X - Expression

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. X-expressions are the unification of S-expressions found in the Lisp programming language with XML. X-expressions unify notions of computation with data sharing. The term S-expression or sexp (for symbolic expression) refers to a convention for representing semi-structured data in human-readable textual form. Symbolic expressions are mostly made of symbols and lists. S-expressions are probably best known for their use in the Lisp family of programming languages. Other uses of S-expressions are in Lisp-derived languages such as DSSSL, and as mark-up in communications protocols like IMAP and John McCarthy's CBCL. The details of the syntax and supported data types vary in the different languages, but the most common feature among these languages is the use of S-expressions as parenthesized prefix notation (sometimes known as Cambridge Polish notation).