Re: inits

On 2006-04-08, Tim Toorop wrote:

Josef Svenningsson wrote:

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On 4/8/06, Tim Toorop wrote:

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On the other hand, I think the new spiffy inits is quite clear once you notice why its map (const xn) $ undefined:xn

I think it would be even clearer if it were defined like this:

...

inits xs = zipWith take [0..] $ map (const xs) xs

That way you don't have this ugly special case for the first element in the list. But there is an even better advantage: it is strict again! So it's termination properties are exactly like the Prelude one. This version *can* be used as a drop-in replacement of the Prelude version.

Cheers,

/Josef

Yes it is very clear ... except for the fact that it doesn't work correctly. It misses the last element. now we could write inits2' xn = (zipWith take [0..] $ map (const xn) xn ) ++ [xn] Though I dont know if this really is clearer, and it seems to make the garbage collector work slightly more And which I think does exactly the same as inits' xn@(_:_) = zipWith take [0..] $ map (const xn) $ undefined:xn

Yes, but is there any real need to use the ugly pattern syntax? Surely inits xs = zipWith take [0..] $ map (const xs) (undefined:xs) (I still think letting head $ inits undefined be [] rather than undefined is better than the current def.) -- Aaron Denney -><-