Hi David, On 2018-08-31 04:09, David Feuer wrote:
What about functions like length? length (repeat ()) is bottom. repeat () is not bottom. Ergo, length is partial.
This caught me by surprise - I would have never considered 'length' to be a partial function! Maybe I don't quite understand what it means for some expression to be 'bottom' (I thought that's the same as 'undefined'). My naive understanding was that a partial function is one which has no definition for certain arguments; in particular, it has no definition which could be used while doing equational reasoning by hand, on a piece of paper (i.e. without running the program). It appears that this is not quite correct -- instead, any function which fails to return anything (at runtime!) for certain arguments is partial? E.g. 'sort' would be partial or even 'elem' (consider 'True `elem` repeat False')? -- Frerich Raabe - raabe@froglogic.com www.froglogic.com - Multi-Platform GUI Testing