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Contents
exception EmptyList
datatype 'a lazylist = Nil | Cons of ('a * (unit -> 'a lazylist));
fun next s = let
fun next' Nil = raise EmptyList
| next' (Cons(a,f)) = f()
in
next' s
end ;
fun hd s = let
fun hd' Nil = raise EmptyList
| hd' (Cons(a, _)) = a
in
hd' s
end ;
fun allPrimes n = let
fun isPrime n = let
fun factors n = let
fun factors' 0 acc = acc
| factors' c acc = if (n mod c) = 0
then factors' (c-1) (c :: acc)
else factors' (c-1) acc
in
factors' (n div 2) []
end
in
(List.length (factors n)) = 1
end
fun nextPrime n = let
val nextN = if (n mod 2) = 0 then n + 1 else n + 2
in
if isPrime nextN then nextN else nextPrime nextN
end
in
Cons(n, fn () => (allPrimes (nextPrime n)))
end ;
fun nthPrime n = let
fun nthPrime' 0 s = hd s
| nthPrime' n s = nthPrime' (n-1) (next s)
in
if n <= 0 then raise Domain
else nthPrime' (n-1) (allPrimes 2)
end ;
Version data entries
54 entries across 54 versions & 1 rubygems