junkywunky:
>
> That's the thing. I want to return a list of people who are not overdrawn.
> Something like:
>
> type NI = Int
> type Age = Int
> type Balance = Int
> 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:
>
Right, you mean to write a list filter. List comprehensions are useful
for this:
credit xs = [ p | p@(a,b,c) <- xs, c >= 0 ]
or maybe:
credit xs = filter ok xs
where
ok (a,b,c) = c >= 0
-- Don
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