In the programming language Lisp, the reader or read 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 ( xi... ) and (x .
The reader is responsible for parsing list structure, interning symbols, converting numbers to internal form, and calling read macros.
The reader is controlled by the readtable, which defines the meaning of each character.
Similarly, the backquote operator (` ) can be defined as a read macro.