27 May
2007
27 May
'07
9:17 a.m.
type Person = (NI, Age, Balance) type Bank = [Person]
credit :: Bank -> [Person] credit [(a,b,c)] = [(a,b,c)] if c >= 0 then [(a,b,c)] else error "overdrawn customer"
except this doesn't work with things like:
credit [(1,2,3),(4,5,6)]
Hi, that's because Haskell syntax is made for brains with high modality. When you declare a type, writing a type signature in square brackets make it to be a list of arbitrary number of elements of the inner type; when you write a pattern, one with an element in square brackets matches a single-element list. What you want is to credit abcs = filter (\(a,b,c) -> c>=0) abcs And if you think it looks like a machine-level assembly language, then you are probably right. David