relation {and relation} | relation {and then relation}
| relation {or relation} | relation {or else relation}
| relation {xor relation}
simple_expression [relational_operator simple_expression]
| simple_expression [not] in range
| simple_expression [not] in subtype_mark
numeric_literal | null | string_literal | aggregate
| name | qualified_expression | allocator | (expression)
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
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)