feat(core/asm): add assembler parser
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dualfroz committed
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using System;
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using System.Collections.Generic;
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namespace Chip8.Core.Assembly;
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public sealed class Parser
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{
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static readonly HashSet<string> directives = new(StringComparer.OrdinalIgnoreCase)
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{
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"DB", "DW", "ORG", "ALIGN",
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};
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readonly List<Token> tokens;
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int index;
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public Parser(List<Token> tokens)
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{
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this.tokens = tokens;
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}
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public List<Statement> parse()
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{
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var statements = new List<Statement>();
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while (current().kind != TokenKind.EndOfFile)
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{
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if (current().kind == TokenKind.EndOfLine)
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{
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index++;
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continue;
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}
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parseLine(statements);
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}
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return statements;
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}
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void parseLine(List<Statement> statements)
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{
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List<Token> line = takeLine();
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int cursor = 0;
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if (line.Count >= 2 && line[0].kind == TokenKind.Identifier && line[1].kind == TokenKind.Colon)
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{
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statements.Add(new LabelStatement(line[0].text, line[0].position));
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cursor = 2;
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}
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if (cursor >= line.Count)
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{
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return;
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}
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Token head = line[cursor];
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if (head.kind != TokenKind.Identifier)
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{
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throw new AsmException("expected an instruction or directive but found '" + head.text + "'", head.position);
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}
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if (cursor + 1 < line.Count && line[cursor + 1].isIdentifier("EQU"))
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{
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List<Token> expression = line.GetRange(cursor + 2, line.Count - cursor - 2);
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if (expression.Count == 0)
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{
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throw new AsmException("EQU needs a value", head.position);
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}
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statements.Add(new ConstantStatement(head.text, expression, head.position));
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return;
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}
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if (directives.Contains(head.text))
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{
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statements.Add(parseDirective(head, line, cursor + 1));
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return;
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}
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var operands = parseOperands(line, cursor + 1);
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statements.Add(new InstructionStatement(head.text, operands, head.position));
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}
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Statement parseDirective(Token head, List<Token> line, int start)
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{
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List<Token> body = line.GetRange(start, line.Count - start);
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if (head.isIdentifier("ORG"))
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{
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requireExpression(body, head.position, "ORG");
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return new OrgStatement(body, head.position);
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}
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if (head.isIdentifier("ALIGN"))
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{
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requireExpression(body, head.position, "ALIGN");
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return new AlignStatement(body, head.position);
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}
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bool word = head.isIdentifier("DW");
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List<IReadOnlyList<Token>> items = splitByComma(body, head.position);
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if (items.Count == 0)
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{
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throw new AsmException(head.text + " needs at least one value", head.position);
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}
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return new DataStatement(word, items, head.position);
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}
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List<Operand> parseOperands(List<Token> line, int start)
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{
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var operands = new List<Operand>();
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if (start >= line.Count)
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{
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return operands;
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}
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List<Token> body = line.GetRange(start, line.Count - start);
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foreach (IReadOnlyList<Token> group in splitByComma(body, line[start].position))
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{
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operands.Add(classifyOperand(group));
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}
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return operands;
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}
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static Operand classifyOperand(IReadOnlyList<Token> group)
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{
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if (group.Count == 0)
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{
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throw new AsmException("empty operand", new SourcePosition(0, 0));
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}
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SourcePosition position = group[0].position;
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if (group.Count == 3 && group[0].kind == TokenKind.LeftBracket
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&& group[1].isIdentifier("I") && group[2].kind == TokenKind.RightBracket)
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{
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return Operand.special(OperandKind.IndexIndirect, position);
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}
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if (group.Count == 1 && group[0].kind == TokenKind.Identifier)
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{
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int register = registerIndex(group[0].text);
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if (register >= 0)
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{
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return Operand.register(register, position);
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}
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OperandKind? special = specialRegister(group[0].text);
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if (special.HasValue)
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{
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return Operand.special(special.Value, position);
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}
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}
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if (group.Count == 3 && group[1].kind == TokenKind.Minus
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&& group[0].kind == TokenKind.Identifier && group[2].kind == TokenKind.Identifier)
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{
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int start = registerIndex(group[0].text);
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int end = registerIndex(group[2].text);
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if (start >= 0 && end >= 0)
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{
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return Operand.registerRange(start, end, position);
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}
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}
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return Operand.immediate(new List<Token>(group), position);
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}
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static OperandKind? specialRegister(string text) => text.ToUpperInvariant() switch
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{
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"I" => OperandKind.IndexRegister,
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"DT" => OperandKind.DelayTimer,
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"ST" => OperandKind.SoundTimer,
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"K" => OperandKind.KeyReg,
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"F" => OperandKind.FontReg,
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"HF" => OperandKind.BigFontReg,
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"B" => OperandKind.BcdReg,
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"R" => OperandKind.RplReg,
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_ => null,
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};
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static int registerIndex(string text)
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{
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if (text.Length != 2 || (text[0] != 'V' && text[0] != 'v'))
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{
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return -1;
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}
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char digit = text[1];
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if (digit >= '0' && digit <= '9')
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{
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return digit - '0';
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}
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if (digit >= 'A' && digit <= 'F')
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{
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return digit - 'A' + 10;
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}
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if (digit >= 'a' && digit <= 'f')
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{
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return digit - 'a' + 10;
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}
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return -1;
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}
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static List<IReadOnlyList<Token>> splitByComma(List<Token> body, SourcePosition position)
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{
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var groups = new List<IReadOnlyList<Token>>();
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var current = new List<Token>();
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int depth = 0;
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foreach (Token token in body)
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{
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if (token.kind == TokenKind.LeftParen || token.kind == TokenKind.LeftBracket)
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{
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depth++;
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}
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else if (token.kind == TokenKind.RightParen || token.kind == TokenKind.RightBracket)
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{
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depth--;
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}
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if (token.kind == TokenKind.Comma && depth == 0)
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{
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if (current.Count == 0)
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{
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throw new AsmException("empty operand before comma", token.position);
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}
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groups.Add(current);
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current = new List<Token>();
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continue;
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}
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current.Add(token);
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}
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if (current.Count > 0)
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{
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groups.Add(current);
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}
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return groups;
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}
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static void requireExpression(List<Token> body, SourcePosition position, string directive)
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{
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if (body.Count == 0)
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{
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throw new AsmException(directive + " needs an expression", position);
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}
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}
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List<Token> takeLine()
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{
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var line = new List<Token>();
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while (current().kind != TokenKind.EndOfLine && current().kind != TokenKind.EndOfFile)
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{
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line.Add(current());
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index++;
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}
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if (current().kind == TokenKind.EndOfLine)
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{
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index++;
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}
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return line;
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}
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Token current() => tokens[index];
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}
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