(lexi-lambda.github.io)

398 points declanhaigh | 1 comments | 07 Mar 23 08:47 UTC | HN request time: 0s | source

Show context

bruce343434 ◴[07 Mar 23 10:54 UTC] No.35053912[source]▶

Note that this basically requires your language to have ergonomic support for sum types, immutable "data classes", pattern matching.

The point is to parse the input into a structure which always upholds the predicates you care about so you don't end up continuously defensively programming in ifs and asserts.

replies(12): >>35054046 #>>35054070 #>>35054386 #>>35054514 #>>35054901 #>>35054993 #>>35055124 #>>35055230 #>>35056047 #>>35057866 #>>35058185 #>>35059271 #

jim-jim-jim ◴[07 Mar 23 11:15 UTC] No.35054070[source]▶

>>35053912 #

I think we'll eventually come to regard `if` as we do `goto`.

replies(4): >>35054298 #>>35054351 #>>35054456 #>>35054814 #

raincole ◴[07 Mar 23 12:11 UTC] No.35054456[source]▶

>>35054070 #

I don't know about this. We all have seen this kind of code:

    if(!needToDoTheThing()) return;
    
    DoTheThing();

We could have written it this way:

    if(needToDoTheThing()) {
        DoTheThing();
    }
    else {
        return;
    }

The later is closer to how pattern match looks like. But in my experience, the majority of programmers prefer early return. I regularly see people "refactor" if-else to if-early-return, but I've never seen the opposite.

replies(4): >>35054651 #>>35054833 #>>35065147 #>>35065313 #

1. ParetoOptimal ◴[08 Mar 23 04:38 UTC] No.35065313[source]▶

>>35054456 #

I prefer using early return in monads with guard like:

    safeDiv :: (Monad m, Alternative m) => Int -> Int -> m Int
    safeDiv x y = do
      guard (y /= 0)
      pure (x `div` y)

    main :: IO ()
    main = do
      print $ safeDiv @Maybe 1 0
      print $ safeDiv @[] 1 0
      -- print =<< safeDiv @IO 1 0 -- guard throws an error in IO

Try it out at https://play.haskell.org/saved/a6VsE3uQ

↑

Parse, don't validate (2019)