8.3 Expressions
An expression is a construct that returns a value, such as a variable reference, literal, procedure call, or conditional.
[16] expression = primitive-expression | derived-expression
Expression types are categorized as primitive or derived. Primitive expression types include variables and procedure calls. Derived expression types are not semantically primitive but can instead be explained in terms of the primitive constructs. They are redundant in the strict sense of the word, but they capture common patterns of usage, and are, therefore, provided as convenient abbreviations.