is that:
>
> liftM2 (flip f) /= flip (liftM2 f)
>
> This is because the former (well: liftM2 (flip f) a b) effectively does:
>
> do {x <- a; y <- b; return (f y x)}
>
> Whereas the latter (flip (liftM2 f) a b) effectively does:
>
> do {y <- b; x <- a; return
17 matches
Mail list logo
