On Tue, May 19, 2009 at 7:07 AM, michael rice
A little further along in "The Little MLer" the ints function is replaced by other functions like primes and fibs, which also return Links:
fun primes(n) = if is_prime(n+1) then Link(n+1,primes) else primes(n+1)
fun fibs(n)(m) = Link(n+m,fibs(m))
which are passed to chain_item:
fun chain_item(n,Link(i,f)) = if eq_int(n,1) then i else chain_item(n-1,f(i))
which can be called to request the nth (12th) prime number beginning at 1.
- chain_item(12,primes(1)); GC #0.0.0.1.3.61: (1 ms) val it = 37 : int -
So I guess the answer to your question about whether the function is ever called with a different value may be, yes.
Actually, it's not calling it with another value; notice that chain_item calls f(i), with i coming directly from the chain. Consider this alternate definition: (I'm not sure the syntax is exactly right, but you get the idea) datatype chain = Link of (int * ( unit -> chain )) fun intsFrom(n) = fun unit => (n, intsFrom (n+1)) fun ints(n) = intsFrom n () Now you *can't* call the function embedded in the link with another value. fun chain_item(n,Link(i,f)) = if eq_int(n,1) then i else chain_item(n-1,f unit) And this type for "chain" is almost the same as [Int] in Haskell, due to laziness. -- ryan