title: What exactly is the SEXP data type in R's C API and why is it used?
body: <p>I am aware of the wikipedia page on SEXP, and I know that it stands for symbolic expression. I know (vaguely) SEXP is notation to refer to tree data structures in Lisp, but I want to know what motivated the developers to call the data type of R objects in C SEXP. Why SEXP?</p>
  
  <p>I am also confused because if R was made in C and Fortran, why would notation from Lisp be used? Or is SEXP a more general term? Maybe I'm missing something here.</p>