Christian Maeder wrote:
Conal Elliott wrote:
The type argument I ran into trouble with represents a value as a list of increasing lower bounds, ending in the exact value. min produces lower bounds from lower bounds and so is immediately productive before even knowing which argument is the lesser one.
Is this only a matter of efficiency? Can it be compared with a faster equality check that does not need to evaluate terms always, because it compares the internal pointers first (and returns True for equal ones)?
Because min returns one of its arguments, "<=" could be defined in terms of "min" and equality. a <= b = min a b == a "==" would cause further evaluations, but if an equality could look up pointers (to unevaluated thunks) no further evaluation might be necessary, so that min and <= do basically the same.
Cheers Christian
P.S. Maybe it is still a good idea to have a separate user defined class Min for your purpose, because then you don't have to hand-write compare functions, but then I don't know the nesting of your data types, though a generic instance Ord a => Min a may help.