hashtable-ref

[procedure] hashtable-ref hashtable key default

R6RS: Returns the value associated to the key in hashtable. If there's no entry for key, default is returned.

See also Concept:HashTable.

Curiously, R6RS makes default argument mandatory, while many other existing implementations make it optional or lack it. See hash-table-ref, hash-table-get, hashtable-get, table-ref for these variations. (IMHO, it is wise for R6RS to choose the name that doesn't conflict those existing names --shiro).