6 ms·

I noticed that your blog post differed from the actual code in your git repository. In the blog post, you defined `shift` to be: shift v = pad (map Jus

I noticed that your blog post differed from the actual code in your git repository. In the blog post, you defined `shift` to be: shift v = pad (map Just (concatMap add (group (catMaybes v))))) Nothing (length v) whereas the code gives: shift v = take n (v' <> empty n) where n = length v v' = group (filter isJust v) >>= go go (Just a : Just b : ts) = Just (a + b) : go ts go ts = ts From my understanding of the blog post's logic, the former doesn't handle the case where `v = replicate 4 (Just 2)`, since it returns `[Just 4, Just 2, Just 2, Nothing]`. Am I correct, and if so, why does the latter version fix this problem? For reference, I know little to no Haskell.

taylorfausak 12y ago
Wow, excellent catch! I apologize for the discrepancy. I must have made a mistake simplifying the game code for the blog post. I created a Gist [1] to showcase the differences. The problem in the blog post is the `add` function. It should recurse (like `go` in the Hs2048 package). I fixed the post [2] with this line: add (x : y : rest) = x + y : add rest [1]: https://gist.github.com/tfausak/4401ef0b43b5c1db0570 https://gist.github.com/tfausak/4401ef0b43b5c1db0570 [2]: https://github.com/tfausak/tfausak.github.io/issues/31 https://github.com/tfausak/tfausak.github.io/issues/31
- jabagawee 12y ago
  Oh! So `go` is a function that's defined within `shift`. That's the crucial part I was missing. Why is it named "go"? EDIT: While I have your attention, do you mind also pointing me to some resources to learn about this ">>=" operator? I recall it's something related to monads...
  - taylorfausak 12y ago
    As ibotty said, I named the anonymous inner worker function `go`. From what I can tell, it seems to be pretty common in Haskell. As for `>>=` (also known as `bind`), I'm using it as a more generic version of `concatMap`. The following expressions are basically the same: concat (map (\ x -> [x, -x]) [1, 2, 3]) concatMap (\ x -> [x, -x]) [1, 2, 3] [1, 2, 3] >>= \ x -> [x, -x] If you want to learn more, check out LYAH [1]. [1]: http://learnyouahaskell.com/a-fistful-of-monads http://learnyouahaskell.com/a-fistful-of-monads
  - gu 12y ago
    The bind operator (>>=) is commonly expressed in 'do' notation. The following two code snippets are equivalent: do x <- foo; y <- bar; baz x y foo >>= \x -> bar >>= \y -> baz x y
  - ibotty 12y ago
    `go` is a very old name for worker functions in haskell. i have been told it originates in glasgow (where ghc was first developed).

taylorfausak 12y ago

Wow, excellent catch! I apologize for the discrepancy. I must have made a mistake simplifying the game code for the blog post. I created a Gist [1] to showcase the differences. The problem in the blog post is the `add` function. It should recurse (like `go` in the Hs2048 package). I fixed the post [2] with this line: add (x : y : rest) = x + y : add rest [1]: https://gist.github.com/tfausak/4401ef0b43b5c1db0570 https://gist.github.com/tfausak/4401ef0b43b5c1db0570 [2]: https://github.com/tfausak/tfausak.github.io/issues/31 https://github.com/tfausak/tfausak.github.io/issues/31

jabagawee 12y ago
Oh! So `go` is a function that's defined within `shift`. That's the crucial part I was missing. Why is it named "go"? EDIT: While I have your attention, do you mind also pointing me to some resources to learn about this ">>=" operator? I recall it's something related to monads...
- taylorfausak 12y ago
  As ibotty said, I named the anonymous inner worker function `go`. From what I can tell, it seems to be pretty common in Haskell. As for `>>=` (also known as `bind`), I'm using it as a more generic version of `concatMap`. The following expressions are basically the same: concat (map (\ x -> [x, -x]) [1, 2, 3]) concatMap (\ x -> [x, -x]) [1, 2, 3] [1, 2, 3] >>= \ x -> [x, -x] If you want to learn more, check out LYAH [1]. [1]: http://learnyouahaskell.com/a-fistful-of-monads http://learnyouahaskell.com/a-fistful-of-monads
- gu 12y ago
  The bind operator (>>=) is commonly expressed in 'do' notation. The following two code snippets are equivalent: do x <- foo; y <- bar; baz x y foo >>= \x -> bar >>= \y -> baz x y
- ibotty 12y ago
  `go` is a very old name for worker functions in haskell. i have been told it originates in glasgow (where ghc was first developed).