# Ada Programming/Expressions

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## Contents

## Expressions[edit]

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[edit]

expression ::= relation {and relation} | relation {and then relation} | relation {or relation} | relation {or else relation} | relation {xor relation}

relation ::= simple_expression [relational_operator simple_expression] | simple_expression [not] in range | simple_expression [not] in subtype_mark

simple_expression ::= [unary_adding_operator] term {binary_adding_operator term}

term ::= factor {multiplying_operator factor}

factor ::= primary [** primary] | abs primary | not primary

primary ::= numeric_literal | null | string_literal | aggregate | name | qualified_expression | allocator | (expression)

## Name Resolution Rules[edit]

A name used as a primary shall resolve to denote an object or a value.

## Static Semantics[edit]

Each expression has a type; it specifies the computation or retrieval of a value of that type.

## Dynamic Semantics[edit]

The value of a primary that is a name denoting an object is the value of the object.

## Implementation Permissions[edit]

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[edit]

### Examples of primaries[edit]

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[edit]

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. 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).