/// <summary>
/// Parses an assignment or call command
/// </summary>
private ICommandNode ParseAssignmentOrCallCommand()
{
Debugger.Write("Parsing Assignment Command or Call Command");
Position startPosition = CurrentToken.Position;
IdentifierNode identifier = ParseIdentifier();
if (CurrentToken.Type == TokenType.LeftBracket)
{
Debugger.Write("Parsing Call Command");
Accept(TokenType.LeftBracket);
IParameterNode parameter = ParseParameter();
Accept(TokenType.RightBracket);
return(new CallCommandNode(identifier, parameter));
}
else if (CurrentToken.Type == TokenType.Becomes)
{
Debugger.Write("Parsing Assignment Command");
Accept(TokenType.Becomes);
IExpressionNode expression = ParseExpression();
return(new AssignCommandNode(identifier, expression));
}
else
{
return(new ErrorNode(startPosition));
}
}
/**
* C O M M A N D S
*/
/// <summary>
/// Parses a skip command
/// </summary>
/// <returns>An abstract syntax tree representing the skip command</returns>
private ICommandNode ParseSkipCommand()
{
Debugger.Write("Parsing Skip Command");
Position startPosition = CurrentToken.Position;
return(new BlankCommandNode(startPosition));
}
/// <summary>
/// Parses a for command
/// </summary>
private ICommandNode ParseForCommand()
{
Debugger.Write("Parsing For Command");
Position startPosition = CurrentToken.Position;
Accept(TokenType.For);
IdentifierNode identifier = ParseIdentifier();
// Declare I as a new variable of type integer with an undefined value
VarDeclarationNode declaration = new VarDeclarationNode(identifier,
new TypeDenoterNode(
new IdentifierNode(
new Token(TokenType.Identifier, "Integer", startPosition))), startPosition);
// Evaluate E1
Accept(TokenType.Becomes);
IExpressionNode becomesExpression = ParseExpression();
// Assign I to the value of E1
AssignCommandNode assign = new AssignCommandNode(identifier, becomesExpression);
// Evaluate E2
Accept(TokenType.To);
IExpressionNode toExpression = ParseExpression();
Accept(TokenType.Do);
// Execute command
ICommandNode command = ParseSingleCommand();
Accept(TokenType.Next);
return(new ForCommandNode(declaration, assign, toExpression, command, startPosition));
}
/**
* E X P R E S S I O N S
*/
/// <summary>
/// Parses a value parameter
/// </summary>
private IParameterNode ParseValParameter()
{
Debugger.Write("Parsing Value Parameter");
IExpressionNode expression = ParseExpression();
return(new ExpressionParameterNode(expression));
}
/// <summary>
/// Parses a single command
/// </summary>
private ICommandNode ParseSingleCommand()
{
Debugger.Write("Parsing single command");
switch (CurrentToken.Type)
{
case TokenType.Identifier:
return(ParseAssignmentOrCallCommand());
case TokenType.If:
return(ParseIfCommand());
case TokenType.While:
return(ParseWhileCommand());
case TokenType.Let:
return(ParseLetCommand());
case TokenType.Begin:
return(ParseBeginCommand());
case TokenType.For:
return(ParseForCommand());
default:
return(ParseSkipCommand());
}
}
/// <summary>
/// Parses a type denoter
/// </summary>
private TypeDenoterNode ParseTypeDenoter()
{
Debugger.Write("Parsing Type Denoter");
IdentifierNode identifier = ParseIdentifier();
return(new TypeDenoterNode(identifier));
}
/// <summary>
/// Parses an integer expression
/// </summary>
private IExpressionNode ParseIntExpression()
{
Debugger.Write("Parsing Int Expression");
IntegerLiteralNode intLit = ParseIntegerLiteral();
return(new IntegerExpressionNode(intLit));
}
/// <summary>
/// Parses a primary expression
/// </summary>
private IExpressionNode ParsePrimaryExpression()
{
Debugger.Write("Parsing Primary Expression");
switch (CurrentToken.Type)
{
case TokenType.IntLiteral:
return(ParseIntExpression());
case TokenType.CharLiteral:
return(ParseCharExpression());
case TokenType.Identifier:
return(ParseIdExpression());
case TokenType.Operator:
return(ParseUnaryExpression());
case TokenType.LeftBracket:
return(ParseBracketExpression());
default:
Reporter.ReportError($"{CurrentToken.Position} -> Could not parse primary expression");
return(new ErrorNode(CurrentToken.Position));
}
}
/// <summary>
/// Parses a character expression
/// </summary>
private IExpressionNode ParseCharExpression()
{
Debugger.Write("Parsing Char Expression");
