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?