The KoreLogic Expression Language Library is a C library that
provides a simple expression language that can be embedded in other
programs. This library does not implement a full programming language,
but rather a simpler expression language called KL-EL that is
designed to provide arithmetic and logic operations useful in
situations where embedding a full programming language would be
overkill. KL-EL expressions have access to a full set of arithmetic
and logic operations, and they can access functions and variables
exported from the embedding program. Unlike most other languages
of its kind, KL-EL is statically and strongly typed, which helps
ensure that expressions are valid before they are executed. The
embedding API is designed to be easy to use, and the library itself
is designed to be very small.

WWW: https://sourceforge.net/projects/libklel/