What is the haskell way to do this?
for (int i = 0 ; i < 1000 ; i++)
for (int j = 0 ; j < 1000 ; j++)
ret = foo(i , j ) #I need the return value.
More background: I am solving euler problem 27 , and I have got:
value a b =
let l = length $ takeWhile (isPrime) $ map (\n->n^2 + a * n + b) [0..]
in (l, a ,b)
The next step is to get a list of tuple by looping through all the possible a and b and then do the following processing:
foldl (\(max,v) (n,a,b)-> if n > max then (n , a * b) else (max ,v) ) (0,0) tuple_list
but I have no idea how to loop through two variables ..Thanks.
Use a nested list comprehension. Here 'foo' is '(,)'':
[ (i,j) | i <- [0 .. 999], j <- [0 .. 999] ]
Or laid out to make the nesting clearer:
[ foo i j
| i <- [0 .. 999]
, j <- [0 .. 999]
]
As well as dons' answer, you can use the list monad:
do
i <- [0 .. 999]
j <- [0 .. 999]
return (foo i j)
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