This is documentation for Mathematica 7, which was
based on an earlier version of the Wolfram Language.
View current documentation (Version 11.2)
Atomic Elements of Expressions
All expressions in Mathematica are ultimately built from a small number of distinct types of atomic elements.
AtomQ test whether an expression is an atom
Head find the head of any expression, including an atom
Symbol the head of a symbol; create a symbol from a name
SymbolName  ▪ Context  ▪ Remove  ▪ Names  ▪ NameQ  ▪ ...
String the head of a string
StringQ  ▪ Characters  ▪ ToCharacterCode  ▪ StringLength  ▪ ToExpression  ▪ ...
Integer  ▪ Real  ▪ Rational  ▪ Complex
NumberQ test for a number of any type