Fair, but I have been under the impression that the intended use case of Guile is an embedded extension language, like how you describe Lua, and like the language is was intended to replace, Emacs Lisp.

From the website (http://gnu.org/s/guile):

"Guile is an efficient virtual machine that executes a portable instruction set generated by its optimizing compiler, and integrates very easily with C and C++ application code. In addition to Scheme, Guile includes compiler front-ends for ECMAScript and Emacs Lisp (support for Lua is underway), which means your application can be extended in the language (or languages) most appropriate for your user base. And Guile's tools for parsing and compiling are exposed as part of its standard module set, so support for additional languages can be added without writing a single line of C."