[R] how R parses expression?

[xudongyuan]

Hi.All and R developers:
      Since I am a beginner on R,I have some questions when I studied the source code.I wonder if anyone have time to help me?
      My question is how the R expressions change to the c code. That is when I input an expression to the GUI or from a file, how R converts the expression to the parse tree in C code(maybe it is a C function, then what is it?), and then does the sequent processes.
		thanks 
															dongyuan xu