[Haskell-cafe] Accumulator value for "and" and "or"
Twan van Laarhoven
twanvl at gmail.com
Fri Sep 21 06:15:45 EDT 2007
PR Stanley wrote:
> or = foldl (||) False
> and = foldl (&&) True
> I can understand the rationale for the accumulator value - True && 
> where  = True and True ||  where  = False
> Other than the practical convenience is there a reason for having the
> empty list in and and or equating to True and False?
> Thanks, Paul
Another way to think about this is to look at
> any p = or . map p
> all p = and . map p
Now, "all even " should hold, since everything in that list is even.
But not "any even " because there is no even number in the empty list.
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