4.4 Expressions
An
expression is a formula
that defines the computation or retrieval of a value. In this International
Standard, the term “expression” refers to a construct of
the syntactic category
expression
or of any of the other five syntactic categories defined below.
Syntax
Name Resolution Rules
A
name
used as a
primary
shall resolve to denote an object or a value.
Static Semantics
Each expression has a type; it specifies the computation
or retrieval of a value of that type.
Dynamic Semantics
The value of a
primary
that is a
name
denoting an object is the value of the object.
Implementation Permissions
For
the evaluation of a
primary
that is a
name
denoting an object of an unconstrained numeric subtype, if the value
of the object is outside the base range of its type, the implementation
may either raise Constraint_Error or return the value of the object.
Examples
Examples of primaries:
4.0 -- real literal
Pi -- named number
(1 .. 10 => 0) -- array aggregate
Sum -- variable
Integer'Last -- attribute
Sine(X) -- function call
Color'(Blue) -- qualified expression
Real(M*N) -- conversion
(Line_Count + 10) -- parenthesized expression
Examples of expressions:
Volume -- primary
not Destroyed -- factor
2*Line_Count -- term
-4.0 -- simple expression
-4.0 + A -- simple expression
B**2 - 4.0*A*C -- simple expression
R*Sin(θ)*Cos(φ) -- simple expression
Password(1 .. 3) = "Bwv" -- relation
Count in Small_Int -- relation
Count not in Small_Int -- relation
Index = 0 or Item_Hit -- expression
(Cold and Sunny) or Warm -- expression (parentheses are required)
A**(B**C) -- expression (parentheses are required)
Sponsored by Ada-Europe