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 -