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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
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
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 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)
About DocAda Light:
Preface / Preliminary
/ Help
/ TOC
/ Copyright
DocAda Online at the Ada Home:
Complete RM95
/ Updates
/ News
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