Lisp reader
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 . y). 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.
01Read table
The reader is controlled by the readtable, which defines the meaning of each character.
02Read 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 (quote x) operator can be abbreviated as 'x. The ' operator can be defined as a read macro which reads the following list and wraps it with quote. Similarly, the backquote operator (` ) can be defined as a read macro.
Sources and credits
This article is adapted from the Wikipedia article “Lisp reader”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
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