Lisp reader

In the programming language Lisp, the reader or  function is the parser which converts the textual form of  Lisp objects to the corresponding internal object structure.

In the original Lisp, S-expressions consisted only of symbols, integers, and the list constructors   and. Later Lisps, culminating in Common Lisp, added literals for floating-point, complex, and rational numbers, strings, and constructors for vectors.

The reader is responsible for parsing list structure, interning symbols, converting numbers to internal form, and calling read macros.

Read table
The reader is controlled by the, which defines the meaning of each character.

Read macros
Unlike most programming languages, Lisp supports parse-time execution of programs, called "read macros" or "reader macros". These are used to extend the syntax either in universal or program-specific ways. For example, the quoted form   operator can be abbreviated as. The  operator can be defined as a read macro which reads the following list and wraps it with. Similarly, the backquote operator (` ) can be defined as a read macro.