Lisp reader: Difference between revisions

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In the programming language [[Lisp (programming language)|Lisp]], the '''reader''' or '''<code>read</code> 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 [[symbol (programming)|symbol]]s, integers, and the list constructors <code>( <i>''x_i...</i>'' )</code> and <code>(<i>''x</i>'' . <i>''y</i>'')</code>. 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, [[String interning|interning]] symbols, converting numbers to internal form, and calling read macros.

==Read table==

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The reader is controlled by the <code>readtable</code>, which defines the meaning of each [[character (computing)|character]].

==Read macros=={{anchor|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 [[Lisp_Lisp (programming_languageprogramming language)#Self-evaluating_forms_and_quotingevaluating forms and quoting|quoted form]] <code>(quote <i>''x</i>'')</code> operator can be abbreviated as <code>{{'}}''<i>x</i>''</code>. The <code>'</code> operator couldcan be defined as a read macro which reads the following list and wraps it with <code>quote</code>. Similarly, the [[Lisp (programming language)#Backquote|backquote operator]] (` ) can be defined as a read macro.

==NotesReferences==

{{Reflist}}

<references/>

==Bibliography==

* [[John McCarthy (computer scientist)|John McCarthy]] ''et al.'', ''LISP 1.5 Programmer's Manual'', MIT Press, 1962.

* [[David Moon|David A. Moon]], ''MACLISP Reference Manual'', 1974.

* [[Guy Steele]], ''Common LISP: The Language'', Second Edition, 1990.

[[Category:Lisp (programming language)]]

[[Category:ParsersParsing]]

{{programming-stub}}