Join two IOs with - in haskell
haskell concat two string
haskell int to string
haskell append int to string
I need to join two
IO Strings with a
- in between. Here's what I came up with, which works - what's the right way?
import System.Environment f :: String -> String -> IO String f x y = (foldl1 (++)) <$> sequence [(getEnv x),(return "-"),(getEnv y)]
You could here use an applicative style function:
f :: String -> String -> IO String f x y = withHyp <$> getEnv x <*> getEnv y where withHyp ex ey = ex ++ '-' : ey
So here we join the two
Strings that are then joined with a hypen in the middle through the
Or for a list of environment variables that we need to fetch, we can use
mapM and perform an
import Data.List(intercalate) f :: [String] -> IO String f xs = intercalate "-" <$> mapM getEnv xs
How to combine two strings i Haskell and return a new string, combine = zipWith (++). zipWith takes two lists, and applies the function given to the first item of both lists, then the second, etc. If one list is longer than the other, Actions are inert until run. Only one IO action in a Haskell program is run (main). Do-blocks combine multiple actions together into a single action. Combined IO actions are executed sequentially with observable side-effects. Arrows are used to bind action results in a do-block. Return is a function that builds actions. It is not a form of
I'll be honest, the idea behind your approach actually looks pretty sane to me. To start with, I'd probably use
concat intsead of
foldl1 (++), and drop some parens, getting us to:
f x y = concat <$> sequence [getEnv x, return "-", getEnv y]
This really doesn't seem that bad to me. But if I really wanted to push farther, here's some thoughts I would have. First, I'd recall the
f x y = intercalate "-" <$> sequence [getEnv x, getEnv y]
There's a handy shorthand for applying a function to each element of a list, too;
mapM f = sequence . map f. So:
f x y = intercalate "-" <$> mapM getEnv [x,y]
I would stop there; it looks quite clean and maintainable to me.
Merging streams of IO actions? : haskell, When you have multiple producers and want to consume them in a single consumer you usually do Haskell Game Enpuzzled Released for Android and iOS. haskell documentation: Merge Sort. Example. Ordered merging of two ordered lists. Preserving the duplicates: merge :: Ord a => [a] -> [a] -> [a] merge xs  = xs
One way of joining two
IO Strings would be:
dash :: IO String -> IO String -> IO String dash x y = do s1 <- x s2 <- y return $ s1 <> "-" <> s2
We "unbox" each of
y to get the contained
Strings, then "rebox` them with a hyphen (using the analogy for Functors).
It can be shortened to:
dash = liftA2 (\s1 s2 -> s1 <> "-" <> s2)
liftA2 :: Applicative f => (a -> b -> c) -> f a -> f b -> f c takes a binary function and "lifts" it into a binary function on
Applicatives, which are a superset of
f can then be implemented as
f x y = dash (getEnv x) (getEnv y).
IPhone, cd ~/.mobile-haskell $ curl -o ghc-aarch64-apple-ios.tar.xz our project and adding a New Group ,. 2. Add Source Folder for Haskell Code You can either set this up in the story board and connect it via an IBOutlet . First go There are at least two ways to use Haskell to make iPhone apps. One is having a Haskell-to-iPhone compiler, which would probably cross-compile from another host environment (probably Mac OS X). Another way is to write Haskell programs that generate iPhone-compatible code when run (rather than when compiled), based on an embedded DSL, similarly
Mobile Haskell (iOS), One or two short stretches of sand prevented the cup from overflowing, but A game of baseball was first on the tapis, the ladies joining. 25s.; G. S. Haskell, ih. 3m. ios.: M. J. Andrews, ih. 8m.; S. H. Farnham, ih. Sm. 5s.; G. P. Washburn, ih. Converts an association list to a string. The string will have one pair per line, with the key and value both represented as a Haskell string. This function is designed to work with [(String, String)] association lists, but may work with other types as well.
The Wheel and Cycling Trade Review, Reg. of Deeds, lxxiii, IoS, 150. Joseph Cutler's company of volunteers and marched to join General Gates at the Northward, service twenty-four days. Insert an element into the middle of a list. Generally, you will have to split the list into two smaller lists, put the new element to in the middle, and then join everything back together.
Soldiers of Oakham, Massachusetts, in the revolutionary war, the , Studying a pure functional programming, such as Haskell, can be an eye-opening experience. The standard library in Haskell provides a zip In Haskell, lists are what Arrays are in most other languages. Creating simple lists. splitting a list into two parts splitAt: splitAt 3 "foo bar baz"-->
- Are you sure that works the way you want? Looks essentially equivalent to
f x y = getEnv x(up to some nonsense with yours throwing extra exceptions, perhaps) to me.
- no it doesn't. fixed.
- even uglier now!
- Just a note for OP about
foldl1 (++)for a 3 item list is evaluated as
(a ++ b) ++ c, which is slightly slower than
a ++ (b ++ c)due to traversing
concatis actually implemented as something more like
foldr (++) (give or take some differences in syntax)
- change signature to match
String -> String -> IO Stringplease