Coming back from a couple weeks off of not reading about them, I find myself mystified once again.
I think they are a way to chain extra data through functions.
And you need them to make basic ghc programs? That sucks.
getArgs gets the command line arguments in a list of strings
getLine takes a string from the program
read converts strings into integers that can be added
foldr1 is a variant on foldr that takes the first element as the first accumulator value
putting stuff on seperate lines in a do block implies »
= is implied by <- notation
Both are bind operations but a little different?
It all kind of does what you think it should from looking at it, but the monadic backend is deeply puzzling (look at the type definitions). I watched a youtube video of Brian something explaining how monads are a natural way of achieving function composition for functions that don’t take in and output the same type, but I can’t really recall how that made so much sense. Monads are slippery
save this is a file hello.hs and run
module Main where
main :: IO ()
main = do
args <- getArgs
num <- getLine
putStrLn ("Hello, " ++ show (foldr1 (+) (map read args)))