CharacterLiteralNode charLit = ParseCharacterLiteral();
return(new CharacterExpressionNode(charLit));
}
/// <summary>
/// Parses a program
/// </summary>
private ProgramNode ParseProgram()
{
Debugger.Write($"Parsing program");
ICommandNode command = ParseCommand();
ProgramNode program = new ProgramNode(command);
return(program);
}
/// <summary>
/// Parses a unary expresion
/// </summary>
private IExpressionNode ParseUnaryExpression()
{
Debugger.Write("Parsing Unary Expression");
OperatorNode operation = ParseOperator();
IExpressionNode expression = ParsePrimaryExpression();
return(new UnaryExpressionNode(operation, expression));
}
/**
* L I T E R A L S
*/
/// <summary>
/// Parses an integer literal
/// </summary>
private IntegerLiteralNode ParseIntegerLiteral()
{
Debugger.Write("Parsing integer literal");
Token integerLiteralToken = CurrentToken;
Accept(TokenType.IntLiteral);
return(new IntegerLiteralNode(integerLiteralToken));
}
/// <summary>
/// Parses a character literal
/// </summary>
private CharacterLiteralNode ParseCharacterLiteral()
{
Debugger.Write("Parsing character literal");
Token characterLiteralToken = CurrentToken;
Accept(TokenType.CharLiteral);
return(new CharacterLiteralNode(characterLiteralToken));
}
/*
* I D E N T I F I E R S
*/
/// <summary>
/// Parses an identifier
/// </summary>
private IdentifierNode ParseIdentifier()
{
Debugger.Write("Parsing Identifier");
Token identifierToken = CurrentToken;
Accept(TokenType.Identifier);
return(new IdentifierNode(identifierToken));
}
/*
* O P E R A T O R S
*/
/// <summary>
/// Parses an operator
/// </summary>
private OperatorNode ParseOperator()
{
Debugger.Write("Parsing operator");
Token OperatorToken = CurrentToken;
Accept(TokenType.Operator);
return(new OperatorNode(OperatorToken));
}
/// <summary>
/// Parses a bracket expression
/// </summary>
private IExpressionNode ParseBracketExpression()
{
Debugger.Write("Parsing Bracket Expression");
Accept(TokenType.LeftBracket);
IExpressionNode expression = ParseExpression();
Accept(TokenType.RightBracket);
return(expression);
}
/// <summary>
/// Parses a begin command
/// </summary>
private ICommandNode ParseBeginCommand()
{
Debugger.Write("Parsing Begin Command");
Accept(TokenType.Begin);
ICommandNode command = ParseCommand();
Accept(TokenType.End);
return(command);
}
/// <summary>
/// Parses a variable parameter
/// </summary>
private IParameterNode ParseVarParameter()
{
Debugger.Write("Parsing Variable Parameter");
Position startPosition = CurrentToken.Position;
Accept(TokenType.Var);
IdentifierNode identifier = ParseIdentifier();
return(new VarParameterNode(identifier, startPosition));
}
/// <summary>
/// Parses a let command
/// </summary>
private ICommandNode ParseLetCommand()
{
Debugger.Write("Parsing Let Command");
Position startPosition = CurrentToken.Position;
Accept(TokenType.Let);
IDeclarationNode declaration = ParseDeclaration();
Accept(TokenType.In);
ICommandNode command = ParseSingleCommand();
return(new LetCommandNode(declaration, command, startPosition));
}
/// <summary>
/// Checks the current token is the expected kind and moves to the next token
/// </summary>
/// <param name="expectedType"></param>
private void Accept(TokenType expectedType)
{
if (CurrentToken.Type == expectedType)
{
Debugger.Write($"Accepted {CurrentToken}");
MoveNext();
}
else
{
Reporter.ReportError($"{CurrentToken.Position} -> " +
$"Incorrect use of token type {CurrentToken.Type}");
}
}
/// <summary>
/// Parses a while command
/// </summary>
private WhileCommandNode ParseWhileCommand()
{
Debugger.Write("Parsing While Command");
Position startPosition = CurrentToken.Position;
Accept(TokenType.While);
IExpressionNode expression = ParseBracketExpression();
Accept(TokenType.Do);
ICommandNode command = ParseSingleCommand();
return(new WhileCommandNode(expression, command, startPosition));
}
/// <summary>
/// Parses a const declaration
/// </summary>
private IDeclarationNode ParseConstDeclaration()
{
Debugger.Write("Parsing Const Declaration");
Position startPosition = CurrentToken.Position;
Accept(TokenType.Const);
IdentifierNode identifier = ParseIdentifier();
Accept(TokenType.Is);
IExpressionNode expression = ParseExpression();
