This package provides an intuitive functional programming interface for LaTeX2, which is an alternative choice to expl3 or LuaTeX, if you want to do programming in LaTeX. Although there are functions in LaTeX3 programming layer (expl3), the evaluation of them is from outside to inside. With this package, the evaluation of functions is from inside to outside, which is the same as other programming languages such as Lua. In this way, it is rather easy to debug code too.