source: tools/Grammer/Pl0Grammer.pas

unit Pl0Grammer;

{$mode Delphi}{$H+}

interface

uses
  Classes, SysUtils, UGrammer;

type
  TPl0Grammer = class(TGrammer)
    constructor Create;
  end;

implementation

constructor TPl0Grammer.Create;
begin
  inherited;
  begin
    Rules.Clear;
    with AddRule('Program', rtSequence) do begin
      AddItem('Block', itReference, False, False);
      AddItem('.', itText, False, False);
    end;
    with AddRule('Block', rtSequence) do begin
      AddItem('Declaration', itReference, True, False);
      AddItem('Statement', itReference, False, False);
    end;
    with AddRule('Declaration', rtAlternative) do begin
      AddItem('Constant', itReference, False, False);
      AddItem('Variable', itReference, False, False);
      AddItem('Function', itReference, False, False);
    end;
    with AddRule('Constant', rtSequence) do begin
      AddItem('const', itText, False, False);
      AddItem('ConstantDefinition', itReference, False, False);
      with AddGroup(rtSequence, False, True), Items do begin
        AddItem(',', itText, False, False);
        AddItem('ConstantDefinition', itReference, False, False);
      end;
      AddItem(';', itText, False, False);
    end;
    with AddRule('ConstantDefinition', rtSequence) do begin
      AddItem('Name', itReference, False, False);
      AddItem('=', itText, False, False);
      AddItem('Number', itReference, False, False);
    end;
    with AddRule('Variable', rtSequence) do begin
      AddItem('var', itText, False, False);
      AddItem('Name', itReference, False, False);
      with AddGroup(rtSequence, False, True), Items do begin
        AddItem(',', itText, False, False);
        AddItem('Name', itReference, False, False);
      end;
      AddItem(';', itText, False, False);
    end;
    with AddRule('Function', rtSequence) do begin
      AddItem('Function', itText, False, False);
      AddItem('Name', itReference, False, False);
      AddItem('(', itText, False, False);
      with AddGroup(rtSequence, True, False), Items do begin
        AddItem('Name', itReference, False, False);
        with AddGroup(rtSequence, False, True), Items do begin
          AddItem(',', itText, False, False);
          AddItem('Name', itReference, False, False);
        end;
      end;
      AddItem(')', itText, False, False);
      AddItem('Block', itReference, False, False);
      AddItem(';', itText, False, False);
    end;
    with AddRule('Expression', rtSequence) do begin
      with AddGroup(rtAlternative, True, False), Items do begin
        AddItem('-', itText, False, False);
        AddItem('+', itText, False, False);
      end;
      AddItem('Term', itReference, False, False);
      with AddGroup(rtSequence, False, True), Items do begin
        with AddGroup(rtAlternative, False, False), Items do begin
          AddItem('-', itText, False, False);
          AddItem('+', itText, False, False);
        end;
        AddItem('Term', itReference, False, False);
      end;
    end;
    with AddRule('Term', rtSequence) do begin
      AddItem('Factor', itReference, False, False);
      with AddGroup(rtSequence, False, True), Items do begin
        with AddGroup(rtAlternative, False, False), Items do begin
          AddItem('*', itText, False, False);
          AddItem('/', itText, False, False);
        end;
        AddItem('Factor', itReference, False, False);
      end;
    end;
    with AddRule('Factor', rtAlternative) do begin
      with AddGroup(rtSequence, False, False), Items do begin
        AddItem('Name', itReference, False, False);
        AddItem('(', itText, False, False);
        with AddGroup(rtSequence, True, False), Items do begin
          AddItem('Expression', itReference, False, False);
          with AddGroup(rtSequence, False, True), Items do begin
            AddItem(',', itText, False, False);
            AddItem('Expression', itReference, False, False);
          end;
        end;
        AddItem('(', itText, False, False);
      end;
      AddItem('Number', itReference, False, False);
      AddItem('Name', itReference, False, False);
      with AddGroup(rtSequence, False, False), Items do begin
        AddItem('(', itText, False, False);
        AddItem('Expression', itReference, False, False);
        AddItem(')', itText, False, False);
      end;
    end;
    with AddRule('Statement', rtSequence) do begin
      with AddGroup(rtAlternative, True, False), Items do begin
        with AddGroup(rtSequence, False, False), Items do begin
          AddItem('Name', itReference, False, False);
          AddItem(':=', itText, False, False);
          AddItem('Expression', itReference, False, False);
        end;
        with AddGroup(rtSequence, False, False), Items do begin
          AddItem('begin', itText, False, False);
          AddItem('Statement', itReference, False, False);
          with AddGroup(rtSequence, False, True), Items do begin
            AddItem(',', itText, False, False);
            AddItem('Statement', itReference, False, False);
          end;
          AddItem('end', itText, False, False);
        end;
        with AddGroup(rtSequence, False, False), Items do begin
          AddItem('if', itText, False, False);
          AddItem('Condition', itReference, False, False);
          AddItem('then', itText, False, False);
          AddItem('Statement', itReference, False, False);
        end;
        with AddGroup(rtSequence, False, False), Items do begin
          AddItem('while', itText, False, False);
          AddItem('Condition', itReference, False, False);
          AddItem('do', itText, False, False);
          AddItem('Statement', itReference, False, False);
        end;
        with AddGroup(rtSequence, False, False), Items do begin
          AddItem('return', itText, False, False);
          AddItem('Expression', itReference, False, False);
        end;
        with AddGroup(rtSequence, False, False), Items do begin
          AddItem('write', itText, False, False);
          AddItem('Expression', itReference, False, False);
        end;
      end;
    end;
    with AddRule('Condition', rtAlternative) do begin
      with AddGroup(rtSequence, False, False), Items do begin
        AddItem('odd', itText, False, False);
        AddItem('Expression', itReference, False, False);
      end;
      with AddGroup(rtSequence, False, False), Items do begin
        AddItem('Expression', itReference, False, False);
        with AddGroup(rtAlternative, False, False), Items do begin
          AddItem('=', itText, False, False);
          AddItem('<>', itText, False, False);
          AddItem('<', itText, False, False);
          AddItem('<=', itText, False, False);
          AddItem('>', itText, False, False);
          AddItem('=>', itText, False, False);
        end;
        AddItem('Expression', itReference, False, False);
      end;
    end;

(*  http://www.felix-colibri.com/papers/compilers/pl0_grammar/pl0_grammar.html

    program = block '.' .
    block =  { declaration } statement .
    declaration = constant | variable | function .
      constant = CONST constant_definition { ',' constant_definition } ';' .
        constant_definition = NAME '=' NUMBER .
      variable = VAR NAME { ',' NAME } ';' .
      function = FUNCTION NAME '(' [ NAME { ',' NAME } ]  ')' block ';' .
        expression = [ ( '-' | '+' ) ] term { ( '-' | '+' ) term } .
          term = factor { ( '*' | '/' ) factor } .
            factor = NAME '(' [ expression { ',' expression } ] ')'
             | NUMBER | NAME | '(' expression ')' .
        statement = [ NAME ':=' expression
             | BEGIN statement { ';' statement } END
             | IF condition THEN statement
             | WHILE condition DO statement
             | RETURN expression
             | WRITE expression ] .
          condition = ODD expression
             | expression ( '=' | '<>' | '<' | '<=' | '>' | '>=' ) expression .
             *)
  end;
end;


end.