Why do you need this? I don't think you can use this as a scripting language, if that's what you're thinking.
Basically I thought that if I make a function in bash can I invoke it from c?
No, that's not what this is for. This scripting language is meant to control the behavior of the GNU linker, not to perform actual computations.
You can execute whole scripts using system() and such, but that's about it.