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(* Disclaimer:  This code is not documented. *)

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(* LEN (Length)  Note that it is polymorphic *)

fun len [] = 0
  | len (head::tail) = 1 + len tail;

(* --- Example Applications --------------------------------

len [1,2,3];
len ["CSC", "324", "is", "fun"];

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(* FIB (Fibonacci) *)

fun fib 0 = 0
  | fib 1 = 1
  | fib n = fib(n-1) + fib(n-2);

(* --- Example Applications --------------------------------

fib 0;

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(* LISTSUM1, LISTSUM2 Sums a list of integers - several alternatives *)

fun listsum1 L = if (null L) then 0 else (hd L) + listsum1 (tl L);

(* OR *)

fun listsum2 [] = 0
  | listsum2 (h::t) = h + listsum2 t;

(* --- Example Applications --------------------------------

listsum [1,2,3];

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(* REVERSE - Look at this! How to fix the problem? *)

fun reverse (h::t) = reverse(t) @ [h];


(* --- Example Applications --------------------------------

reverse [1,2,3];

reverse ["I", "am", "hungry"];

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(*  EVEN - mutual recursion example *)

(* The following doesn't work:
fun even 0 = true
  | even x = odd (x-1);  - can't type: odd not defined

BUT this does.  Note the multiple recursion *)

fun even 0 = true
  | even x = odd (x-1)
and odd 0 = false
  | odd x = even (x-1);

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