The Evolution of Language

Descartes:

2x

Church:

 λx.2x

McCarthy:

(LAMBDA (X) (* 2 X))

W3C:

<?xml version="1.0"?>
<LAMBDA­TERM>
   <VAR­LIST>
      <VAR> X </VAR>
   </VAR­LIST>
   <EXPR>
      <APPLICATION>
          <EXPR> <CONST> * </CONST> </EXPR>
          <ARGUMENT­LIST>
             <EXPR> <CONST> 2 </CONST> </EXPR>
             <EXPR> <VAR> X </VAR> </EXPR>
          </ARGUMENT­LIST>
      </APPLICATION>
   </EXPR>
</LAMBDA­TERM>