Annotated King Reference Manual/Statements

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This page is work in progress.

Simple and Compound Statements[edit | edit source]

Syntax[edit | edit source]

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
          | raise_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[edit | edit source]

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Discussion[edit | edit source]

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Assignment Statements[edit | edit source]

Examples[edit | edit source]

State.Seed <- Seed + 1;

Syntax[edit | edit source]

assignment_statement ::=  variable_name <- expression;

Rationale[edit | edit source]

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Discussion[edit | edit source]

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If Statements[edit | edit source]

Examples[edit | edit source]

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

Syntax[edit | edit source]

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[edit | edit source]

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Discussion[edit | edit source]

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Case Statements[edit | edit source]

Examples[edit | edit source]

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Syntax[edit | edit source]

case_statement ::=
          case selecting_expression is
              case_statement_alternative
             {case_statement_alternative}
          end case;

case_statement_alternative ::=
              when discrete_choice_list =>
                 sequence_of_statements

Rationale[edit | edit source]

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Discussion[edit | edit source]

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Loop Statements[edit | edit source]

Examples[edit | edit source]

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[edit | edit source]

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[edit | edit source]

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Discussion[edit | edit source]

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Declare Statements[edit | edit source]

Examples[edit | edit source]

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Syntax[edit | edit source]

declare_statement ::=
          declare_statement_identifier: declare
             declarative_part
          declare_identifier : begin
             sequence_of_statements
          declare_identifier : exception
             exception_handler
                {exception_handler}
          declare_identifier : end declare;

Rationale[edit | edit source]

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Discussion[edit | edit source]

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Task Declare Statements[edit | edit source]

Examples[edit | edit source]

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Syntax[edit | edit source]

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[edit | edit source]

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Discussion[edit | edit source]

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Exit Statements[edit | edit source]

Examples[edit | edit source]

exit Get_Line when King.IO.Text.End_Of_Line;

Syntax[edit | edit source]

exit_statement ::= exit loop_name [when condition];

Rationale[edit | edit source]

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Discussion[edit | edit source]

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Wait statements[edit | edit source]

Examples[edit | edit source]

wait of 1.0;

Syntax[edit | edit source]

wait_statement ::= wait wait_mode wait_expression;

wait_mode ::= for | of

Rationale[edit | edit source]

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[edit | edit source]

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Select Statements[edit | edit source]

Examples[edit | edit source]

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Syntax[edit | edit source]

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[edit | edit source]

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

Discussion[edit | edit source]

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Procedure Call Statement[edit | edit source]

Examples[edit | edit source]

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

Syntax[edit | edit source]

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[edit | edit source]

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Discussion[edit | edit source]

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Return Statement[edit | edit source]

Examples[edit | edit source]

return State.Seed;

Syntax[edit | edit source]

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

Rationale[edit | edit source]

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Discussion[edit | edit source]

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Raise Statement[edit | edit source]

Examples[edit | edit source]

raise;

Syntax[edit | edit source]

raise_statement ::= raise [exception_name [with string_expression]] [when condition];

Rationale[edit | edit source]

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Discussion[edit | edit source]

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End Statement[edit | edit source]

Examples[edit | edit source]

end Task_Name;

Syntax[edit | edit source]

end_statement ::= end task_name;

Rationale[edit | edit source]

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Discussion[edit | edit source]

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Exception Handler[edit | edit source]

Examples[edit | edit source]

when Error : others =>
   Message_Queue.Put (Item => ID'Image & " ended by " & Error.Information);
   
-- ...

when others =>
   raise;

Syntax[edit | edit source]

exception_handler ::=
          when [choice_parameter_specification :] exception_choice {| exception_choice} =>
             sequence_of_statements

choice_parameter_specification ::= defining_identifier

exception_choice ::= exception_name | others

Rationale[edit | edit source]

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Discussion[edit | edit source]

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