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using AtLangCompiler.Methods;
using System.Reflection;
namespace AtLangCompiler;
internal class Parser
{
private readonly Lexer lexer;
private readonly IReadOnlyDictionary<TokenType, IStatementParser> statementParsers;
internal Token current;
internal string varName = string.Empty;
public Parser(Lexer lexer)
{
this.lexer = lexer;
this.statementParsers = Assembly.GetExecutingAssembly()
.GetTypes()
.Where(t => t.CustomAttributes.Any(e => e.AttributeType == typeof(ParserForAttribute)))
.SelectMany(t => t.GetCustomAttributes<ParserForAttribute>().Select(attr => new
{
attr.TokenType,
ParserType = t
}))
.ToDictionary(
entry => entry.TokenType,
entry => (IStatementParser)Activator.CreateInstance(entry.ParserType)!
);
this.current = this.lexer.NextToken();
}
internal void Eat(TokenType type)
{
if (current.Type == type)
{
current = lexer.NextToken();
}
else
{
throw new Exception($"Expected {type}, got {current.Type}");
}
}
internal IList<ASTNode> ParseProgram()
{
IList<ASTNode> stmts = new List<ASTNode>();
while (current.Type != TokenType.EOF)
{
ASTNode? stmt = ParseStatement();
if (stmt != null) stmts.Add(stmt);
}
return stmts;
}
internal ASTNode? ParseStatement()
{
if (current.Type == TokenType.AT)
{
Eat(TokenType.AT);
if (current.Type == TokenType.IDENT)
{
varName = current.Text;
Eat(TokenType.IDENT);
Eat(TokenType.EQUAL);
if (statementParsers.TryGetValue(current.Type, out var statementParserIdent))
{
return statementParserIdent.ParseStatement(this);
}
throw new Exception("Invalid assignment");
}
if (statementParsers.TryGetValue(current.Type, out var statementParserAt))
{
return statementParserAt.ParseStatement(this);
}
throw new Exception("Unexpected after '@'");
}
if (statementParsers.TryGetValue(current.Type, out var statementParser))
{
return statementParser.ParseStatement(this);
}
if (current.Type == TokenType.EOF)
{
return null;
}
else
{
throw new Exception($"Unexpected token {current.Type} in statement");
}
}
internal ASTNode ParseExpression()
{
ASTNode left = ParseSimpleExpr();
while (current.Type == TokenType.PLUS)
{
string op = current.Text;
Eat(TokenType.PLUS);
ASTNode right = ParseSimpleExpr();
left = new BinaryExpression(left, op, right);
}
return left;
}
private ASTNode ParseSimpleExpr()
{
if (current.Type == TokenType.AT)
{
Eat(TokenType.AT);
string name = current.Text;
Eat(TokenType.IDENT);
return new VarReference(name);
}
else if (current.Type == TokenType.STRING)
{
string val = current.Text;
Eat(TokenType.STRING);
return new StringLiteral(val);
}
else
{
throw new Exception($"Unexpected token {current.Type} in expression");
}
}
}
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