Mathematica Programming » Code Structure
Symbols and Expressions
Mathematica has one more basic type than those mentioned before:
In reality, every variable we've used and function we've defined (excluding pure functions) has been a symbol.
One thing to keep in mind is that the only things that can have properties or values in Mathematica are symbols, although a symbol need not have any.
All of the following are symbols:
Automatic AxesLabel $ModuleNumber Rule SetDelayed
In Mathematica, they say everything is an expression. What this means, really, is that outside of the primitive types everything has one common form:
Furthermore, there are tools to parse these structures:
This even applies to things like graphics. Consider the following graphic:
It is, however, still just an expression:
Graphics3D[Sphere, Boxed->False, Lighting->"Neutral", ImageSize->Small ]//FullForm