return(new ConstDeclarationNode(identifier, expression, startPosition));
}
/// <summary>
/// Parses a var declaration
/// </summary>
private IDeclarationNode ParseVarDeclaration()
{
Debugger.Write("Parsing Var Declaration");
Position startPosition = CurrentToken.Position;
Accept(TokenType.Var);
IdentifierNode identifier = ParseIdentifier();
Accept(TokenType.Colon);
TypeDenoterNode typeDenoter = ParseTypeDenoter();
return(new VarDeclarationNode(identifier, typeDenoter, startPosition));
}
/// <summary>
/// Parses an expression
/// </summary>
private IExpressionNode ParseExpression()
{
Debugger.Write("Parsing Expression");
IExpressionNode leftExpression = ParsePrimaryExpression();
while (CurrentToken.Type == TokenType.Operator)
{
OperatorNode operation = ParseOperator();
IExpressionNode rightExpression = ParsePrimaryExpression();
leftExpression = new BinaryExpressionNode(leftExpression, operation, rightExpression);
}
return(leftExpression);
}
/// <summary>
/// Parses a single declaration
/// </summary>
private IDeclarationNode ParseSingleDeclaration()
{
Debugger.Write("Parsing Single Declaration");
switch (CurrentToken.Type)
{
case TokenType.Const:
return(ParseConstDeclaration());
case TokenType.Var:
return(ParseVarDeclaration());
default:
Reporter.ReportError($"{CurrentToken.Position} -> Could not parse single declaration");
return(new ErrorNode(CurrentToken.Position));
}
}
/// <summary>
/// Parses a command
/// </summary>
private ICommandNode ParseCommand()
{
Debugger.Write("Parsing command");
List <ICommandNode> commands = new List <ICommandNode>();
commands.Add(ParseSingleCommand());
while (CurrentToken.Type == TokenType.Semicolon)
{
Accept(TokenType.Semicolon);
commands.Add(ParseSingleCommand());
}
if (commands.Count == 1)
{
return(commands[0]);
}
else
{
return(new SequentialCommandNode(commands));
}
}
/// <summary>
/// Parses an if command
/// </summary>
private ICommandNode ParseIfCommand()
{
Debugger.Write("Parsing If Command");
Position startPosition = CurrentToken.Position;
Accept(TokenType.If);
IExpressionNode expression = ParseBracketExpression();
Accept(TokenType.Then);
ICommandNode thenCommand = ParseSingleCommand();
if (CurrentToken.Type == TokenType.Else)
{
Accept(TokenType.Else);
ICommandNode elseCommand = ParseSingleCommand();
Accept(TokenType.EndIf);
return(new IfElseCommandNode(expression, thenCommand, elseCommand, startPosition));
}
Accept(TokenType.EndIf);
return(new IfCommandNode(expression, thenCommand, startPosition));
}
/**
* D E C L A R A T I O N S
*/
/// <summary>
/// Parses a declaration
/// </summary>
private IDeclarationNode ParseDeclaration()
{
Debugger.Write("Parsing Declaration");
List <IDeclarationNode> declarations = new List <IDeclarationNode>();
declarations.Add(ParseSingleDeclaration());
while (CurrentToken.Type == TokenType.Semicolon)
{
Accept(TokenType.Semicolon);
declarations.Add(ParseSingleDeclaration());
}
if (declarations.Count == 1)
{
return(declarations[0]);
}
else
{
return(new SequentialDeclarationNode(declarations));
}
}
/// <summary>
/// Parses ID Expression
/// </summary>
private IExpressionNode ParseIdExpression()
{
Debugger.Write("Parsing Call Expression or Identifier Expression");
Position startPosition = CurrentToken.Position;
IdentifierNode identifier = ParseIdentifier();
if (CurrentToken.Type == TokenType.LeftBracket)
{
// Parse call expression
Debugger.Write("Parsing Call Expression");
Accept(TokenType.LeftBracket);
IParameterNode parameter = ParseParameter();
Accept(TokenType.RightBracket);
return(new CallExpressionNode(identifier, parameter));
}
else
{
Debugger.Write("Parsing Identifier Expression");
return(new IdExpressionNode(identifier));
}
}
/**
* P A R A M E T E R S
*/
/// <summary>
/// Parses a parameter
/// </summary>
private IParameterNode ParseParameter()
{
Debugger.Write("Parsing Parameter");
switch (CurrentToken.Type)
{
case TokenType.Identifier:
case TokenType.IntLiteral:
case TokenType.CharLiteral:
case TokenType.Operator:
case TokenType.LeftBracket:
return(ParseValParameter());
case TokenType.Var:
return(ParseVarParameter());
case TokenType.RightBracket:
return(new BlankParameterNode(CurrentToken.Position));
default:
return(new ErrorNode(CurrentToken.Position));
}
}
