Question

the code goes like:

- fun foo(a : int, b :int) =
=   if a > b
=   then []
=   else [a] @ foo(a+1, b)
= ;
val foo = fn : int * int -> int list
- foo(1, 100);
val it = [1,2,3,4,5,6,7,8,9,10,11,12,...] : int list

the function intend to construct a list from a to b, if a is greater or equal than b, otherwise a empty list will be created. when I run the function foo with parameter bound to
1 and 100 for a and b respectively, I got the interesting result:

[1,2,3,4,5,6,7,8,9,10,11,12,...]

what does the … here mean?

Answer 1

It just means that your SML system (SML-NJ, I assume) has omitted part of the output in order to keep the display from becoming overly long. Here it is in a different SML system, Moscow ML:

Moscow ML version 2.01 (January 2004)
Enter `quit();' to quit.
- fun foo(a, b) =
   if a > b
   then []
   else [a] @ foo(a+1, b)
;
> val foo = fn : int * int -> int list
- foo(1, 100);
> val it =
    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,
     22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
     40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57,
     58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75,
     76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93,
     94, 95, 96, 97, 98, 99, 100] : int list
-
- foo(1, 1000);
> val it =
    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,
     22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
     40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57,
     58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75,
     76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93,
     94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109,
     110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124,
     125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139,
     140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154,
     155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169,
     170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184,
     185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199,
     200, ...] : int list
-