# SML/NJ Library Manual

#### Synopsis

**functor **`BinaryMapFn`

** (**ORD_KEY**)**** : **ORD_MAP

The BinaryMapFn functor implements applicative maps on an ordered type. The resulting structure will satisfy the interface described in ORD_MAP.

The implementation is based on Stephen Adams' integer set code, which uses binary trees of bounded balance.

#### See Also

ORD_KEY, ORD_MAP, SplayMapFn, ListMapFn, ORD_SET

#### Discussion

Note that inserting a pair into a map that already contains a pair using the same key (in the sense that both keys are considered equal by the comparison function) causes the current pair to be replaced by the new one.

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*Last Modified June 10, 1998*

*Comments to John Reppy*

Copyright © 1998 Bell Labs, Lucent Technologies