Sometimes I am confused with 'liftA2' and 'converge' functions. 

 

Main difference between those is that:

　　liftA2 takes applicative functor as second and third arguements, for example, array

　　converge takes functions as second and third arguements

// liftA2 :: Applicative m => (a -> b -> c) -> m a -> m b -> m c// converge :: (b -> c -> d) -> (a -> b) -> (a -> c) -> a -> d

 

// liftA2 :: Applicative m => (a -> b -> c) -> m a -> m b -> m c// converge :: (b -> c -> d) -> (a -> b) -> (a -> c) -> a -> dconst { option, curry, liftA2, converge } = require("crocks");const { getState } = require("../../helper");// getColors :: () -> State AppState [String]const getColors = () => getState("colors").map(option([]));// getShapes :: () -> State AppState [String]const getShapes = () => getState("shapes").map(option([]));// buildCard :: String -> String -> Cardconst buildCard = curry((color, shape) => ({  id: `${color}-${shape}`,  color,  shape}));// buildCards :: [String] -> [String] -> [Card]const buildCards = liftA2(buildCard);// generateCards :: () -> State AppState [ Card ]const generateCards = converge(liftA2(buildCards), getColors, getShapes);module.exports = {  generateCards};