How to return an array with each element responding to a certain check

Question

I would like to return a list of Bools where each responds to a certain check, here is a javascript example:

if(x == 2)
    a = false;
if(x == 3)
    b = false;
if(y == 2)
    c = false;
if(y == 3)
    d = false;

return [a, b, c, d];

Dirty example, I know. Just wondering what a good approach might be.

You could find answer for your question here. [Return multiple values in JavaScript](http://stackoverflow.com/a/2917186/6442115) — Rama krishna, Nov 05 '16 at 17:11
Where exactly are the checks coming from? This is too broad to recommend anything in particular except the code for your exact example that epsilonhalbe provides. — chepner, Nov 05 '16 at 17:12

score 1 · Answer 1 · answered Nov 05 '16 at 17:38

1

x=5
y=3

elementary

zipWith (==) [x,x,y,y] [2,3,2,3]
[False,False,False,True]

or with magic

import Control.Monad (liftM2)
liftM2 (==) [x,y] [2,3]
[False,False,False,True]

answered Nov 05 '16 at 17:38

karakfa

score 0 · Answer 2 · answered Nov 05 '16 at 17:31

you can always use

f :: (Eq a, Num a,Eq b, Num b) => a -> b -> [Bool]
f x y = [x == 2, x == 3, y == 2, y == 3]

if you have only one parameter and multiple predicates you can do something like

f x = map ($ x) [p1,p2,p3,p4]
 where p1 = odd
       p2 = even
       p3 = (==3)
       p4 = (==4)

which lends itself good to creating the checks programmatically another trick is to use it the other way around

f x = map (==x) [1..10]

or when you have a list of xs you can use zipWith (==) xs [1..].

2 Answers2