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

ghc hello.hs


` module Main where import System.Environment main :: IO () main = do args <- getArgs num <- getLine putStrLn (“Hello, “ ++ show (foldr1 (+) (map read args))) putStrLn num `