A spreadsheet in fewer than 30 lines of JavaScript, no library used

Post by tel » Thu, Nov 14, 2013, 5:13 AM UTC

tel wrote: post #222

tel wrote: post #93

It's not really comparable, but minimalistic spreadsheet applications always remind me of Dan Piponi's Haskell `loeb` function [0]---a "one-line" "spreadsheet" "implementation". The blog post is very interesting to read, but here's the meat. We're looking for a function with type loeb :: Functor f => f (f a -> a) -> f a and without thinking about the meaning of it, we can implement it as loeb x = fmap (\a -> a (loeb…

One more cool trick from the same article (slightly modified). It's a factorial function computed on an "infinite spreadsheet". But how? fact = loeb fact' where fact' 0 _ = 1 fact' n f = n*f (n-1) If we ask GHC for the type of `fact'` then we see that it is Int -> ((Int -> Int) -> Int) which we can interpret via the `Reader Int` monad as being m (m Int -> Int) -- for m a = (Int -> a) Now, `f :: (Int -> a)` as a funct…

    data Stream a = Stream a (Stream a)
                    deriving Functor

    tabulate :: (Int -> a) -> Stream a
    tabulate f = go 0 where
      go n = Stream (f n) (go (succ n))

    index :: Stream a -> (Int -> a)
    index (Stream a _)  0 = a
    index (Stream a st) n = index st (pred n)

    -- btw: tabulate . index == id
    -- and  index . tabulate == id

    fact :: Int -> Int
    fact n = index (loeb facts) n where
      facts :: Stream (Stream Int -> Int)
      facts = tabulate $ \i stream -> i * index stream (i-1)

Post by kamjam » Thu, Nov 14, 2013, 5:41 AM UTC

mattmanser wrote: post #74

dictum wrote: post #62

Earlier quoted context omitted.

And 80% of perceived functionality is what most users — even people who rely on spreadsheets for their work — need. I'm not saying including the other 20% of functionality isn't a good thing to do, but when you're creating a new product or open source project, you can get by (and thrive) building only the 20% of functionality that's used 80% of the time. Why? Because 1% of functionality is still better than 0% (never…

You missed his point. It doesn't actually work well. It doesn't do basic stuff, which makes it entirely unusable. Like you can't move up/down/left/right using the arrow keys. You can't save it. It crashes if you make basic mistakes. The 80% of perceived functionality is that it looks like a spreadsheet app and actually does some basic calculations. It actually does about 5% of what you'd expect even the most basic of…

Post by aboodman » Thu, Nov 14, 2013, 6:11 AM UTC

jcampbell1 wrote: post #190

aufreak3 wrote: post #185

Earlier quoted context omitted.

Doing this all in a webworker might be one way to get security - by sandboxing the with/eval?

Possibly. Web workers are isolated from the DOM, but can still do stuff like import other scripts or do XHR requests, but those would be limited to the same origin. It seems like that would be somewhat XSS safe since you are just passing strings back and forth. I really like this idea. evalSafeAsync(code,context,callback) That being said, for a spreadsheet, you need to bite the bullet and parse the formulas. I don't…

Post by nyan_sandwich » Thu, Nov 14, 2013, 7:32 AM UTC

Post by yurikoval » Thu, Nov 14, 2013, 7:46 AM UTC

st0neage wrote: post #127

=alert("XSS")