Haskell Interlude 38: Edwin Brady

[nomeata]

Edwin Brady

Andres and Wouter interview Edwin Brady, most famous for his work on the Idris programming language. We talk about how he got interested in programming with dependent types, his thoughts on dependently typed programming in Haskell, and his vision for Idris

[jaror]

Let me repeat my kbin comment here for more reach:

I think Idris’ bang notation for performing effects in a do-block is pretty, it could look like this:

main = do putStrLn ("You said: " ++ !getLine)

Today, you’d have to come up with a new variable name or figure out the right combinator names:

main = do line <- getLine; putStrLn ("You said: " ++ line)

main = putStrLn . ("You said: " ++) =<< getLine

But unfortunately there are more complicated cases:

main = do print (True || !getLine == "foo")

In a strict language with built-in short-circuiting logical operations the getLine would never be performed, but in Haskell || is just a normal function that happens to be lazy in its second argument. The only reasonable way to implement it seems to be to treat every function as if it was strict and always perform the getLine:

main = do line <- getLine; print (True || line == "foo")

Do you think this is confusing? Or is the bang notation useful enough that you can live with these odd cases? I’m not very happy with this naive desugaring.

[atravers]

Monadic Bang: A plugin for more concise do-block notation, inspired by Idris

I’ve written a GHC plugin that lets you take things like the following code: main :: IO () main = do putStrLn "Which argument would you like to print?" line <- getLine args <- getArgs putStrLn $ args !! read line and instead write this code: main :: IO () main = do putStrLn "Which argument would you like to print?" putStrLn $ !getArgs !! read !getLine This is heavily inspired by Idris’s !-notation, the main difference being that this plugin only allows you to use ! inside of existi…

[jaror]

Thanks for reminding me of that…