12 Jul
2005
12 Jul
'05
10:52 a.m.
On Tue, 12 Jul 2005, wenduan wrote:
Anyone please tell me what is wrong with the function:
isEmpty ::[a]->Bool isEmpty xs | xs == [] = True |otherwise =False When I tried to load it into the interpreter,it says the following:
Could not deduce (Eq a) from the context () arising from use of `==' at mylab2.hs:16
It means that the comparison with (==) only works for types of the Eq class. This also applies to comparison with the empty list because there are different types of empty lists. Thus you have to write isEmpty :: Eq a => [a] -> Bool But it is a bad solution. Better is isEmpty [] = True isEmpty _ = False or even better: Use the standard function 'null'.