FmapFunc is just a test module I created with<br><br>instance Functor ((->) r) where ...<br><br> -- ryan<br><br><div class="gmail_quote">On Tue, Aug 31, 2010 at 12:03 PM, michael rice <span dir="ltr"><<a href="mailto:nowgate@yahoo.com">nowgate@yahoo.com</a>></span> wrote:<br>
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Hi, Ryan and all,<br><br>Bingo! I guess my question was all right after all.<br><br>I tried creating an instance earlier but <br><br>*Main> :t (->) Int Char<br><br><interactive>:1:1: parse error on input `->'<br>
<br>What got loaded with FmapFunc? I Hoogled it and got back nothing.<br><br>Michael<br><br>--- On <b>Tue, 8/31/10, Ryan Ingram <i><<a href="mailto:ryani.spam@gmail.com" target="_blank">ryani.spam@gmail.com</a>></i></b> wrote:<br>
<blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br>From: Ryan Ingram <<a href="mailto:ryani.spam@gmail.com" target="_blank">ryani.spam@gmail.com</a>><div class="im">
<br>Subject: Re: [Haskell-cafe] On to applicative<br>To: "michael rice" <<a href="mailto:nowgate@yahoo.com" target="_blank">nowgate@yahoo.com</a>><br></div>Cc: "Vo Minh Thu" <<a href="mailto:noteed@gmail.com" target="_blank">noteed@gmail.com</a>>, <a href="mailto:haskell-cafe@haskell.org" target="_blank">haskell-cafe@haskell.org</a><br>
Date: Tuesday, August 31, 2010, 2:36 PM<div><div></div><div class="h5"><br><br><div>Prelude FmapFunc> let s = show :: ((->) Int) String<br>Prelude
FmapFunc> :t s<br>s :: Int -> String<br>Prelude FmapFunc> let v = fmap ("hello " ++) s<br>Prelude FmapFunc> :t v<br>v :: Int -> String<br>
Prelude FmapFunc> v 1<br>"hello 1"<br><br> -- ryan<br><br><div>On Tue, Aug 31, 2010 at 11:28 AM, michael rice <span dir="ltr"><<a rel="nofollow" href="http://mc/compose?to=nowgate@yahoo.com" target="_blank">nowgate@yahoo.com</a>></span> wrote:<br>
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I'm not sure if my terminology is correct or even if my question makes sense, but I can create "instances" of Maybe, List, IO, and Either.<br><br>Prelude Data.Either> let m = Just 7<br>Prelude Data.Either> :t m<br>
m :: Maybe Integer<br><br>Prelude Data.Either> let l = 2:[]<br>Prelude Data.Either> :t l<br>l :: [Integer]<br><br>Prelude Data.Either> let g = getLine<br>Prelude Data.Either> :t g<br>g :: IO String<br><br>Prelude Data.Either> let e = Right "abc"<br>
Prelude Data.Either> :t e<br>e :: Either a [Char]<br><br>All these instances are functors, each with its own version of fmap that can be applied to it.<br><br>How can I similarly create an instance of (->) so I can apply (->)'s version of fmap<br>
<br>instance Functor ((->) r) where <br> fmap f g = (\x -> f (g x))<br><br>to
it?<div><br><br>Michael<br><br>--- On <b>Tue, 8/31/10, Vo Minh Thu <i><<a rel="nofollow" href="http://mc/compose?to=noteed@gmail.com" target="_blank">noteed@gmail.com</a>></i></b> wrote:<br></div><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;">
<div><br>From: Vo Minh Thu <<a rel="nofollow" href="http://mc/compose?to=noteed@gmail.com" target="_blank">noteed@gmail.com</a>><br>Subject: Re: [Haskell-cafe] On to applicative<br>To: "michael rice" <<a rel="nofollow" href="http://mc/compose?to=nowgate@yahoo.com" target="_blank">nowgate@yahoo.com</a>><br>
Cc: <a rel="nofollow" href="http://mc/compose?to=haskell-cafe@haskell.org" target="_blank">haskell-cafe@haskell.org</a><br></div>Date: Tuesday, August 31, 2010, 1:50 PM<div><div></div><div><br><br><div>2010/8/31 michael rice <<a rel="nofollow" href="http://mc/compose?to=nowgate@yahoo.com" target="_blank">nowgate@yahoo.com</a>><br>
><br>> So it's a type constructor, not a type? Could you please provide a simple example of its usage?<br><br>Sure, although I'm sure you've come by some already.<br><br>-- the identity function<br>id :: a -> a<br>
-- often, we write it like this:<br>-- id x = x<br>-- but here we see the relationship between the ananymous function<br>syntax and the function
type:<br>id = \x -> x<br><br>In fact, if you write in prefix form, it is quite familiar:<br>f :: (->) Int Bool<br>e = Either String Float<br><br>Cheers,<br>Thu<br><br>> Michael<br>><br>> --- On Tue, 8/31/10, Vo Minh Thu <<a rel="nofollow" href="http://mc/compose?to=noteed@gmail.com" target="_blank">noteed@gmail.com</a>> wrote:<br>
><br>> From: Vo Minh Thu <<a rel="nofollow" href="http://mc/compose?to=noteed@gmail.com" target="_blank">noteed@gmail.com</a>><br>> Subject: Re: [Haskell-cafe] On to applicative<br>> To: "michael rice" <<a rel="nofollow" href="http://mc/compose?to=nowgate@yahoo.com" target="_blank">nowgate@yahoo.com</a>><br>
> Cc: <a rel="nofollow" href="http://mc/compose?to=haskell-cafe@haskell.org" target="_blank">haskell-cafe@haskell.org</a><br>> Date: Tuesday, August 31, 2010, 1:17 PM<br>><br>> 2010/8/31 michael rice <<a rel="nofollow" href="http://mc/compose?to=nowgate@yahoo.com" target="_blank">nowgate@yahoo.com</a>><br>
> ><br>> > "Learn You a Haskell ..." says that (->) is a type just like Either. Where can I find its type definition?<br>><br>> You can't define it *in* Haskell as user code. It is a built-in infix<br>
> type constructor (Either or Maybe are type constructors too, not just<br>> types). In fact, if you want to implement a simple, typed functional<br>> language, you'll find it is the only built-in type constructor you<br>
> have to implement (as the implementor of the language).<br>><br>> Also,<br>> Show a => a<br>> is a type too, but you won't find a definition for 'a' or for '=>'.<br>> All those things are defined by the language.<br>
><br>> Cheers,<br>> Thu<br>><br></div></div></div></blockquote></td></tr></tbody></table><br>
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