Fexl is an interpreter for a programming language based on functions. The interpreter is written in standard C and compiled with strictness and optimization. It is designed to be small, efficient, and suitable for embedded or sandboxed applications. The language has a small grammar and a small implementation. Here is some sample code.
Fexl is an acronym for Function EXpression Language, and it is indeed a language for expressing functions. The name is pronounced Fex'-uhl, somewhat similar to "pixel".
Browse or install the Fexl source code. (Updated Wed 2013-04-10)