This is just saying that the type of less is any function that takes two a's as parameters and returns a Bool result. This appears to be a formalization of the Ord (ordered) data type, where less would be used to compare two ordered values and return a Bool result, either True or False. Just a note that the data declaration above is missing a constructor name. It should probably be something like: data Ord a = *Ord* { less :: a -> a -> Bool } Cheers, Darren On Wed, Feb 20, 2013 at 1:18 PM, Emanuel Koczwara <poczta@emanuelkoczwara.pl
wrote:
Hi,
I'm watching Philip Wadler "Faith, Evolution, and Programming Languages" (very cool by the way): http://www.youtube.com/watch?v=8frGknO8rIg
At 00:24:14 there is strange thing on the slide:
data Ord a = { less :: a -> a -> Bool }
It's first time I see function type (and where is definition?) in record syntax. Can somebody explain this?
Emanuel
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