Re: [Haskell-beginners] LYAH example

Ahhhh I see, thank you very much for the response! Have a nice day, Sasa { name: Bogicevic Sasa phone: +381606006200 }

On Mar 22, 2017, at 13:30, Francesco Ariis wrote:

On Wed, Mar 22, 2017 at 12:44:23PM +0100, sasa bogicevic wrote:

...

Hi All, Can someone clarify the example I got from LYAH book. This let statement is kinda confusing to me :

applyLog :: (a, String) -> (a -> (b, String)) -> (b, String) applyLog (x, log) f = let (y, newLog) = f x in (y, log ++ newLog)

Hello Sasa, let's rewrite `applyLog`:

applyLog :: (a, String) -> (a -> (b, String)) -> (b, String) applyLog (x, log) f = -- f :: a -> (b, String) let (y, newLog) = f x -- y :: b -- newLog :: String in (y, log ++ newLog) -- (b, String)

f applied to x doesn't produce just `y`, but `y` and `newLog` (in a Tuple). It is perfectly ok to specify a pattern:

let (y, newLog) = f x -- legal

let xyz = f x -- legal too. The first form saves you a `fst`/`snd`

Is it clearer now? _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners