Data.Foldable.foldr1 too strict

Dan Doel dan.doel at
Thu Sep 27 16:32:20 CEST 2012

On Thu, Sep 27, 2012 at 10:09 AM, Brent Yorgey <byorgey at> wrote:
> Isn't that still too strict?  I would expect to see "abcdef" before
> the exception.

No, even foldr1 as hand-written on lists needs to look ahead. Normally
it looks like:

    foldr1 f [x] = x
    foldr1 f (x:xs) = f x (foldr1 xs)

but this is of course sugar for:

    foldr1 f (x:[]) = x
    foldr1 f (x:xs) = f x (foldr1 f xs)

Where it's more obvious that it will hit the bottom before it can
yield the "def".

-- Dan

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