sml-examples/basics/built-in-data-structures/hashtable.sml

(* 1: Narrow down the type of the hashtable by adding a type contraint.
 * 2: Call `HashTable.mkTable` with 2 arguments:
 * 2.1: A hash function `HashString.hashString` and
 * 2.2: an equality function `op=`.
 * 3: Call the resulting function with 2 arguments:
 * 3.1: an initial size of the hash table and
 * 3.2: an exception to be thrown, when a key cannot be found in the hashtable and returning Option is not appropriate.
 *)
val ht : (string, int) HashTable.hash_table =
    HashTable.mkTable (HashString.hashString, op=) (42, Fail "not found");

HashTable.insert ht ("a", 1);
HashTable.insert ht ("b", 2);
HashTable.find ht "c";          (* -> Option *)
HashTable.remove ht "c";        (* -> Exception *)