Annotated King Reference Manual/Statements

This page is work in progress.

Simple and Compound Statements

Syntax

sequence_of_statements ::= statement {statement}

statement ::= simple_statement | compound_statement

simple_statement ::=
            null_statement
          | assignment_statement
          | exit_statement
          | procedure_call_statement
          | wait_statement
          | return_statement
          | end_statement

compound_statement ::=
            if_statement
          | case_statement
          | loop_statement
          | declare_statement
          | task_declare_statement
          | select_statement

null_statement ::= null;

statement_identifier ::= direct_name

Rationale

-

Discussion

-

Assignment Statements

Examples

State.Seed <- Seed + 1;

Syntax

assignment_statement ::=  variable_name <- expression;

Rationale

-

Discussion

-

If Statements

Examples

if Success then
   Stick (ID) <- True;
   Stick (Wrap.Next (ID) ) <- True;
   Owner (ID) <- True;
end if;

Syntax

if_statement ::= simple_if_statement | extended_if_statement

simple_if_statement ::=
           if condition then
              sequence_of_statements
          [else
              sequence_of_statements]
           end if;

extended_if_statement ::=
           if condition then
              sequence_of_statements
           else_if condition then
              sequence_of_statements
          {else_if condition then
              sequence_of_statements}
           else
              sequence_of_statements
           end if;

condition ::= boolean_expression

Rationale

-

Discussion

-

Case Statements

Examples

-

Syntax

case_statement ::= normal_case_statement | exception_handling_case_statement

normal_case_statement ::=
          case selecting_expression is
              normal_case_statement_alternative
             {normal_case_statement_alternative}
          end case;

normal_case_statement_alternative ::=
              when discrete_choice_list =>
                 sequence_of_statements

exception_handling_case_statement ::=
          case exception_identifier is
              exception_handling_case_statement_alternative
             {exception_handling_case_statement_alternative}
          end case;

exception_handling_case_statement_alternative ::=
              when exception_occurrence_list =>
                 sequence_of_statements

Rationale

- Normal case statements may appear in any sequence of statements. Exception-handling case statements may only appear in an exception handler.

The exception_identifier must be the identifier following when of the enclosing exception handler.

Discussion

-

Loop Statements

Examples

Get_Line : loop
   exit Get_Line when King.IO.Text.End_Of_Line;

   Value <- Value & King.IO.Text.Next'As_Universal;
Get_Line : end loop;

Syntax

loop_statement ::=
          loop_statement_identifier : [iteration_scheme] loop
             sequence_of_statements
          loop_identifier : end loop;

iteration_scheme ::=
            for loop_parameter_specification
          | for loop_parameter_specification_no_reverse task
          | for iterator_specification [task]

loop_parameter_specification ::=
          defining_identifier in [reverse] discrete_subtype_definition [iterator_filter]

loop_parameter_specification_no_reverse ::=
          defining_identifier in discrete_subtype_definition [iterator_filter]

discrete_subtype_definition ::= discrete_subtype_indication | range_specification

iterator_specification ::=
           defining_identifier of iterable_name [iterator_filter]

iterator_filter ::= when condition

Rationale

-

Discussion

-

Declare Statements

Examples

-

Syntax

declare_statement ::=
          declare_statement_identifier: declare
             declarative_part
          declare_identifier : begin
             sequence_of_statements
          declare_identifier : when identifier =>
             sequence_of_statements
          declare_identifier : end declare;

Rationale

-

Discussion

-

Task Declare Statements

Examples

-

Syntax

task_declare_statement ::=
          task_declare_statement_identifier : task declare
             declarative_part
          task_declare_identifier : begin
             sequence_of_statements
          task_declare_identifier : and
             sequence_of_statements
         {task_declare_identifier : and
             sequence_of_statements}
          task_declare_identifier : end task declare;

Rationale

-

Discussion

-

Exit Statements

Examples

exit Get_Line when King.IO.Text.End_Of_Line;

Syntax

exit_statement ::= exit loop_name [when condition];

Rationale

-

Discussion

-

Wait statements

Examples

wait of 1.0;

Syntax

wait_statement ::= wait wait_mode wait_expression;

wait_mode ::= for | of

Rationale

The wait of statement is for a relative amount of time, and blocks the task for the number of seconds given. It can be read as, "Perform a wait of this many seconds." The wait for statement takes a Duration value and blocks the task until that time arrives, unless it is in the past. It can be read as, "Wait for this time to arrive." The duration is the number of seconds since the epoch, which is not defined, but meaningful values can be constructed using the standard library.

Discussion

-

Select Statements

Examples

-

Syntax

select_statement ::=
          select_statement_identifier : select
             blocking_call
             [sequence_of_statements]
         {select_identifier : or
             blocking_call
             [sequence_of_statements]}
          select_identifier : or
             wait_statement
             [sequence_of_statements]
          select_identifier : end select;

blocking_call ::= assignment_statement | procedure_call_statement

Rationale

A blocking call would be a call to any subprogram of a passive task.

Discussion

-

Procedure Call Statement

Examples

Message_Queue.Put (Item => ID'Image & " waiting for podium");
King.IO.Text.Put_Line (Line => Message);

Syntax

procedure_call_statement ::= procedure_prefix [actual_parameter_part];

actual_parameter_part ::= (parameter_association {, parameter_association})

parameter_association ::= formal_parameter_selector_name => explicit_actual_parameter

explicit_actual_parameter ::= expression | variable_name

Rationale

-

Discussion

-

Return Statement

Examples

return State.Seed;

Syntax

return_statement ::= return [expression] [when condition];

Rationale

-

Discussion

-

End Statement

Examples

end Task_Name;

Syntax

end_statement ::= end task_name;

Rationale

-

Discussion

-